Datasets:

Rishabh56
/

chemistry-class10-dataset

instruction stringclasses 1 value	input stringlengths 76 3.3k	output stringlengths 79 395
Summarize the following historical passage:	Science 156 Magnification The magnification produced by a lens, similar to that for spherical mirrors, is defined as the ratio of the height of the image and the height of the object. Magnification is represented by the letter m. If h is the height of the object and h′ is the height of the image given by a lens, then the magnification produced by the lens is given by, m = Height of the Image Height of the object = h h ′ (9.9) Magnification produced by a lens is also related to the object-distance u, and the image-distance v. This relationship is given by Magnification (m ) = h′/h = v/u (9.10) Example 9.3 A concave lens has focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also, find the magnification produced by the lens. Solution A concave lens always forms a virtual, erect image on the same side of the object. Image-distance v = –10 cm; Focal length f = –15 cm; Object-distance u = ? Since 1 1 1 v u f − = or, 1 1 1 – u v f = ( ) 1 1 1 1 1 – – –10 –15 10 15 u = = + 1 3 2 1 30 30 u − + = = − or, u = – 30 cm Thus, the object-distance is 30 cm. Magnification m = v/u m = − − = + 10cm 30cm 1 3 0.33 ; The positive sign shows that the image is erect and virtual. The image is one-third of the size of the object. Example 9.4 A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image. Also find its magnification. 2024-25	Science 156 Magnification The magnification produced by a lens, similar to that for spherical mirrors, is defined as the ratio of the height of the image and the height of the object. Magnification is represented by the letter m. If h is the height of the object and h′ is...
Summarize the following historical passage:	Science 182 Figure 11.7 Figure 11.7 Figure 11.7 Figure 11.7 Figure 11.7 Resistors in parallel You will observe that the value of the current in the ammeter is the same, independent of its position in the electric circuit. It means that in a series combination of resistors the current is the same in every part of the circuit or the same current through each resistor. Activity 11.4 Activity 11.4 Activity 11.4 Activity 11.4 Activity 11.4 n Join three resistors of different values in series. Connect them with a battery, an ammeter and a plug key, as shown in Fig. 11.6. You may use the resistors of values like 1 Ω, 2 Ω, 3 Ω etc., and a battery of 6 V for performing this Activity. n Plug the key. Note the ammeter reading. n Change the position of ammeter to anywhere in between the resistors. Note the ammeter reading each time. n Do you find any change in the value of current through the ammeter? 11.6.1 Resistors in Series What happens to the value of current when a number of resistors are connected in series in a circuit? What would be their equivalent resistance? Let us try to understand these with the help of the following activities. Figure 11.7 shows a combination of resistors in which three resistors are connected together between points X and Y. Here, the resistors are said to be connected in parallel. 2024-25	Science 182 Figure 11.7 Figure 11.7 Figure 11.7 Figure 11.7 Figure 11.7 Resistors in parallel You will observe that the value of the current in the ammeter is the same, independent of its position in the electric circuit. It means that in a series combination of resistors the current is...
Summarize the following historical passage:	Our Environment 215 Activity 13.7 Activity 13.7 Activity 13.7 Activity 13.7 Activity 13.7 n Find out what happens to the waste generated at home. Is there a system in place to collect this waste? n Find out how the local body (panchayat, municipal corporation, resident welfare association) deals with the waste. Are there mechanisms in place to treat the biodegradable and non- biodegradable wastes separately? n Calculate how much waste is generated at home in a day. n How much of this waste is biodegradable? n Calculate how much waste is generated in the classroom in a day. n How much of this waste is biodegradable? n Suggest ways of dealing with this waste. Improvements in our life-style have resulted in greater amounts of waste material generation. Changes in attitude also have a role to play, with more and more things we use becoming disposable. Changes in packaging have resulted in much of our waste becoming non- biodegradable. What do you think will be the impact of these on our environment? Activity 13.8 Activity 13.8 Activity 13.8 Activity 13.8 Activity 13.8 n Find out how the sewage in your locality is treated. Are there mechanisms in place to ensure that local water bodies are not polluted by untreated sewage. n Find out how the local industries in your locality treat their wastes. Are there mechanisms in place to ensure that the soil and water are not polluted by this waste? Disposable cups in trains If you ask your parents, they will probably remember a time when tea in trains was served in plastic glasses which had to be returned to the vendor. The introduction of disposable cups was hailed as a step forward for reasons of hygiene. No one at that time perhaps thought about the impact caused by the disposal of millions of these cups on a daily basis. Some time back, kulhads, that is, disposable cups made of clay, were suggested as an alternative. But a little thought showed that making these kulhads on a large scale would result in the loss of the fertile top-soil. Now disposable paper-cups are being used. What do you think are the advantages of disposable paper-cups over disposable plastic cups? Think it over 2024-25	Our Environment 215 Activity 13.7 Activity 13.7 Activity 13.7 Activity 13.7 Activity 13.7 n Find out what happens to the waste generated at home. Is there a system in place to collect this waste? n Find out how the local body (panchayat, municipal corporation, resident welfare association) deals with the...
Summarize the following historical passage:	Science 114 ? because the copy pushed out would not have any organised cellular structure for maintaining life processes. Therefore, DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells. These two cells are of course similar, but are they likely to be absolutely identical? The answer to this question will depend on how accurately the copying reactions involved occur. No bio-chemical reaction is absolutely reliable. Therefore, it is only to be expected that the process of copying the DNA will have some variations each time. As a result, the DNA copies generated will be similar, but may not be identical to the original. Some of these variations might be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell will simply die. On the other hand, there could still be many other variations in the DNA copies that would not lead to such a drastic outcome. Thus, the surviving cells are similar to, but subtly different from each other. This inbuilt tendency for variation during reproduction is the basis for evolution, as we will discuss in the next chapter. 7.1.1 The Importance of Variation Populations of organisms fill well-defined places, or niches, in the ecosystem, using their ability to reproduce. The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Reproduction is therefore linked to the stability of populations of species. However, niches can change because of reasons beyond the control of the organisms. Temperatures on earth can go up or down, water levels can vary, or there could be meteorite hits, to think of a few examples. If a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Thus, if there were a population of bacteria living in temperate waters, and if the water temperature were to be increased by global warming, most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time. Q U E S T I O N S 1. What is the importance of DNA copying in reproduction? 2. Why is variation beneficial to the species but not necessarily for the individual? 2024-25	Science 114 ? because the copy pushed out would not have any organised cellular structure for maintaining life processes. Therefore, DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give...
Summarize the following historical passage:	Magnetic Effects of Electric Current 205 Figure 12.15 Figure 12.15 Figure 12.15 Figure 12.15 Figure 12.15 A schematic diagram of one of the common domestic circuits Q U E S T I O N S ? Figure 12.15 gives a schematic diagram of one of the common domestic circuits. In each separate circuit, different appliances can be connected across the live and neutral wires. Each appliance has a separate switch to ‘ON’/‘OFF’ the flow of current through it. In order that each appliance has equal potential difference, they are connected parallel to each other. Electric fuse is an important component of all domestic circuits. We have already studied the principle and working of a fuse in the previous chapter (see Section 11.7). A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Overloading can occur when the live wire and the neutral wire come into direct contact. (This occurs when the insulation of wires is damaged or there is a fault in the appliance.) In such a situation, the current in the circuit abruptly increases. This is called short-circuiting. The use of an electric fuse prevents the electric circuit and the appliance from a possible damage by stopping the flow of unduly high electric current. The Joule heating that takes place in the fuse melts it to break the electric circuit. Overloading can also occur due to an accidental hike in the supply voltage. Sometimes overloading is caused by connecting too many appliances to a single socket. 1. Name two safety measures commonly used in electric circuits and appliances. 2. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain. 3. What precaution should be taken to avoid the overloading of domestic electric circuits? 2024-25	Magnetic Effects of Electric Current 205 Figure 12.15 Figure 12.15 Figure 12.15 Figure 12.15 Figure 12.15 A schematic diagram of one of the common domestic circuits Q U E S T I O N S ? Figure 12.15 gives a schematic diagram of one of the common domestic circuits. In...
