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Class 10 LAKHMIR SINGH AND MANJIT KAUR Solutions Chemistry Chapter 2 - Acids, Bases and Salts

Acids, Bases and Salts Exercise 66

Solution 1

(a) Yellow.

(b) Blue.

(c) Green.

Solution 2

(a) Red.

(b) Red.

Solution 3

Litmus.

Solution 4

Phenolphthalein.

Solution 5

Base.

Solution 6

Base.

Solution 7

When Hydrochloric acid reacts with an active metal (like zinc), we observe that gas filled bubbles are formed on the surface of the metal. Pass the gas formed through soap solution. Then, bring a burning candle near the gas filled soap bubble. If the gas present in bubble burns with a 'pop' sound, then its hydrogen gas.

Solution 8

Carbon dioxide (CO2) gas is evolved during the reaction. We pass this gas through lime water which turns milky because of the CO2 passing through it. If we keep on passing the gas through the milky lime water, it would become clear again.

Solution 9

Hydrochloric acid (HCl) and Sulphuric acid (H2SO4) are strong acids.

Acetic acid (CH3COOH) and Citric acid (C6H8O7) are weak acids.

Solution 10

(a) Citric acid - Lemon.

(b) Oxalic acid - Tomatoes.

(c) Lactic acid - Sour milk or curd.

(d) Tartaric acid - Tamarind.

Solution 11

Ant sting and Nettle leaf sting.

Solution 12

On diluting an acid, the concentration of hydronium ions (H3O+) in it decreases.

Solution 13

Acids, Bases and Salts Exercise 67

Solution 14

Solution 15

(a) Sour; blue; bed.

(b) Water.

(c) Hydrogen.

(d) Olfactory.

(e) Olfactory.

Solution 16

(a) An indicator is a 'dye' that changes colour when it is put in an acid or a base. The three most common indicators are: Litmus, Methyl orange and Phenolphthalein.

(b) Litmus.

(c) Red.

Solution 17

Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators. Onion and vanilla extracts are olfactory indicators. When a basic solution like sodium hydroxide solution is added to a cloth strip treated with onions (or onion extract), then the onion smell cannot be detected.

Solution 18

(a) When an acid reacts with a metal, then a salt and hydrogen gas are formed.

(b) Hydrogen gas is liberated when an acid reacts with a metal. When reaction between an acid and a metal occurs, we observe formation of gas bubbles. When these gas bubbles are passed through soap solution, gas filled soap bubbles rise into the air. When a burning candle is brought near a gas-filled soap bubble, the gas present in the soap-bubble burns with a 'pop' sound. Only hydrogen gas burns making a 'pop' sound. This shows that hydrogen gas is evolved in the process.

Solution 19

When a concentrated acid is added to water for preparing a dilute acid, then the heat is evolved gradually and easily absorbed by the large amount of water (to which the acid is being added) however if water is added to concentrated acid, then large amount of heat is evolved at once. This heat changes some of the water to steam explosively which can splash the acid on our face or clothes and cause acid burns. Even the glass container may break due to the excessive heating.

Solution 20

When an acid reacts with a metal hydrogen carbonate, then a salt, carbon dioxide gas and water are formed.


Solution 21

(a) When dilute hydrochloric acid reacts with sodium carbonate, then sodium chloride, carbon dioxide and water are formed.

(b) CO2 gas is liberated during the reaction.

When carbon dioxide gas formed in the form of brisk effervescence is passed through lime water, it turns the lime water milky. If excess of carbon dioxide gas is passed through the milky lime water, the solution becomes clear again. This confirms the presence of carbon dioxide gas.

Solution 22

When an acid reacts with a base, then a salt and water are formed. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.

Such a reaction is termed as neutralisation reaction.

Solution 23

Acids react with metal oxides to form salt and water.

For example: Copper (II) Oxide, a metal oxide reacts with dilute hydrochloric acid to form copper chloride and water

Solution 24

(a) Organic acids are acids present in plant materials and animals. These are naturally occuring acids.

     A mineral acid (or inorganic acid) is an acid derived from one or more minerals of the earth.

(b) Organic acids: Citric acid, lactic acid;

      Mineral acids: Hydrochloric acid, sulphuric acid.

(c) Uses of mineral acids in industry:

(i) Sulphuric acid is used in the manufacture of fertilizers, paints, dyes, detergents etc.

