{"id":19443,"date":"2018-08-24T07:15:19","date_gmt":"2018-08-24T07:15:19","guid":{"rendered":"https:\/\/www.aplustopper.com\/?p=19443"},"modified":"2020-12-04T10:24:51","modified_gmt":"2020-12-04T04:54:51","slug":"selina-icse-solutions-class-9-chemistry-water","status":"publish","type":"post","link":"https:\/\/www.aplustopper.com\/selina-icse-solutions-class-9-chemistry-water\/","title":{"rendered":"Selina Concise Chemistry Class 9 ICSE Solutions Water"},"content":{"rendered":"
ICSE Solutions<\/a>Selina ICSE Solutions<\/a><\/p>\n APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Chemistry Chapter 3 Water. You can download the Selina Concise Chemistry ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Chemistry for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.<\/p>\n Exercise 6(A)<\/strong><\/span><\/p>\n Question 1. Question 2. Question 3. (b) Our body is almost 65% of water and water has property of specific heat. Due high specific heat capacity the presence of large amount of water is able to modify the climate of the body and control the temperature of our body which is warm in winter and cooler in summer.<\/p>\n Question 4. Question 5. Question 6. (C) Melting point:\u00a0<\/strong>The constant temperature at which a solid changes into a liquid state, by absorbing the heat energy is called melting point.<\/p>\n Boiling point:\u00a0<\/strong>The temperature at which water starts boiling under normal pressure is called boiling point of water.” It is 100\u00b0C. Boiling point increases with increase in pressure and vice versa.”<\/p>\n Specific heat capacity:\u00a0<\/strong>The amount of heat required to raise the temperature of unit mass of that substance through 1\u00b0C.<\/p>\n Latent heat of vaporization of water:\u00a0<\/strong>The energy required to change water into its\u00a0vapour\u00a0at its boiling point without any change in temperature is called latent heat of vaporization of water.<\/p>\n Latent heat of vaporization of water is 2260 joules J\/g or 540 cal\/g. Question 7. Question 8. Question 9. Solution 10.<\/strong><\/span><\/p>\n (a)\u00a0Aim<\/strong>: <\/strong>To show that tap water contains dissolved salts.<\/p>\n Procedure:<\/strong> Put some tap water on a clean watch glass and place it over a beaker containing water as shown in fig. Boil the water in the beaker. When all the water has evaporated from the watch glass, remove the burner and let it cool. We see at the watch glass against light, a number of concentric rings of solids matter on it. These are dissolved impurities, left behind after evaporation of water. To show that water contains dissolved solids.<\/p>\n <\/p>\n (b) Aim:<\/strong> To show that tap water contains dissolved gases.<\/p>\n Procedure:\u00a0<\/strong>Take a round bottomed flask and filled it with the tap water. In its mouth fix a delivery tube, in such a way that its lower end of the delivery tube is in line with the under – surface of the cork.<\/p>\n Arrange the apparatus according to diagram.<\/p>\n Heat the flask with the help of a Bunsen burner. It is seen that tiny bubbles of gas are coming out, which stick to the sides of flask, heat it continuously, till the water is about to boil. It is seen that Bubbles of gas start coming out of beehive shelf.<\/p>\n Now lower the flame, to keep the water just near its boiling point. Invert over the beehive shelf a graduated tube, completely filled with tap water. Gradually, the boiled off air, starts collecting in the flask. Collect at least two tubes of boiled off air.<\/p>\n <\/p>\n Question 11. Question 12. Solution 13.<\/strong><\/span><\/p>\n Rivers and lakes have large amount of water and water has high specific heat capacity, due to which they do not freeze easily. Question 14. Question 15. (b) Ice at zero degree centigrade gives more cooling effect than water at 0\u00b0C because, ice at 0\u00b0C absorbs 336J per gram of energy to melt to 0\u00b0C water and hence gives more cooling effect.<\/p>\n (c) Burn caused by steam is more severe than burn caused by boiling water because, 1 g of steam contains 2268J more energy than 1 g of boiling water and hence, cause more severe burns.<\/p>\n (d) Rain water does not leave concentric rings when boiled because rain water does not contain dissolved solid, so it does not form concentric rings.