Summarize the following historical passage:	Science 186 n Take out the plug from the key. Remove the ammeter and voltmeter from the circuit. Insert the ammeter in series with the resistor R1, as shown in Fig. 11.11. Note the ammeter reading, I1. Figure 11.11 Figure 11.11 Figure 11.11 Figure 11.11 Figure 11.11 n Similarly, measure the currents through R2 and R3. Let these be I2 and I3, respectively. What is the relationship between I, I1, I2 and I3? It is observed that the total current I, is equal to the sum of the separate currents through each branch of the combination. I = I1 + I2 + I3 (11.15) Let Rp be the equivalent resistance of the parallel combination of resistors. By applying Ohm’s law to the parallel combination of resistors, we have I = V/Rp (11.16) On applying Ohm’s law to each resistor, we have I1 = V /R1; I2 = V /R2; and I3 = V /R3 (11.17) From Eqs. (11.15) to (11.17), we have V/Rp = V/R1 + V/R2 + V/R3 or 1/Rp = 1/R1 + 1/R2 + 1/R3 (11.18) Thus, we may conclude that the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances. Example 11.8 In the circuit diagram given in Fig. 11.10, suppose the resistors R1, R2 and R3 have the values 5 Ω, 10 Ω, 30 Ω, respectively, which have been connected to a battery of 12 V. Calculate (a) the current through each resistor, (b) the total current in the circuit, and (c) the total circuit resistance. Solution R1 = 5 Ω, R2 = 10 Ω, and R3 = 30 Ω. Potential difference across the battery, V = 12 V. This is also the potential difference across each of the individual resistor; therefore, to calculate the current in the resistors, we use Ohm’s law. The current I1, through R1 = V/ R1 I1 = 12 V/5 Ω = 2.4 A. 2024-25	Science 186 n Take out the plug from the key. Remove the ammeter and voltmeter from the circuit. Insert the ammeter in series with the resistor R1, as shown in Fig. 11.11. Note the ammeter reading, I1. Figure 11.11 Figure 11.11 Figure 11.11 Figure 11.11 Figure 11.11 n Similarly, measure...
Summarize the following historical passage:	Science 94 pumping system. To avoid this, the blood has platelet cells which circulate around the body and plug these leaks by helping to clot the blood at these points of injury. Lymph There is another type of fluid also involved in transportation. This is called lymph or tissue fluid. Through the pores present in the walls of capillaries some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form the tissue fluid or lymph. It is similar to the plasma of blood but colourless and contains less protein. Lymph drains into lymphatic capillaries from the intercellular spaces, which join to form large lymph vessels that finally open into larger veins. Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood. 5.4.2 Transportation in Plants We have discussed earlier how plants take in simple compounds such as CO2 and photosynthesise energy stored in their chlorophyll-containing organs, namely leaves. The other kinds of raw materials needed for building plant bodies will also have to be taken up separately. For plants, the soil is the nearest and richest source of raw materials like nitrogen, phosphorus and other minerals. The absorption of these substances therefore occurs through the part in contact with the soil, namely roots. If the distances between soil-contacting organs and chlorophyll- containing organs are small, energy and raw materials can easily diffuse to all parts of the plant body. But if these distances become large because of changes in plant body design, diffusion processes will not be sufficient to provide raw material in leaves and energy in roots. A proper system of transportation is therefore essential in such situations. Energy needs differ between different body designs. Plants do not move, and plant bodies have a large proportion of dead cells in many tissues. As a result, plants have low energy needs, and can use relatively slow transport systems. The distances over which transport systems have to operate, however, can be very large in plants such as very tall trees. Plant transport systems will move energy stores from leaves and raw materials from roots. These two pathways are constructed as independently organised conducting tubes. One, the xylem moves water and minerals obtained from the soil. The other, phloem transports products of photosynthesis from the leaves where they are synthesised to other parts of the plant. We have studied the structure of these tissues in detail in Class IX. Transport of water In xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plant. At the roots, cells in contact with the soil actively take up ions. This creates a difference in the concentration of these ions between the root and the soil. Water, therefore, 2024-25	Science 94 pumping system. To avoid this, the blood has platelet cells which circulate around the body and plug these leaks by helping to clot the blood at these points of injury. Lymph There is another type of fluid also involved in transportation. This is called lymph or tissue fluid....
Summarize the following historical passage:	The Human Eye and the Colourful World 165 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM You have learnt how light gets refracted through a rectangular glass slab. For parallel refracting surfaces, as in a glass slab, the emergent ray is parallel to the incident ray. However, it is slightly displaced laterally. How would light get refracted through a transparent prism? Consider a triangular glass prism. It has two triangular bases and three rectangular lateral surfaces. These surfaces are inclined to each other. The angle between its two lateral faces is called the angle of the prism. Let us now do an activity to study the refraction of light through a triangular glass prism. n Eyes must be removed within 4-6 hours after death. Inform the nearest eye bank immediately. n The eye bank team will remove the eyes at the home of the deceased or at a hospital. n Eye removal takes only 10-15 minutes. It is a simple process and does not lead to any disfigurement. n Persons who were infected with or died because of AIDS, Hepatitis B or C, rabies, acute leukaemia, tetanus, cholera, meningitis or encephalitis cannot donate eyes. An eye bank collects, evaluates and distributes the donated eyes. All eyes donated are evaluated using strict medical standards. Those donated eyes found unsuitable for transplantation are used for valuable research and medical education. The identities of both the donor and the recipient remain confidential. One pair of eyes gives vision to up to FOUR CORNEAL BLIND PEOPLE. Activity 10.1 Activity 10.1 Activity 10.1 Activity 10.1 Activity 10.1 n Fix a sheet of white paper on a drawing board using drawing pins. n Place a glass prism on it in such a way that it rests on its triangular base. Trace the outline of the prism using a pencil. n Draw a straight line PE inclined to one of the refracting surfaces, say AB, of the prism. n Fix two pins, say at points P and Q, on the line PE as shown in Fig. 10.4. n Look for the images of the pins, fixed at P and Q, through the other face AC. n Fix two more pins, at points R and S, such that the pins at R and S and the images of the pins at P and Q lie on the same straight line. n Remove the pins and the glass prism. n The line PE meets the boundary of the prism at point E (see Fig. 10.4). Similarly, join and produce the points R and S. Let these lines meet the boundary of the prism at E and F, respectively. Join E and F. n Draw perpendiculars to the refracting surfaces AB and AC of the prism at points E and F, respectively. n Mark the angle of incidence (∠i), the angle of refraction (∠r) and the angle of emergence (∠e) as shown in Fig. 10.4. 2024-25	The Human Eye and the Colourful World 165 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM 10.3 REFRACTION OF LIGHT THROUGH A PRISM You have learnt how light gets refracted...
Summarize the following historical passage:	Control and Coordination 103 Can you now trace the sequence of events which occur when a bright light is focussed on your eyes? 6.1.2 Human Brain Is reflex action the only function of the spinal cord? Obviously not, since we know that we are thinking beings. Spinal cord is made up of nerves which supply information to think about. Thinking involves more complex mechanisms and neural connections. These are concentrated in the brain, which is the main coordinating centre of the body. The brain and spinal cord constitute the central nervous system (Fig. 6.3). They receive information from all parts of the body and integrate it. We also think about our actions. Writing, talking, moving a chair, clapping at the end of a programme are examples of voluntary actions which are based on deciding what to do next. So, the brain also has to send messages to muscles. This is the second way in which the nervous system communicates with the muscles. The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord. The brain thus allows us to think and take actions based on that thinking. As you will expect, this is accomplished through a complex design, with different parts of the brain responsible for integrating different inputs and outputs. The brain has three such major parts or regions, namely the fore-brain, mid-brain and hind-brain. The fore-brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing, smell, sight and so on. There are separate areas of association where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in the brain. Based on Figure 6.2 Figure 6.2 Figure 6.2 Figure 6.2 Figure 6.2 Reflex arc 2024-25	Control and Coordination 103 Can you now trace the sequence of events which occur when a bright light is focussed on your eyes? 6.1.2 Human Brain Is reflex action the only function of the spinal cord? Obviously not, since we know that we are thinking beings. Spinal cord is made...
Summarize the following historical passage:	How do Organisms Reproduce? 115 Figure 7.1(a) Figure 7.1(a) Figure 7.1(a) Figure 7.1(a) Figure 7.1(a) Binary fission in Amoeba Activity 7.2 Activity 7.2 Activity 7.2 Activity 7.2 Activity 7.2 7.2 MODES OF REPRODUCTION USED BY SINGLE 7.2 MODES OF REPRODUCTION USED BY SINGLE 7.2 MODES OF REPRODUCTION USED BY SINGLE 7.2 MODES OF REPRODUCTION USED BY SINGLE 7.2 MODES OF REPRODUCTION USED BY SINGLE ORGANISMS ORGANISMS ORGANISMS ORGANISMS ORGANISMS Activity 7.1 Activity 7.1 Activity 7.1 Activity 7.1 Activity 7.1 n Dissolve about 10 gm of sugar in 100 mL of water. n Take 20 mL of this solution in a test tube and add a pinch of yeast granules to it. n Put a cotton plug on the mouth of the test tube and keep it in a warm place. n After 1 or 2 hours, put a small drop of yeast culture from the test tube on a slide and cover it with a coverslip. n Observe the slide under a microscope. n Wet a slice of bread, and keep it in a cool, moist and dark place. n Observe the surface of the slice with a magnifying glass. n Record your observations for a week. Compare and contrast the ways in which yeast grows in the first case, and how mould grows in the second. Having discussed the context in which reproductive processes work, let us now examine how different organisms actually reproduce. The modes by which various organisms reproduce depend on the body design of the organisms. 7.2.1 Fission For unicellular organisms, cell division, or fission, leads to the creation of new individuals. Many different patterns of fission have been observed. Many bacteria and protozoa simply split into two equal halves during cell division. In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane. Activity 7.3 Activity 7.3 Activity 7.3 Activity 7.3 Activity 7.3 n Observe a permanent slide of Amoeba under a microscope. n Similarly observe another permanent slide of Amoeba showing binary fission. n Now, compare the observations of both the slides. However, some unicellular organisms show somewhat more organisation of their bodies, such as is seen in Leishmania (which cause kala-azar), which have a whip-like structure at one end of the cell. In such organisms, binary fission occurs in a definite orientation in relation to Figure 7.1(b) Figure 7.1(b) Figure 7.1(b) Figure 7.1(b) Figure 7.1(b) Binary fission in Leishmania (a) (b) (c) (d) (e) (f) 2024-25	How do Organisms Reproduce? 115 Figure 7.1(a) Figure 7.1(a) Figure 7.1(a) Figure 7.1(a) Figure 7.1(a) Binary fission in Amoeba Activity 7.2 Activity 7.2 Activity 7.2 Activity 7.2 Activity 7.2 7.2 MODES OF REPRODUCTION USED BY SINGLE 7.2 MODES OF REPRODUCTION USED BY SINGLE 7.2 MODES OF REPRODUCTION USED BY SINGLE...
Summarize the following historical passage:	Our Environment 217 (c) Goat, cow and elephant (d) Grass, fish and goat 3. Which of the following are environment-friendly practices? (a) Carrying cloth-bags to put purchases in while shopping (b) Switching off unnecessary lights and fans (c) Walking to school instead of getting your mother to drop you on her scooter (d) All of the above 4. What will happen if we kill all the organisms in one trophic level? 5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem? 6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem? 7. What are the problems caused by the non-biodegradable wastes that we generate? 8. If all the waste we generate is biodegradable, will this have no impact on the environment? 9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? 2024-25	Our Environment 217 (c) Goat, cow and elephant (d) Grass, fish and goat 3. Which of the following are environment-friendly practices? (a) Carrying cloth-bags to put purchases in while shopping (b) Switching off unnecessary lights and fans (c) Walking to school instead of getting your mother to drop you on...
Summarize the following historical passage:	Science 60 Figure 4.4 Figure 4.4 Figure 4.4 Figure 4.4 Figure 4.4 Triple bond between two nitrogen atoms Figure 4.3 Figure 4.3 Figure 4.3 Figure 4.3 Figure 4.3 Double bond between two oxygen atoms electronic configuration of the nearest noble gas, helium, which has two electrons in its K shell. We can depict this using dots or crosses to represent valence electrons (Fig. 4.1). The shared pair of electrons is said to constitute a single covalent bond between the two hydrogen atoms. A single covalent bond is also represented by a line between the two atoms, as shown in Fig. 4.2. The atomic number of chlorine is 17. What would be its electronic configuration and its valency? Chlorine forms a diatomic molecule, Cl2. Can you draw the electron dot structure for this molecule? Note that only the valence shell electrons need to be depicted. In the case of oxygen, we see the formation of a double bond between two oxygen atoms. This is because an atom of oxygen has six electrons in its L shell (the atomic number of oxygen is eight) and it requires two more electrons to complete its octet. So each atom of oxygen shares two electrons with another atom of oxygen to give us the structure shown in Fig. 4.3. The two electrons contributed by each oxygen atom give rise to two shared pairs of electrons. This is said to constitute a double bond between the two atoms. Can you now depict a molecule of water showing the nature of bonding between one oxygen atom and two hydrogen atoms? Does the molecule have single bonds or double bonds? What would happen in the case of a diatomic molecule of nitrogen? Nitrogen has the atomic number 7. What would be its electronic configuration and its combining capacity? In order to attain an octet, each nitrogen atom in a molecule of nitrogen contributes three electrons giving rise to three shared pairs of electrons. This is said to constitute a triple bond between the two atoms. The electron dot structure of N2 and its triple bond can be depicted as in Fig. 4.4. A molecule of ammonia has the formula NH3. Can you draw the electron dot structure for this molecule showing how all four atoms achieve noble gas configuration? Will the molecule have single, double or triple bonds? Let us now take a look at methane, which is a compound of carbon. Methane is widely used as a fuel and is a major component of bio-gas and Compressed Natural Gas (CNG). It is also one of the simplest compounds formed by carbon. Methane has a formula CH4. Hydrogen, as you know, has a valency of 1. Carbon is tetravalent because it has four valence electrons. In order to achieve noble gas configuration, carbon shares these electrons with four atoms of hydrogen as shown in Fig. 4.5. Such bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds. Covalently bonded molecules are seen to have strong bonds within the molecule, but inter- molecular forces are weak. This gives rise to the low melting and boiling Figure 4.1 Figure 4.1 Figure 4.1 Figure 4.1 Figure 4.1 A molecule of hydrogen Figure 4.2 Figure 4.2 Figure 4.2 Figure 4.2 Figure 4.2 Single bond between two hydrogen atoms 2024-25	Science 60 Figure 4.4 Figure 4.4 Figure 4.4 Figure 4.4 Figure 4.4 Triple bond between two nitrogen atoms Figure 4.3 Figure 4.3 Figure 4.3 Figure 4.3 Figure 4.3 Double bond between two oxygen atoms electronic configuration of the nearest noble gas, helium, which has two electrons in its K shell....
Summarize the following historical passage:	Science 80 class, even if we are just asleep, this maintenance job has to go on. The processes which together perform this maintenance job are life processes. Since these maintenance processes are needed to prevent damage and break-down, energy is needed for them. This energy comes from outside the body of the individual organism. So there must be a process to transfer a source of energy from outside the body of the organism, which we call food, to the inside, a process we commonly call nutrition. If the body size of the organisms is to grow, additional raw material will also be needed from outside. Since life on earth depends on carbon- based molecules, most of these food sources are also carbon-based. Depending on the complexity of these carbon sources, different organisms can then use different kinds of nutritional processes. The outside sources of energy could be quite varied, since the environment is not under the control of the individual organism. These sources of energy, therefore, need to be broken down or built up in the body, and must be finally converted to a uniform source of energy that can be used for the various molecular movements needed for maintaining living structures, as well as to the kind of molecules the body needs to grow. For this, a series of chemical reactions in the body are necessary. Oxidising-reducing reactions are some of the most common chemical means to break-down molecules. For this, many organisms use oxygen sourced from outside the body. The process of acquiring oxygen from outside the body, and to use it in the process of break-down of food sources for cellular needs, is what we call respiration. In the case of a single-celled organism, no specific organs for taking in food, exchange of gases or removal of wastes may be needed because the entire surface of the organism is in contact with the environment. But what happens when the body size of the organism increases and the body design becomes more complex? In multi-cellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus, simple diffusion will not meet the requirements of all the cells. We have seen previously how, in multi-cellular organisms, various body parts have specialised in the functions they perform. We are familiar with the idea of these specialised tissues, and with their organisation in the body of the organism. It is therefore not surprising that the uptake of food and of oxygen will also be the function of specialised tissues. However, this poses a problem, since the food and oxygen are now taken up at one place in the body of the organisms, while all parts of the body need them. This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body. When chemical reactions use the carbon source and the oxygen for energy generation, they create by-products that are not only useless for the cells of the body, but could even be harmful. These waste by- products are therefore needed to be removed from the body and discarded outside by a process called excretion. Again, if the basic rules for body 2024-25	Science 80 class, even if we are just asleep, this maintenance job has to go on. The processes which together perform this maintenance job are life processes. Since these maintenance processes are needed to prevent damage and break-down, energy is needed for them. This energy comes from outside the body...