<\/p>\n (e) Air dissolved in water contains a higher percentage of oxygen because, solubility of oxygen in water is more than in air. So, air dissolved in water contains a higher percentage of oxygen.<\/p>\n (f) If distilled water is kept in a sealed bottle for a long time, it leaves etching on the surface of glass because, the substances which are insoluble in water, actually dissolve in minute traces in water. Even when we drink water from a glass, an extremely small amount of glass dissolves in water, so we see the etching on the surface of glass when a long time sealed bottle of distilled water poured into the glass.<\/p>\n Question 16. PAGE NO: 44<\/strong><\/span><\/p>\n Exercise 6(B)<\/strong><\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Stir this mixture with the help of a glass rod and dissolve copper sulphate crystals. Similarly, go on dissolving more of copper sulphate, (1 gram) at a time with constant and vigorous stirring. A stage is reached when no more copper sulphate dissolves. It is called saturated solution at this temperature.<\/p>\n Take this saturated solution of copper sulphate some solution in a test tube and add some copper sulphate crystals. The crystals do not dissolve but settle down. This indicates that the solution is really saturated.<\/p>\n Question 5. (b) In the laboratory, crystals may be obtained by the following methods:<\/p>\n Question 6. Action of heat on iron (II)\u00a0sulphate<\/strong><\/p>\n When iron (II)\u00a0sulphate\u00a0is heated in a test tube, the following observations are made.<\/p>\n Solution 7.<\/strong><\/span><\/p>\n Table salt becomes sticky on exposure during the rainy season because, table salt generally contains a small percentage of Magnesium chloride, as an impurity. Since, these impurities absorb moisture from air due to their deliquescent nature; therefore it gets wet in rainy season and becomes sticky.<\/p>\n Question 8. Question 9. Question 10. Question 11. Solution 12.<\/strong><\/span><\/p>\n A solubility curve is a line graph which shows changes in the solubility of a solute in a given solvent with a change in temperature. Applications:<\/strong><\/p>\n Question 13. Solution:<\/span><\/p>\n 1. Water is an excellent liquid to use in cooling systems\u00a0due to its ability to absorb large quantities of heat i.e. specific heat = 4.2J\/go<\/sup>C, so it is used in cooling system i.e. cooling agent.<\/p>\n 2.\u00a0 A solution is always clear and transparent because in a solution, solid disappeared in water and water has property – cleanliness and transparent. So, the solution is always clean and transparent.<\/p>\n 3. Lakes and rivers do not freeze suddenly in winters due to high specific latent heat of solidification. i.e. the amount of heat released when 1 g of water solidifies to form 1 g of ice at 0\u00b0C. It is about 336 J\/g or 80 cal\/g. Such enormous amount of heat leads to immediate freezing of lakes and rivers in winter.<\/p>\n 4. The component that actually dissolves in a solvent is known as solute. So it can separated from solution by filtration process. But filtration process is applicable only when solute is insoluble in solution. So the solute cannot be separated from solution by filtration.<\/p>\n 5. Fused CaCl2<\/sub>\u00a0or concentrated H2<\/sub>SO4\u00a0<\/sub>is deliquescent in nature absorbs moisture and hence, these are used in desiccators or as drying agent.<\/p>\n 6. Carbon dioxide is dissolved in soda water under pressure. On opening the bottle, the pressure on the surface of water suddenly decreases, therefore, the solubility of CO2<\/sub>\u00a0in water decreases and the gas rapidly bubbles out.<\/p>\n Question 14. Question 15. Question 16. PAGE NO : 45<\/strong><\/span><\/p>\n Question 17. Solution: Solution 18.<\/strong><\/span><\/p>\n <\/p>\n Solution 19.<\/strong><\/span><\/p>\n <\/p>\n Solution 20.<\/strong><\/span><\/p>\n (c) Solubility of salt at 293K<\/p>\n KNO3<\/sub>\u00a0\u2192 32g (d) At 283K lowest solubility is of KNO3<\/sub>\u00a0\u2192 21g<\/p>\n (e) Solubility of most of solids usually increases and of gas and liquid always decreases with rise in temperature.<\/p>\n Solution 21.<\/strong><\/span><\/p>\n (a) Wt. of empty dish = 50 gm (b) Wt. of water = 50 gm Solution 22.<\/strong><\/span><\/p>\n <\/p>\n PAGE NO: 46<\/strong><\/span><\/p>\n Question 1. Solution 1:<\/strong><\/span><\/p>\n Question 2. Solution:<\/span> Question 3. Question 4. Question 5. Question 6. Solution:<\/span> Question 7. Question 8. Question 9.
\nWater exists in all three states. Discuss.
\nSolution:
\n<\/span>In free state, water occurs in three states viz, solid, liquid and gaseous state.<\/p>\n\n
\nWhy is water considered a compound?
\nSolution:
\n<\/span>Water is considered as a compound because it is made up of two elements, hydrogen and oxygen combined in the ratio of 1 : 8 by mass.
\nMass ratio\u00a0of elements H2<\/sub>O
\nH : O,\u00a02 X 1 : 16 X 1\u00a0=\u00a01 : 8
\n(Atomic mass of H = 1, O = 16)
\nAnd also components of water cannot be separated by physical methods but can be separated by electrolysis of water.<\/p>\n
\n(a) Why does temperature in Mumbai and Chennai not fall as low as it does in Delhi?
\n(b) Give the properties of water responsible for controlling the temperature of our body.
\nSolution:
\n<\/span>(a) The temperature in Mumbai and Chennai do not fall as low as in Delhi because Mumbai and Chennai are situated at the bank of the oceans due to high specific heat capacity the presence of a large amount of water is able to modify the climate of the nearby land areas are warmer in winter and cooler in summer temperature does not fall wherever Delhi has not same condition.<\/p>\n
\nWater is the universal solvent’. Comment.
\nSolution:
\n<\/span>Water dissolves many substances forming aqueous solution. It can dissolve solids, liquids and gases. When a solid dissolves in water the solid is said to be solute, the water (the solvent) and the resultant liquid, the solution. So it is said that water is a universal solvent. In other words water can dissolve nearly every substance.<\/p>\n
\nWhat causes the violence associated with torrential rain?
\nSolution:
\n<\/span>The sudden release of the latent heat of condensation causes the violence associated with torrential rain.<\/p>\n
\n(a) Which property of water enables it to modify the climate?
\n(b) Density of water varies with temperature. What are its consequences?
\n(c) What is the effect of impurities present in the water on the melting point and boiling point of water?
\nSolution:
\n<\/span>(a) Specific heat
\n(b) Water has an unusual physical property. When cooled, it first contracts in volume, as do other liquids, but at 4\u00b0C (maximum density), it starts expanding, and continues to do so till the temperature reaches 0\u00b0C, the point at which it freezes into ice.
\nThe property of anomalous expansion of water enables marine life to exist in the colder regions of the world, because even when the water freezes on the top, it is still liquid below the ice layer.
\n<\/p>\n
\nIn the reverse process, 2260 joules of heat is released when 1 g of steam condenses to form 1 g of water at 100\u00b0C.
\nLatent heat of fusion of ice:\u00a0The amount of heat energy required by ice to change into water is called latent heat of fusion of ice.
\nLatent heat of fusion of ice is 336 J\/g or 80 cal\/g.
\nIn the reverse process, 336 joules of heat is released when 1 g of water solidifies to form 1 g of ice at 0\u00b0C.<\/p>\n
\nWhat is the composition of water? In what volume its elements combine?
\nSolution:
\n<\/span>Composition of water :- Hydrogen and Oxygen Volume Ratio = H2<\/sub>\u00a0: O
\n=\u00a02 : 1<\/p>\n
\nThe properties of water are different from the properties of the elements of which it is formed. Discuss.