Summarize the following historical passage:	Science 148 The following are the laws of refraction of light. (i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. (ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction. (This is true for angle 0 < i < 90o) If i is the angle of incidence and r is the angle of refraction, then, sin sin i r = constant (9.4) This constant value is called the refractive index of the second medium with respect to the first. Let us study about refractive index in some detail. 9.3.2 The Refractive Index You have already studied that a ray of light that travels obliquely from one transparent medium into another will change its direction in the second medium. The extent of the change in direction that takes place in a given pair of media may be expressed in terms of the refractive index, the “constant” appearing on the right-hand side of Eq.(9.4). The refractive index can be linked to an important physical quantity, the relative speed of propagation of light in different media. It turns out that light propagates with different speeds in different media. Light travels fastest in vacuum with speed of 3×108 m s–1. In air, the speed of light is only marginally less, compared to that in vacuum. It reduces considerably in glass or water. The value of the refractive index for a given pair of media depends upon the speed of light in the two media, as given below. Consider a ray of light travelling from medium 1 into medium 2, as shown in Fig.9.11. Let v1 be the speed of light in medium 1 and v2 be the speed of light in medium 2. The refractive index of medium 2 with respect to medium 1 is given by the ratio of the speed of light in medium 1 and the speed of light in medium 2. This is usually represented by the symbol n21. This can be expressed in an equation form as n21= Speed of light in medium 1 Speed of light in medium 2 = v v 1 2 (9.5) By the same argument, the refractive index of medium 1 with respect to medium 2 is represented as n12. It is given by n12= Speed of light in medium 2 Speed of light in medium 1 = v v 2 1 (9.6) If medium 1 is vacuum or air, then the refractive index of medium 2 is considered with respect to vacuum. This is called the absolute refractive index of the medium. It is simply represented as n2. If c is the speed of Figure 9.11 Figure 9.11 Figure 9.11 Figure 9.11 Figure 9.11 2024-25	Science 148 The following are the laws of refraction of light. (i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. (ii) The ratio of sine of angle of incidence to the...
Summarize the following historical passage:	Science 78 4. Explain the nature of the covalent bond using the bond formation in CH3Cl. 5. Draw the electron dot structures for (a) ethanoic acid. (b) H2S. (c) propanone. (d) F2 . 6. What is an homologous series? Explain with an example. 7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties? 8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? 9. Why are carbon and its compounds used as fuels for most applications? 10. Explain the formation of scum when hard water is treated with soap. 11. What change will you observe if you test soap with litmus paper (red and blue)? 12. What is hydrogenation? What is its industrial application? 13. Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4. 14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons. 15. Explain the mechanism of the cleaning action of soaps. I Use molecular model kits to make models of the compounds you have learnt in this Chapter. II n Take about 20 mL of castor oil/cotton seed oil/linseed oil/soyabean oil in a beaker. Add 30 mL of 20 % sodium hydroxide solution. Heat the mixture with continuous stirring for a few minutes till the mixture thickens. Add 5-10 g of common salt to this. Stir the mixture well and allow it to cool. n You can cut out the soap in fancy shapes. You can also add perfume to the soap before it sets. Group Activity 2024-25	Science 78 4. Explain the nature of the covalent bond using the bond formation in CH3Cl. 5. Draw the electron dot structures for (a) ethanoic acid. (b) H2S. (c) propanone. (d) F2 . 6. What is an homologous series? Explain with an example. 7. How can ethanol and ethanoic acid...
Summarize the following historical passage:	Metals and Non-metals 55 In which cases will you find displacement reactions taking place? 2. Which metals do not corrode easily? 3. What are alloys? Q U E S T I O N S ? 1. Metallic oxides of zinc, magnesium and copper were heated with the following metals. Metal Zinc Magnesium Copper Zinc oxide Magnesium oxide Copper oxide What you have learnt n Elements can be classified as metals and non-metals. n Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid. n Metals can form positive ions by losing electrons to non-metals. n Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known as amphoteric oxides. n Different metals have different reactivities with water and dilute acids. n A list of common metals arranged in order of their decreasing reactivity is known as an activity series. n Metals above hydrogen in the Activity series can displace hydrogen from dilute acids. n A more reactive metal displaces a less reactive metal from its salt solution. n Metals occur in nature as free elements or in the form of their compounds. n The extraction of metals from their ores and then refining them for use is known as metallurgy. n An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. n The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion. n Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity. 2024-25	Metals and Non-metals 55 In which cases will you find displacement reactions taking place? 2. Which metals do not corrode easily? 3. What are alloys? Q U E S T I O N S ? 1. Metallic oxides of zinc, magnesium and copper were heated with the following metals. Metal...
Summarize the following historical passage:	Science 206 What you have learnt n A compass needle is a small magnet. Its one end, which points towards north, is called a north pole, and the other end, which points towards south, is called a south pole. n A magnetic field exists in the region surrounding a magnet, in which the force of the magnet can be detected. n Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take. Field lines are shown closer together where the magnetic field is greater. n A metallic wire carrying an electric current has associated with it a magnetic field. The field lines about the wire consist of a series of concentric circles whose direction is given by the right-hand rule. n The pattern of the magnetic field around a conductor due to an electric current flowing through it depends on the shape of the conductor. The magnetic field of a solenoid carrying a current is similar to that of a bar magnet. n An electromagnet consists of a core of soft iron wrapped around with a coil of insulated copper wire. n A current-carrying conductor when placed in a magnetic field experiences a force. If the direction of the field and that of the current are mutually perpendicular to each other, then the force acting on the conductor will be perpendicular to both and will be given by Fleming’s left-hand rule. n In our houses we receive AC electric power of 220 V with a frequency of 50 Hz. One of the wires in this supply is with red insulation, called live wire. The other one is of black insulation, which is a neutral wire. The potential difference between the two is 220 V. The third is the earth wire that has green insulation and this is connected to a metallic body deep inside earth. It is used as a safety measure to ensure that any leakage of current to a metallic body does not give any severe shock to a user. n Fuse is the most important safety device, used for protecting the circuits due to short-circuiting or overloading of the circuits. 2024-25	Science 206 What you have learnt n A compass needle is a small magnet. Its one end, which points towards north, is called a north pole, and the other end, which points towards south, is called a south pole. n A magnetic field exists in the region surrounding a magnet,...
Summarize the following historical passage:	Electricity 183 Activity 11.5 Activity 11.5 Activity 11.5 Activity 11.5 Activity 11.5 n In Activity 11.4, insert a voltmeter across the ends X and Y of the series combination of three resistors, as shown in Fig. 11.6. n Plug the key in the circuit and note the voltmeter reading. It gives the potential difference across the series combination of resistors. Let it be V. Now measure the potential difference across the two terminals of the battery. Compare the two values. n Take out the plug key and disconnect the voltmeter. Now insert the voltmeter across the ends X and P of the first resistor, as shown in Fig. 11.8. Figure 11.8 Figure 11.8 Figure 11.8 Figure 11.8 Figure 11.8 n Plug the key and measure the potential difference across the first resistor. Let it be V1. n Similarly, measure the potential difference across the other two resistors, separately. Let these values be V2 and V3, respectively. n Deduce a relationship between V, V1, V2 and V3. You will observe that the potential difference V is equal to the sum of potential differences V1, V2, and V3. That is the total potential difference across a combination of resistors in series is equal to the sum of potential difference across the individual resistors. That is, V = V1 + V2 + V3 (11.11) In the electric circuit shown in Fig. 11.8, let I be the current through the circuit. The current through each resistor is also I. It is possible to replace the three resistors joined in series by an equivalent single resistor of resistance R, such that the potential difference V across it, and the current I through the circuit remains the same. Applying the Ohm’s law to the entire circuit, we have V = I R (11.12) 2024-25	Electricity 183 Activity 11.5 Activity 11.5 Activity 11.5 Activity 11.5 Activity 11.5 n In Activity 11.4, insert a voltmeter across the ends X and Y of the series combination of three resistors, as shown in Fig. 11.6. n Plug the key in the circuit and note the voltmeter reading. It...
Summarize the following historical passage:	The Human Eye and the Colourful World 10 CHAPTER Y ou have studied in the previous chapter about refraction of light by lenses. You also studied the nature, position and relative size of images formed by lenses. How can these ideas help us in the study of the human eye? The human eye uses light and enables us to see objects around us. It has a lens in its structure. What is the function of the lens in a human eye? How do the lenses used in spectacles correct defects of vision? Let us consider these questions in this chapter. We have learnt in the previous chapter about light and some of its properties. In this chapter, we shall use these ideas to study some of the optical phenomena in nature. We shall also discuss about rainbow formation, splitting of white light and blue colour of the sky. 10.1 THE HUMAN EYE The human eye is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us. On closing the eyes, we can identify objects to some extent by their smell, taste, sound they make or by touch. It is, however, impossible to identify colours while closing the eyes. Thus, of all the sense organs, the human eye is the most significant one as it enables us to see the beautiful, colourful world around us. The human eye is like a camera. Its lens system forms an image on a light-sensitive screen called the retina. Light enters the eye through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball as shown in Fig. 10.1. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm. Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea. The crystalline lens merely provides the finer adjustment of focal length required to focus objects at different distances on the retina. We find a structure called iris behind the cornea. Iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light Figure 10.1 Figure 10.1 Figure 10.1 Figure 10.1 Figure 10.1 The human eye 2024-25	The Human Eye and the Colourful World 10 CHAPTER Y ou have studied in the previous chapter about refraction of light by lenses. You also studied the nature, position and relative size of images formed by lenses. How can these ideas help us in the study of the human eye?...
Summarize the following historical passage:	Science 12 1.2.5 Oxidation and Reduction Activity 1.11 Activity 1.11 Activity 1.11 Activity 1.11 Activity 1.11 n Heat a china dish containing about 1 g copper powder (Fig. 1.10). n What do you observe? Figure 1.10 Figure 1.10 Figure 1.10 Figure 1.10 Figure 1.10 Oxidation of copper to copper oxide The surface of copper powder becomes coated with black copper(II) oxide. Why has this black substance formed? This is because oxygen is added to copper and copper oxide is formed. 2Cu + O2 Heat  → 2CuO (1.28) If hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained. CuO +H Cu+H O 2 2 Heat  →  (1.29) If a substance gains oxygen during a reaction, it is said to be oxidised. If a substance loses oxygen during a reaction, it is said to be reduced. During this reaction (1.29), the copper(II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidised. In other words, one reactant gets oxidised while the other gets reduced during a reaction. Such reactions are called oxidation-reduction reactions or redox reactions. (1.30) Some other examples of redox reactions are: ZnO + C → + Zn CO (1.31) MnO HCl MnCl H O Cl 2 2 2 2 4 2 + → + + (1.32) Recall Activity 1.2 Recall Activity 1.2 Recall Activity 1.2 Recall Activity 1.2 Recall Activity 1.2, where you have mixed the solutions of lead(II) nitrate and potassium iodide. (i) What was the colour of the precipitate formed? Can you name the compound precipitated? (ii) Write the balanced chemical equation for this reaction. (iii) Is this also a double displacement reaction? What causes this? The white precipitate of BaSO4 is formed by the reaction of 2– 4 SO and Ba2+. The other product formed is sodium chloride which remains in the solution. Such reactions in which there is an exchange of ions between the reactants are called double displacement reactions. 2024-25	Science 12 1.2.5 Oxidation and Reduction Activity 1.11 Activity 1.11 Activity 1.11 Activity 1.11 Activity 1.11 n Heat a china dish containing about 1 g copper powder (Fig. 1.10). n What do you observe? Figure 1.10 Figure 1.10 Figure 1.10 Figure 1.10 Figure 1.10 Oxidation of copper to copper oxide...
Summarize the following historical passage:	Metals and Non-metals 57 8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte? 9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below. (a) What will be the action of gas on (i) dry litmus paper? (ii) moist litmus paper? (b) Write a balanced chemical equation for the reaction taking place. 10. State two ways to prevent the rusting of iron. 11. What type of oxides are formed when non-metals combine with oxygen? 12. Give reasons (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction. 13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels. 14. Differentiate between metal and non-metal on the basis of their chemical properties. 15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used? 16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron). Collection of gas 2024-25	Metals and Non-metals 57 8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte? 9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown...
Summarize the following historical passage:	Science 120 reproduction incorporates such a process of combining DNA from two different individuals during reproduction. But this creates a major difficulty. If each new generation is to be the combination of the DNA copies from two pre-existing individuals, then each new generation will end up having twice the amount of DNA that the previous generation had. This is likely to mess up the control of the cellular apparatus by the DNA. How many ways can we think of for solving this difficulty? We have seen earlier that as organisms become more complex, the specialisation of tissue increases. One solution that many multi-cellular organisms have found for the problem mentioned above is to have special lineages of cells in specialised organs in which only half the number of chromosomes and half the amount of DNA as compared to the non- reproductive body cells. This is achieved by a process of cell division called meiosis. Thus, when these germ-cells from two individuals combine during sexual reproduction to form a new individual, it results in re- establishment of the number of chromosomes and the DNA content in the new generation. If the zygote is to grow and develop into an organism which has highly specialised tissues and organs, then it has to have sufficient stores of energy for doing this. In very simple organisms, it is seen that the two germ-cells are not very different from one another, or may even be similar. But as the body designs become more complex, the germ-cells also specialise. One germ-cell is large and contains the food-stores while the other is smaller and likely to be motile. Conventionally, the motile germ- cell is called the male gamete and the germ-cell containing the stored food is called the female gamete. We shall see in the next few sections how the need to create these two different types of gametes give rise to differences in the male and female reproductive organs and, in some cases, differences in the bodies of the male and female organisms. 7.3.2 Sexual Reproduction in Flowering Plants The reproductive parts of angiosperms are located in the flower. You have already studied the different parts of a flower – sepals, petals, stamens and pistil. Stamens and pistil are the reproductive parts of a flower which contain the germ-cells. What possible functions could the petals and sepals serve? The flower may be unisexual (papaya, watermelon) when it contains either stamens or pistil or bisexual (Hibiscus, mustard) when it contains both stamens and pistil. Stamen is the male reproductive part and it produces pollen grains that are yellowish in colour. You must have seen this yellowish powder that often sticks to our hands if we touch the stamen of a flower. Pistil is present in the centre of a flower and is the female reproductive part. It is made of three parts. Figure 7.7 Figure 7.7 Figure 7.7 Figure 7.7 Figure 7.7 Longitudinal section of flower 2024-25	Science 120 reproduction incorporates such a process of combining DNA from two different individuals during reproduction. But this creates a major difficulty. If each new generation is to be the combination of the DNA copies from two pre-existing individuals, then each new generation will end up having twice the amount...
Summarize the following historical passage:	ρ = 1 4 l A R2 1 = 4 R1 R2= 1Ω The resistance of the new wire is 1Ω. 2024-25	ρ = 1 4 l A R2 1 = 4 R1 R2= 1Ω The resistance of the new wire is 1Ω. 2024-25...
Summarize the following historical passage:	Chemical Reactions and Equations 13 In reaction (1.31) carbon is oxidised to CO and ZnO is reduced to Zn. In reaction (1.32) HCl is oxidised to Cl2 whereas MnO2 is reduced to MnCl2. From the above examples we can say that if a substance gains oxygen or loses hydrogen during a reaction, it is oxidised. If a substance loses oxygen or gains hydrogen during a reaction, it is reduced. Q U E S T I O N S ? 1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it? 2. Give an example of a double displacement reaction other than the one given in Activity 1.10. 3. Identify the substances that are oxidised and the substances that are reduced in the following reactions. (i) 4Na(s) + O2(g) → 2Na2O(s) (ii) CuO(s) + H2(g) → Cu(s) + H2O(l) 1.3 1.3 1.3 1.3 1.3 HA HA HA HA HAVE YOU OBSERVED THE EFFECTS OF O VE YOU OBSERVED THE EFFECTS OF O VE YOU OBSERVED THE EFFECTS OF O VE YOU OBSERVED THE EFFECTS OF O VE YOU OBSERVED THE EFFECTS OF OXID XID XID XID XIDAAAAATION TION TION TION TION REA REA REA REA REACTIONS IN EVERYD CTIONS IN EVERYD CTIONS IN EVERYD CTIONS IN EVERYD CTIONS IN EVERYDAAAAAY LIFE? Y LIFE? Y LIFE? Y LIFE? Y LIFE? 1.3.1 Corrosion You must have observed that iron articles are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. Some other metals also get tarnished in this manner. Have you noticed the colour of the coating formed on copper and silver? When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. The black coating on silver and the green coating on copper are other examples of corrosion. Corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals, specially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron. You will learn more about corrosion in Chapter 3. 1.3.2 Rancidity Have you ever tasted or smelt the fat/oil containing food materials left for a long time? When fats and oils are oxidised, they become rancid and their smell and taste change. Usually substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. Keeping food in air tight containers helps to slow down oxidation. Do you know that chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised ? Recall Activity 1.1 Recall Activity 1.1 Recall Activity 1.1 Recall Activity 1.1 Recall Activity 1.1, where a magnesium ribbon burns with a dazzling flame in air (oxygen) and changes into a white substance, magnesium oxide. Is magnesium being oxidised or reduced in this reaction? 2024-25	Chemical Reactions and Equations 13 In reaction (1.31) carbon is oxidised to CO and ZnO is reduced to Zn. In reaction (1.32) HCl is oxidised to Cl2 whereas MnO2 is reduced to MnCl2. From the above examples we can say that if a substance gains oxygen or loses hydrogen during...