\nSolution:
\n<\/span>The properties of water are different from the properties of elements from which it is formed<\/strong><\/p>\n\n\n
\n Property<\/strong><\/td>\n Water<\/strong><\/td>\n Elements – Oxygen and Hydrogen<\/strong><\/td>\n<\/tr>\n \n Nature<\/td>\n It is clear,\u00a0colourless,\u00a0odourless, tasteless and transparent liquid.<\/td>\n These are\u00a0colourless,odourless, tasteless and non-poisonous gases.<\/td>\n<\/tr>\n \n Solubility<\/td>\n It can dissolve many things in it and is called universal solvent.<\/td>\n Oxygen and hydrogen are slightly soluble in water.<\/td>\n<\/tr>\n \n Density<\/td>\n Pure water has maximum density at 4\u00b0C.<\/td>\n Oxygen is heavier than air wherever is the lightest of all the known gases.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\nHow is aquatic life benefited by the fact that water has maximum density at 4o<\/sup>C?
\nSolution:
\n<\/span>The property of anomalous expansion of water enables aquatic life to exist because of the water freezes on top of the surface of the water body, but it is still liquid below the ice layer.<\/p>\n
\nState the importance of the suitability of CO2<\/sub>\u00a0and O2<\/sub>\u00a0in water.
\nSolution:
\n<\/span>CO2<\/sub>\u00a0and O2<\/sub>\u00a0add taste to water for drinking purposes.<\/p>\n
\nHow is air dissolved in water different from ordinary air?
\nSolution:
\n<\/span>Oxygen is more soluble in water than nitrogen. Air dissolved in water contains a higher percentage of oxygen. That is, 30% – 35% and in ordinary air it is only 21 %. In this way air dissolved in water is different from ordinary air.<\/p>\n
\nEven if they freeze, they freeze at top layer. There is water below due to Anomalous expansion of water.<\/p>\n
\nWhat is the importance of dissolved salts in water?
\nSolution:
\n<\/span>Importance of dissolved salts in water:<\/p>\n\n
\nExplain why:
\n(a) Boiled or distilled water tastes flat.
\n(b) Ice at zero degrees centigrade has greater cooling effect than water at 0o<\/sup>C.
\n(c) Burns caused by steam are more severe than burns caused by boiling water.
\n(d) Rivers and lakes do not freeze easily?
\n(e) Air dissolved in water contains a higher proportion of oxygen.
\n(f) If distilled water is kept in a sealed bottle for a long time, it leaves etchings on the surface of the glass.
\nRain water does not leave behind concentric rings when boiled.
\nSolution:
\n<\/span>(a) Boiled water tastes flat because boiled water does not contain matter like air, carbon dioxide and other minerals, So the boiled water tastes flat.<\/p>\n
\nExplain what you understand from the following diagram:
\n
\nSolution:
\n<\/span>(i) When solid changes with liquid, it absorbs heat equal to latent heat of fusion and when a liquid changes into solid, it loses heat equal to latent heat of solidification.
\n(ii) When a liquid changes into gas, it absorbs heat equal to latent heat of vaporization and when a gas condenses into liquid, it loses heat equal to latent heat of condensation.<\/p>\n
\nExplain the terms:
\n(a) Solution
\n(b) Solute
\n(c) Solvent
\nSolution:
\n<\/span>(a) Solution:<\/strong> Solution is a homogeneous mixture of two or more substances, components of which cannot be seen separately.
\n(b) Solute:<\/strong> A solute is the substance that dissolves in a solvent to form a solution.
\n(c) Solvent:<\/strong> A solvent is a medium in which the solute dissolves.
\nSolution = Solute + Solvent<\/strong><\/p>\n
\nExplain why a hot saturated solution of potassium nitrate forms crystals as it cools.
\nSolution:
\n<\/strong><\/span>The solubility of nitrate decreases with the fall in temperature. Thus, when saturated solution of nitrate is cooled the excess of it separates from solution, in the form of crystals.<\/p>\n
\nGive three factors which affect the solubility of a solid solute in a solvent.
\nSolution:
\n<\/span>The three factors on which the solubility of a solid depends are:<\/p>\n\n
\n(a) If you are given some copper sulphate crystals, how would you proceed to prepare its saturated solution at room temperature?
\n(b) How can you show that your solution is really saturated?
\nSolution:
\n<\/span>Take 100 g of distilled water in a beaker. To this add one gram of copper sulphate crystals.<\/p>\n
\n(a) Define (i) Henry’s law and (ii)\u00a0Crystallisation.