Summarize the following historical passage:	Science 26 Activity 2.11 Activity 2.11 Activity 2.11 Activity 2.11 Activity 2.11 n Test the pH values of solutions given in Table 2.2. n Record your observations. n What is the nature of each substance on the basis of your observations? Figure 2.7 Figure 2.7 Figure 2.7 Figure 2.7 Figure 2.7 pH of some common substances shown on a pH paper (colours are only a rough guide) The strength of acids and bases depends on the number of H+ ions and OH– ions produced, respectively. If we take hydrochloric acid and acetic acid of the same concentration, say one molar, then these produce different amounts of hydrogen ions. Acids that give rise to more H+ ions are said to be strong acids, and acids that give less H+ ions are said to be weak acids. Can you now say what weak and strong bases are? 2.3.1 Impor 2.3.1 Impor 2.3.1 Impor 2.3.1 Impor 2.3.1 Importance of pH in Ever tance of pH in Ever tance of pH in Ever tance of pH in Ever tance of pH in Everyday Life yday Life yday Life yday Life yday Life Are plants and animals pH sensitive? Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult. Table 2.2 S. Solution Colour of Approx- Nature of No. pH paper -imate substance pH value 1 Saliva (before meal) 2 Saliva (after meal) 3 Lemon juice 4 Colourless aerated drink 5 Carrot juice 6 Coffee 7 Tomato juice 8 Tap water 9 1M NaOH 10 1M HCl 2024-25	Science 26 Activity 2.11 Activity 2.11 Activity 2.11 Activity 2.11 Activity 2.11 n Test the pH values of solutions given in Table 2.2. n Record your observations. n What is the nature of each substance on the basis of your observations? Figure 2.7 Figure 2.7 Figure 2.7 Figure 2.7 Figure...
Summarize the following historical passage:	Science 214 We have seen in the chapter on ‘Life Processes’ that the food we eat is digested by various enzymes in our body. Have you ever wondered why the same enzyme does not break-down everything we eat? Enzymes are specific in their action, specific enzymes are needed for the break-down of a particular substance. That is why we will not get any energy if we try to eat coal! Because of this, many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time. Substances that are broken down by biological processes are said to be biodegradable. How many of the substances you buried were biodegradable? Substances that are not broken down in this manner are said to be non-biodegradable. These substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system. Activity 13.6 Activity 13.6 Activity 13.6 Activity 13.6 Activity 13.6 n Use the library or internet to find out more about biodegradable and non-biodegradable substances. n How long are various non-biodegradable substances expected to last in our environment? n These days, new types of plastics which are said to be biodegradable are available. Find out more about such materials and whether they do or do not harm the environment. 1. Why are some substances biodegradable and some non-biodegradable? 2. Give any two ways in which biodegradable substances would affect the environment. 3. Give any two ways in which non-biodegradable substances would affect the environment. Q U E S T I O N S ? Visit any town or city, and we are sure to find heaps of garbage all over the place. Visit any place of tourist interest and we are sure to find the place littered with empty food wrappers. In the earlier classes we have talked about this problem of dealing with the garbage that we generate. Let us now look at the problem a bit more deeply. 2024-25	Science 214 We have seen in the chapter on ‘Life Processes’ that the food we eat is digested by various enzymes in our body. Have you ever wondered why the same enzyme does not break-down everything we eat? Enzymes are specific in their action, specific enzymes are needed for the...
Summarize the following historical passage:	Science 20 Note that the metal in the above reactions displaces hydrogen atoms from the acids as hydrogen gas and forms a compound called a salt. Thus, the reaction of a metal with an acid can be summarised as – Acid + Metal → Salt + Hydrogen gas Can you now write the equations for the reactions you have observed? Activity 2.4 Activity 2.4 Activity 2.4 Activity 2.4 Activity 2.4 The reactions occurring in the above Activity are written as – Test tube A: Na CO HCl(aq) Cl(aq) H O(l) + CO 2 3 2 2 (s) Na (g) + → + 2 2 Test tube B: NaHCO HCl(aq) Cl(aq) H O(l) + CO 3 2 2 (s) Na (g) + → + On passing the carbon dioxide gas evolved through lime water, Ca(OH) CO H O(l) 2 2 2 (aq) (g) CaCO s 3 + → + ( ) (Lime water) (White precipitate) n Place a few pieces of granulated zinc metal in a test tube. n Add 2 mL of sodium hydroxide solution and warm the contents of the test tube. n Repeat the rest of the steps as in Activity 2.3 and record your observations. The reaction that takes place can be written as follows. 2NaOH(aq) + Zn(s) → Na2ZnO2(s) + H2(g) (Sodium zincate) You find again that hydrogen is formed in the reaction. However, such reactions are not possible with all metals. 2.1.3 How do Metal Carbonates and Metal Hydrogencarbonates React with Acids? Activity 2.5 Activity 2.5 Activity 2.5 Activity 2.5 Activity 2.5 n Take two test tubes, label them as A and B. n Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A and about 0.5 g of sodium hydrogencarbonate (NaHCO3) in test tube B. n Add about 2 mL of dilute HCl to both the test tubes. n What do you observe? n Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in Fig. 2.2 and record your observations. Figure 2.2 Figure 2.2 Figure 2.2 Figure 2.2 Figure 2.2 Passing carbon dioxide gas through calcium hydroxide solution 2024-25	Science 20 Note that the metal in the above reactions displaces hydrogen atoms from the acids as hydrogen gas and forms a compound called a salt. Thus, the reaction of a metal with an acid can be summarised as – Acid + Metal → Salt + Hydrogen gas Can you...
Summarize the following historical passage:	Metals and Non-metals 51 used for removing the gangue from the ore are based on the differences between the physical or chemical properties of the gangue and the ore. Different separation techniques are accordingly employed. 3.4.3 Extracting Metals Low in the Activity Series Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone. For example, cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating. 2HgS(s) + 3O (g) 2HgO(s) + 2SO (g) 2 2 Heat  →  2HgO(s) 2Hg(l) + O (g) 2 Heat  →  Similarly, copper which is found as Cu2S in nature can be obtained from its ore by just heating in air. 2Cu S + 3O (g) 2Cu O(s) + 2SO (g) 2Cu O + Cu S 2 2 2 2 2 2 Heat Heat  →   → 6Cu(s) + SO (g) 2 3.4.4 Extracting Metals in the Middle of the Activity Series The metals in the middle of the activity series such as iron, zinc, lead, copper, are moderately reactive. These are usually present as sulphides or carbonates in nature. It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides. The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting. The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows – Roasting 2ZnS(s) + 3O (g) 2ZnO(s) + 2SO (g) 2 2 Heat  →  Calcination ZnCO (s) ZnO(s) + CO (g) 3 2 Heat  →  The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc. ZnO(s) + C(s) → Zn(s) + CO(g) You are already familiar with the process of oxidation and reduction explained in the first Chapter. Obtaining metals from their compounds is also a reduction process. Besides using carbon (coke) to reduce metal oxides to metals, sometimes displacement reactions can also be used. The highly reactive metals such as sodium, calcium, aluminium, etc., are used as reducing 2024-25	Metals and Non-metals 51 used for removing the gangue from the ore are based on the differences between the physical or chemical properties of the gangue and the ore. Different separation techniques are accordingly employed. 3.4.3 Extracting Metals Low in the Activity Series Metals low in the activity series are...
Summarize the following historical passage:	Science 24 KOH(s) K (aq)+OH (aq) H O 2 +  →  – Mg(OH)2(s) H O 2  → Mg2+(aq)+2OH–(aq) Bases generate hydroxide (OH–) ions in water. Bases which are soluble in water are called alkalis. Do You Know? All bases do not dissolve in water. An alkali is a base that dissolves in water. They are soapy to touch, bitter and corrosive. Never taste or touch them as they may cause harm. Which of the bases in the Table 2.1 are alkalis? Now as we have identified that all acids generate H+(aq) and all bases generate OH –(aq), we can view the neutralisation reaction as follows – Acid + Base → Salt + Water H X + M OH → MX + HOH H+(aq) + OH – (aq) → H2O(l) Let us see what is involved when water is mixed with an acid or a base. Activity 2.10 Activity 2.10 Activity 2.10 Activity 2.10 Activity 2.10 n Take 10 mL water in a beaker. n Add a few drops of concentrated H2SO4 to it and swirl the beaker slowly. n Touch the base of the beaker. n Is there a change in temperature? n Is this an exothermic or endothermic process? n Repeat the above Activity with sodium hydroxide pellets and record your observations. Figure 2.5 Figure 2.5 Figure 2.5 Figure 2.5 Figure 2.5 Warning sign displayed on containers containing concentrated acids and bases The process of dissolving an acid or a base in water is a highly exothermic one. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating. Look out for the warning sign (shown in Fig. 2.5) on the can of concentrated sulphuric acid and on the bottle of sodium hydroxide pellets. Mixing an acid or base with water results in decrease in the concentration of ions (H3O+/OH–) per unit volume. Such a process is called dilution and the acid or the base is said to be diluted. 2024-25	Science 24 KOH(s) K (aq)+OH (aq) H O 2 +  →  – Mg(OH)2(s) H O 2  → Mg2+(aq)+2OH–(aq) Bases generate hydroxide (OH–) ions in water. Bases which are soluble in water are called alkalis. Do You Know? All bases do not dissolve in water. An alkali is...