\n(b)State the different methods of\u00a0crystallisation.
\nSolution:
\n<\/span>(a) (i) Henry’s law:<\/strong> It states that at any given temperatures, the mass of a gas dissolved in a fixed volume of a liquid or solution is directly proportional to the pressure on the surface of a liquid.
\n(ii) Crystallisation:<\/strong> It is the process by which crystals of a substance separate out on cooling its hot saturated solution.<\/p>\n\n
\nWhat would you observe when crystals of copper (II) sulphate and iron (II) sulphate are separately heated in two test tubes?Solution:
\n<\/strong><\/span>Action of heat on copper (II) sulphate crystals
\n<\/strong>When copper (II) sulphate crystals are heated in a hard glass test tube, the following observations are made.
\n<\/p>\n\n
\n<\/li>\n<\/ol>\n\n
\n<\/li>\n<\/ol>\n
\nWhat is the effect of temperature on solubility of KNO3<\/sub>\u00a0and CaSO4<\/sub>\u00a0in water?
\nSolution:
\n<\/span>Potassium nitrate (KNO3<\/sub>): Increase in solubility of substances with rise in temperature.
\nCalcium\u00a0sulphate\u00a0(CaSO4<\/sub>): Decrease in solubility of substances with rise in temperature.<\/p>\n
\nSolubility of\u00a0NaCl\u00a0at 40o<\/sup>C is 36.5 g. What is meant by this statement?
\nSolution:
\n<\/span>Solubility of NaCl at 40\u00b0C is 36.5 g means 36.5 g of NaCl dissolves in 100 g of water at the temperature of 40\u00b0C.<\/p>\n
\nWhich test will you carry out to find out if a given solution is saturated or unsaturated or supersaturated?
\nSolution:<\/span><\/p>\n\n
\nWhat is the effect of pressure on solubility of gases? Explain with an example.
\nSolution:<\/span><\/p>\n\n
\nTo obtain this curve, values of temperature are plotted on X-axis and values of solubility on Y-axis.<\/p>\n\n
\nExplain why:<\/p>\n\n
\nNormally, solubility of crystalline solid increases with temperature. Does it increase uniformly in all cases? Name a substance whose solubility:
\n(a) Increases rapidly with temperature.
\n(b) Increases gradually with temperature.
\n(c) Increases slightly with temperature.
\n(d) Initially increases then decreases with rise in temperature.
\nSolution:
\n<\/span>(a) Potassium nitrate
\n(b) Potassium chloride
\n(c) Sodium chloride
\n(d) Calcium sulphate<\/p>\n
\nWhat are drying or desiccating agents? Give examples.
\nSolution:
\n<\/span>These are the substances which can readily absorb moisture from other substances without chemically reacting with them.
\nFor example,
\nPhosphorus\u00a0pentoxide\u00a0(P2<\/sub>O5<\/sub>), quick lime (CaO).<\/p>\n
\nComplete the following table:
\n
\nSolution:<\/span>
\n<\/p>\n
\nIn which of the following substances will there be
\n(a) Increase in mass
\n(b) Decrease in mass
\n(c) No change in mass when they are exposed to air?<\/p>\n\n
\n<\/span>(a) Increase in mass- Iron and conc. sulphuric acid
\n(b) Decrease in mass- Sodium carbonate crystals
\n(c) No change in mass- Sodium chloride<\/p>\n
\n(b) Solubility of solid decreases with fall in temperature. A saturated solution on cooling, a part of dissolved solute separates out in the form of crystals.<\/p>\n
\nNaCl\u00a0\u2192 36g
\nKCl\u00a0\u2192 35g
\nNH4<\/sub>Cl\u00a0\u2192 37 g<\/p>\n
\nWt. of dish and solution = 65 gm
\nWt. of dish and residue = 54.3 gm
\nWt. of saturated solution = 65 – 50 = 15 gm
\nWt. of crystals = 54.3 – 50 = 4.3 gm
\nWt. of water in saturated solution = 15 – 4.3 = 10.7 gm
\n<\/p>\n
\nSolubility at 500oC = 114 gm
\nSolubility at 30oC = 86 gm
\nSolubility from 50oC to 30oC = 114 – 86 = 28 gm.
\n
\n[Since, Wt. of water = Wt. of solution – Wt. of crystals]
\n50 g = Wt. of solution – Wt. of crystals
\n50 + 14 = Wt. of solution
\nWt. of solution = 64 gm
\nWt. of sodium = Wt. of saturated solution – Wt. of water
\n= 64 – 50 = 14 gm
\nWt. of sodium = 14 gm<\/p>\n
\nWhat do you understand by<\/p>\n\n
\n
\nWhat are the causes for<\/p>\n\n
\nThe presence of hydrogen carbonates of calcium and magnesium makes water temporarily hard.
\nThe presence of sulphates and chlorides of magnesium and calcium makes water permanently hard.<\/p>\n
\nWhat are the advantages of (i) soft water and (ii) hard water?
\nSolution:<\/span>
\nAdvantages of soft water:<\/strong>
\nWhen the water is soft, you use much less soap and fewer cleaning products. Your budget will reflect your savings.
\nPlumbing will last longer. Soft water is low in mineral content and therefore does not leave deposits in the pipes.
\nClothes last longer and remain bright longer if they are washed in soft water.
\nAdvantages of hard water:<\/strong>
\nWater free from dissolved salts has a very flat taste. The presence of salts in hard water makes it tasty. So, hard water is used in making beverages and wines.
\nCalcium and magnesium salts present in small amounts in hard water are essential for bone and teeth development.
\nHard water checks the poisoning of water by lead pipes. When these pipes are used for carrying water, some lead salts dissolve in water to make it poisonous. Calcium sulphate present in hard water forms insoluble lead sulphate in the form of a layer inside the lead pipe and this checks lead poisoning.<\/p>\n
\nWhat are\u00a0stalgmites\u00a0and stalactites? How are they formed?
\nSolution:<\/span>
\nIn some limestone caves, conical pillar-like objects hang from the roof and some rise from the floor. These are formed by water containing dissolved calcium hydrogen carbonate continuously dropping from the cracks in the rocks. Release of pressure results in the conversion of some hydrogen carbonate to calcium carbonate.
\nCa(HCO3<\/sub>)2<\/sub> \u2192 CaCO3<\/sub> + CO2<\/sub> + H2<\/sub>O
\nThis calcium carbonate little by little and slowly deposit on both roof and floor of the cave.
\nThe conical pillar which grows downwards from the roof is called stalactite and the one which grows upward from the floor of the cave is called stalagmite.
\nThese meet after a time. In a year, some grow less than even a centimetre, but some may be as tall as 100 cm.
\nCaCO3<\/sub> + CO2<\/sub> + H2<\/sub>O \u2192 Ca(HCO3<\/sub>)2<\/sub>
\nMgCO3<\/sub> + CO2<\/sub> + H2<\/sub>O \u2192 Mg(HCO3<\/sub>)2<\/sub>
\nIf the water flows over beds of gypsum (CaSO4<\/sub>.2H2<\/sub>O), a little bit of gypsum gets dissolved in water and makes it hard.<\/p>\n
\nName the substance which makes water (i) temporarily hard and (ii) permanently hard.
\nSolution:<\/span>
\nHydrogen carbonates of calcium and magnesium
\nSulphates and chlorides of magnesium and calcium<\/p>\n
\nGive equations to show what happens when temporary hard water is<\/p>\n\n
\n<\/p>\n
\nState the disadvantages of using hard water.
\nSolution:<\/span>
\nIt is more difficult to form lather with soap.
\nScum may form in a reaction with soap, wasting the soap.
\nCarbonates of calcium and magnesium form inside kettles. This wastes energy whenever you boil a kettle.
\nHot water pipes ‘fur up’. Carbonates of calcium and magnesium start to coat the inside of pipes which can eventually get blocked.<\/p>\n
\nWhat is soap? For what is it used?
\nSolution:<\/span>
\nSoap is chemically a sodium salt of stearic acid (an organic acid with the formula C17<\/sub>H35<\/sub>COOH) and has the formula C17<\/sub>H35<\/sub>COONa.
\nSoap is used for washing purposes.<\/p>\n