Summarize the following historical passage:	Acids, Bases and Salts 27 What is the pH of the soil in your backyard? Plants require a specific pH range for their healthy growth. To find out the pH required for the healthy growth of a plant, you can collect the soil from various places and check the pH in the manner described below in Activity 2.12. Also, you can note down which plants are growing in the region from which you have collected the soil. Acids in other planets The atmosphere of venus is made up of thick white and yellowish clouds of sulphuric acid. Do you think life can exist on this planet? Activity 2.12 Activity 2.12 Activity 2.12 Activity 2.12 Activity 2.12 n Put about 2 g soil in a test tube and add 5 mL water to it. n Shake the contents of the test tube. n Filter the contents and collect the filtrate in a test tube. n Check the pH of this filtrate with the help of universal indicator paper. n What can you conclude about the ideal soil pH for the growth of plants in your region? pH in our digestive system It is very interesting to note that our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids. One such remedy must have been suggested by you at the beginning of this Chapter. These antacids neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose. pH change as the cause of tooth decay Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay. Self defence by animals and plants through chemical warfare Have you ever been stung by a honey-bee? Bee-sting leaves an acid which causes pain and irritation. Use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves inject methanoic acid causing burning pain. Do You Know? 2024-25	Acids, Bases and Salts 27 What is the pH of the soil in your backyard? Plants require a specific pH range for their healthy growth. To find out the pH required for the healthy growth of a plant, you can collect the soil from various places and check the pH...
Summarize the following historical passage:	Science 84 taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen. 5.2.2 Heterotrophic Nutrition Each organism is adapted to its environment. The form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organism. For example, whether the food source is stationary (such as grass) or mobile (such as a deer), would allow for differences in how the food is accessed and what is the nutritive apparatus used by a cow and a lion. There is a range of strategies by which the food is taken in and used by the organism. Some organisms break-down the food material outside the body and then absorb it. Examples are fungi like bread moulds, yeast and mushrooms. Others take in whole material and break it down inside their bodies. What can be taken in and broken down depends on the body design and functioning. Some other organisms derive nutrition from plants or animals without killing them. This parasitic nutritive strategy is used by a wide variety of organisms like cuscuta (amar-bel), ticks, lice, leeches and tape-worms. 5.2.3 How do Organisms obtain their Nutrition? Since the food and the way it is obtained differ, the digestive system is different in various organisms. In single-celled organisms, the food may be taken in by the entire surface. But as the complexity of the organism increases, different parts become specialised to perform different functions. For example, Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole (Fig. 5.5). Inside the food- vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out. In Paramoecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell. 5.2.4 Nutrition in Human Beings The alimentary canal is basically a long tube extending from the mouth to the anus. In Fig. 5.6, we can see that the tube has different parts. Various regions are specialised to perform different functions. What happens to the food once it enters our body? We shall discuss this process here. Figure 5.5 Figure 5.5 Figure 5.5 Figure 5.5 Figure 5.5 Nutrition in Amoeba 2024-25	Science 84 taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen. 5.2.2 Heterotrophic Nutrition Each organism is adapted to its environment. The form of nutrition differs depending on the type and availability...
Summarize the following historical passage:	(xi) CONTENTS Foreword iii Rationalisation of Content in the Textbooks v Preface vii Chapter 1 Chemical Reactions and Equations 1 Chapter 2 Acids, Bases and Salts 17 Chapter 3 Metals and Non-metals 37 Chapter 4 Carbon and its Compounds 58 Chapter 5 Life Processes 79 Chapter 6 Control and Coordination 100 Chapter 7 How do Organisms Reproduce? 113 Chapter 8 Heredity 128 Chapter 9 Light – Reflection and Refraction 134 Chapter 10 The Human Eye and the Colourful World 161 Chapter 11 Electricity 171 Chapter 12 Magnetic Effects of Electric Current 195 Chapter 13 Our Environment 208 Answers 218-219 CONTENTS 2024-25	(xi) CONTENTS Foreword iii Rationalisation of Content in the Textbooks v Preface vii Chapter 1 Chemical Reactions and Equations 1 Chapter 2 Acids, Bases and Salts 17 Chapter 3 Metals and Non-metals 37 Chapter 4 Carbon and its Compounds 58 Chapter 5 Life Processes 79 Chapter 6 Control and Coordination...
Summarize the following historical passage:	How do Organisms Reproduce? 117 Figure 7.3 Figure 7.3 Figure 7.3 Figure 7.3 Figure 7.3 Regeneration in Planaria take place in an organised sequence referred to as development. However, regeneration is not the same as reproduction, since most organisms would not normally depend on being cut up to be able to reproduce. 7.2.4 Budding Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site (Fig. 7.4). These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals. Figure 7.4 Figure 7.4 Figure 7.4 Figure 7.4 Figure 7.4 Budding in Hydra 7.2.5 Vegetative Propagation There are many plants in which parts like the root, stem and leaves develop into new plants under appropriate conditions. Unlike in most animals, plants can indeed use such a mode for reproduction. This property of vegetative propagation is used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes. Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds. Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its characteristics. 2024-25	How do Organisms Reproduce? 117 Figure 7.3 Figure 7.3 Figure 7.3 Figure 7.3 Figure 7.3 Regeneration in Planaria take place in an organised sequence referred to as development. However, regeneration is not the same as reproduction, since most organisms would not normally depend on being cut up to be able...
Summarize the following historical passage:	Light – Reflection and Refraction 155 Figure 9.16 Figure 9.16 Figure 9.16 Figure 9.16 Figure 9.16 The position, size and the nature of the image formed by a convex lens for various positions of the object Figure 9.17 Figure 9.17 Figure 9.17 Figure 9.17 Figure 9.17 Nature, position and relative size of the image formed by a concave lens 9.3.6 Sign Convention for Spherical Lenses For lenses, we follow sign convention, similar to the one used for spherical mirrors. We apply the rules for signs of distances, except that all measurements are taken from the optical centre of the lens. According to the convention, the focal length of a convex lens is positive and that of a concave lens is negative. You must take care to apply appropriate signs for the values of u, v, f, object height h and image height h′. 9.3.7 Lens Formula and Magnification As we have a formula for spherical mirrors, we also have formula for spherical lenses. This formula gives the relationship between object- distance (u), image-distance (v) and the focal length (f ). The lens formula is expressed as 1 1 1 v u f − = (9.8) The lens formula given above is general and is valid in all situations for any spherical lens. Take proper care of the signs of different quantities, while putting numerical values for solving problems relating to lenses. 2024-25	Light – Reflection and Refraction 155 Figure 9.16 Figure 9.16 Figure 9.16 Figure 9.16 Figure 9.16 The position, size and the nature of the image formed by a convex lens for various positions of the object Figure 9.17 Figure 9.17 Figure 9.17 Figure 9.17 Figure 9.17 Nature, position and relative...
Summarize the following historical passage:	Light – Reflection and Refraction 139 (ii) A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror, after reflection, will emerge parallel to the principal axis. This is illustrated in Fig.9.4 (a) and (b). (iii) A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror, after reflection, is reflected back along the same path. This is illustrated in Fig.9.5 (a) and (b). The light rays come back along the same path because the incident rays fall on the mirror along the normal to the reflecting surface. (iv) A ray incident obliquely to the principal axis, towards a point P (pole of the mirror), on the concave mirror [Fig. 9.6 (a)] or a convex mirror [Fig. 9.6 (b)], is reflected obliquely. The incident and reflected rays follow the laws of reflection at the point of incidence (point P), making equal angles with the principal axis. (a) (b) Figure 9.4 Figure 9.4 Figure 9.4 Figure 9.4 Figure 9.4 Remember that in all the above cases the laws of reflection are followed. At the point of incidence, the incident ray is reflected in such a way that the angle of reflection equals the angle of incidence. (a) Image formation by Concave Mirror Figure 9.7 illustrates the ray diagrams for the formation of image by a concave mirror for various positions of the object. (b) (a) Figure 9.5 Figure 9.5 Figure 9.5 Figure 9.5 Figure 9.5 (a) (b) Figure 9.6 Figure 9.6 Figure 9.6 Figure 9.6 Figure 9.6 2024-25	Light – Reflection and Refraction 139 (ii) A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror, after reflection, will emerge parallel to the principal axis. This is illustrated in Fig.9.4 (a) and (b). (iii)...
Summarize the following historical passage:	Science 74 CH COOC H C H OH+CH COONa 3 2 5 2 5 3 NaOH (ii) Reaction with a base: Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate or commonly called sodium acetate) and water: NaOH + CH3COOH → CH3COONa + H2O How does ethanoic acid react with carbonates and hydrogencarbonates? Let us perform an activity to find out. Activity 4.9 Activity 4.9 Activity 4.9 Activity 4.9 Activity 4.9 n Set up the apparatus as shown in Chapter 2, Activity 2.5. n Take a spatula full of sodium carbonate in a test tube and add 2 mL of dilute ethanoic acid. n What do you observe? n Pass the gas produced through freshly prepared lime-water. What do you observe? n Can the gas produced by the reaction between ethanoic acid and sodium carbonate be identified by this test? n Repeat this Activity with sodium hydrogencarbonate instead of sodium carbonate. (iii) Reaction with carbonates and hydrogencarbonates: Ethanoic acid reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide and water. The salt produced is commonly called sodium acetate. 2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2 CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 Q U E S T I O N S 1. How would you distinguish experimentally between an alcohol and a carboxylic acid? 2. What are oxidising agents? 4.5 SOAPS AND DETERGENTS Activity 4.10 Activity 4.10 Activity 4.10 Activity 4.10 Activity 4.10 n Take about 10 mL of water each in two test tubes. n Add a drop of oil (cooking oil) to both the test tubes and label them as A and B. n To test tube B, add a few drops of soap solution. n Now shake both the test tubes vigourously for the same period of time. n Can you see the oil and water layers separately in both the test tubes immediately after you stop shaking them? n Leave the test tubes undisturbed for some time and observe. Does the oil layer separate out? In which test tube does this happen first? Figure 4.12 Figure 4.12 Figure 4.12 Figure 4.12 Figure 4.12 Formation of micelles ? 2024-25	Science 74 CH COOC H C H OH+CH COONa 3 2 5 2 5 3 NaOH (ii) Reaction with a base: Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate or commonly called sodium acetate) and water: NaOH + CH3COOH...
Summarize the following historical passage:	Carbon and its Compounds 67 unit? Do you see any relation between the number of carbon and hydrogen atoms in these compounds? The general formula for alkenes can be written as CnH2n, where n = 2, 3, 4. Can you similarly generate the general formula for alkanes and alkynes? As the molecular mass increases in any homologous series, a gradation in physical properties is seen. This is because the melting and boiling points increase with increasing molecular mass. Other physical properties such as solubility in a particular solvent also show a similar gradation. But the chemical properties, which are determined solely by the functional group, remain similar in a homologous series. Activity 4.2 Activity 4.2 Activity 4.2 Activity 4.2 Activity 4.2 4.2.5 Nomenclature of Carbon Compounds The names of compounds in a homologous series are based on the name of the basic carbon chain modified by a “prefix” “phrase before” or “suffix” “phrase after” indicating the nature of the functional group. For example, the names of the alcohols taken in Activity 4.2 are methanol, ethanol, propanol and butanol. Naming a carbon compound can be done by the following method – (i) Identify the number of carbon atoms in the compound. A compound having three carbon atoms would have the name propane. (ii) In case a functional group is present, it is indicated in the name of the compound with either a prefix or a suffix (as given in Table 4.4). (iii) If the name of the functional group is to be given as a suffix, and the suffix of the functional group begins with a vowel a, e, i, o, u, then the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would be named in the following manner – Propane – ‘e’ = propan + ‘one’ = propanone. (iv) If the carbon chain is unsaturated, then the final ‘ane’ in the name of the carbon chain is substituted by ‘ene’ or ‘yne’ as given in Table 4.4. For example, a three-carbon chain with a double bond would be called propene and if it has a triple bond, it would be called propyne. n Calculate the difference in the formulae and molecular masses for (a) CH3OH and C2H5OH (b) C2H5OH and C3H7OH, and (c) C3H7OH and C4H9OH. n Is there any similarity in these three? n Arrange these alcohols in the order of increasing carbon atoms to get a family. Can we call this family a homologous series? n Generate the homologous series for compounds containing up to four carbons for the other functional groups given in Table 4.3. 2024-25	Carbon and its Compounds 67 unit? Do you see any relation between the number of carbon and hydrogen atoms in these compounds? The general formula for alkenes can be written as CnH2n, where n = 2, 3, 4. Can you similarly generate the general formula for alkanes and alkynes? As...
Summarize the following historical passage:	Science 124 When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube. The two oviducts unite into an elastic bag-like structure known as the uterus. The uterus opens into the vagina through the cervix. The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg. The fertilised egg (zygote) starts dividing and form a ball of cells or embryo. The embryo is implanted in the lining of the uterus where they continue to grow and develop organs to become foetus. We have seen in earlier sections that the mother’s body is designed to undertake the development of the child. Hence the uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta. The development of the child inside the mother’s body takes approximately nine months. The child is born as a result of rhythmic contractions of the muscles in the uterus. 7.3.3 (c) What happens when the Egg is not Fertilised? If the egg is not fertilised, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. Thus its lining becomes thick and spongy. This would be required for nourishing the embryo if fertilisation had taken place. Now, however, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days. 7.3.3 (d) Reproductive Health As we have seen, the process of sexual maturation is gradual, and takes place while general body growth is still going on. Therefore, some degree of sexual maturation does not necessarily mean that the body or the mind is ready for sexual acts or for having and bringing up children. How do we decide if the body or the mind is ready for this major responsibility? All of us are under many different kinds of pressures about these issues. There can be pressure from our friends for participating in many activities, whether we really want to or not. There can be pressure from families to get married and start having children. There can be pressure from government agencies to avoid having children. In this situation, making choices can become very difficult. 2024-25	Science 124 When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian...
Summarize the following historical passage:	Science 28 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SALTS TS TS TS TS In the previous sections we have seen the formation of salts during various reactions. Let us understand more about their preparation, properties and uses. 2.4.1 Family of Salts Activity 2.13 Activity 2.13 Activity 2.13 Activity 2.13 Activity 2.13 n Write the chemical formulae of the salts given below. Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride. Nature provides neutralisation options Nettle is a herbaceous plant which grows in the wild. Its leaves have stinging hair, which cause painful stings when touched accidentally. This is due to the methanoic acid secreted by them. A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle in the wild. Can you guess the nature of the dock plant? So next time you know what to look out for if you accidentally touch a nettle plant while trekking. Are you aware of any other effective traditional remedies for such stings? Table 2.3 Some naturally occurring acids Natural source Acid Natural source Acid Vinegar Acetic acid Sour milk (Curd) Lactic acid Orange Citric acid Lemon Citric acid Tamarind Tartaric acid Ant sting Methanoic acid Tomato Oxalic acid Nettle sting Methanoic acid Q U E S T I O N S 1. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic? 2. What effect does the concentration of H+(aq) ions have on the nature of the solution? 3. Do basic solutions also have H+(aq) ions? If yes, then why are these basic? 4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)? ? Do You Know? 2024-25	Science 28 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SAL 2.4 MORE ABOUT SALTS TS TS TS TS In the previous sections we have seen the formation of salts during various reactions. Let us understand more about their preparation, properties and uses....
Summarize the following historical passage:	Chemical Reactions and Equations 3 1.1.1 Writing a Chemical Equation Is there any other shorter way for representing chemical equations? Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equation represents a chemical reaction. If you recall formulae of magnesium, oxygen and magnesium oxide, the above word-equation can be written as – Mg + O2 → MgO (1.2) Count and compare the number of atoms of each element on the LHS and RHS of the arrow. Is the number of atoms of each element the same on both the sides? If yes, then the equation is balanced. If not, then the equation is unbalanced because the mass is not the same on both sides of the equation. Such a chemical equation is a skeletal chemical equation for a reaction. Equation (1.2) is a skeletal chemical equation for the burning of magnesium in air. 1.1.2 Balanced Chemical Equations Recall the law of conservation of mass that you studied in Class IX; mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation. Is the chemical Eq. (1.2) balanced? Let us learn about balancing a chemical equation step by step. The word-equation for Activity 1.3 may be represented as – Zinc + Sulphuric acid → Zinc sulphate + Hydrogen The above word-equation may be represented by the following chemical equation – Zn + H2SO4 → ZnSO4 + H2 (1.3) Let us examine the number of atoms of different elements on both sides of the arrow. Element Number of atoms in Number of atoms reactants (LHS) in products (RHS) Zn 1 1 H 2 2 S 1 1 O 4 4 As the number of atoms of each element is the same on both sides of the arrow, Eq. (1.3) is a balanced chemical equation. Let us try to balance the following chemical equation – Fe + H2O → Fe3O4 + H2 (1.4) 2024-25	Chemical Reactions and Equations 3 1.1.1 Writing a Chemical Equation Is there any other shorter way for representing chemical equations? Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equation represents a chemical reaction. If you recall formulae of magnesium,...