(ii) Nitric acid is used for making fertilizers, explosives, dyes and plastics.

(iii) Hydrochloric acid is used for removing oxide film from steel objects, in textile, food and leather industries.

Solution 25

A strong acid is one that completely ionises in water to form a large amount of hydrogen ions whereas a weak acid only partially ionises in water and thus produces a small amount of hydrogen ions.

HCl, H2SO4, HNO3 are strong acids; CH3COOH, H2CO3, H2SO3 are weak acids.

Solution 26

The acidic character of a substance is due to the presence of hydrogen ions [H+(aq) ions] in its aqueous solution. HCl, H2SO4 etc show acidic properties because they produce hydrogen ions when dissolved in water. The solution of compounds like alcohol and glucose do not show acidic character because they do not ionize in water to produce hydrogen ions or any other ions in solution.

Solution 27

The reaction between an acid and a base to form salt and water is called a neutralisation reaction. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.

Solution 28

Curd and other sour substances contains acids which can react with the metals of brass and copper vessels to form toxic (poisonous) metal compounds which can cause food poisoning and damage our health.

Solution 29

(a) Salt and water.

(b) Because dry HCl gas has no hydrogen ions (H+ ions) in it which can impart acidic properties to it.

(c) Pink.

Solution 30

(a) The acidic behavior of an acid is due to the presence of hydrogen ions [H+ (aq) ions] which are produced only when acids are dissolved in water. In the absence of water, acids do not produce hydrogen ions and hence do not show acidic behavior.

(b) The aqueous solution of an acid conducts electricity due to the presence of charged particles called 'ions' in it. These ions carry electric current.

(c) Distilled water does not conduct electricity because it does not contain any ionic compounds dissolved in it whereas rain water does.

Reason: When rain water falls on earth through the atmosphere, it dissolves an acidic gas 'carbon dioxide' from the air and forms carbonic acid (H2CO3). The carbonic acid provides some hydrogen and carbonate ions to the rain water. Due to the presence of these ions, rain water conducts electricity.

Acids, Bases and Salts Exercise 68

Solution 31

(a) When an acid reacts with a metal carbonate, then a salt, carbon dioxide and water are produced.

Example: When dilute hydrochloric acid reacts with sodium carbonate, then sodium chloride, carbon dioxide and water are formed.

 

(b) (i) Lime water turns milky.


(ii) Lime water solution becomes clear.

 

Solution 32

Activity:

Take about 1g solid NaCl in a clean and dry test tube and add some concentrated sulphuric acid to it. Fit a rubber cork with a small delivery tube in the mouth of the test tube. Concentrated sulphuric acid reacts with sodium chloride to form hydrogen chloride gas. The hydrogen chloride gas starts coming out of the open end of the glass tube.

 

Now, hold a 'dry' blue litmus paper in HCl gas. There is no change in colour of the 'dry' blue litmus paper. This shows that HCl gas does not behave as an acid in the absence of water. However, when we hold a 'moist' blue litmus paper in HCl gas, we will see that the 'moist' blue litmus paper turns red. This indicates that HCl gas shows acidic behavior in the presence of water as hydrogen ions are formed. This proves that acids produce ions only in aqueous solutions or in presence of water.

Solution 33

(a) Hydrogen.

(b) Activity:

Take solutions of glucose, alcohol, hydrochloric acid and sulphuric acid. Fix two nails on a cork, and place the cork in a 100 ml beaker. Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch. Now pour some dilute HCl in the beaker and switch on the current. The bulb starts glowing. This shows that HCl solution taken in the beaker conducts electricity. If we replace hydrochloric acid with sulphuric acid and perform the experiment, the bulb would glow again. This shows that an aqueous solution of an acid conducts electricity due to the presence of charged particles called ions in it.

Now, if we take glucose solution in the beaker and switch on the current, the bulb would not glow. If we repeat the experiment by taking alcohol solution in the beaker, the bulb would not glow again. This shows that due to the absence of ions, glucose and alcohol solutions do not conduct electricity. From this activity, we conclude that the hydrogen containing compounds such as glucose and alcohol are not categorised as acids because they do not dissociate (or ionise) in water to produce hydrogen ions [H+(aq) ions].

Solution 44

(a) X is carbon dioxide; Y is calcium carbonate; Z is calcium hydrogen carbonate.

(b) (i)

     (ii)

     (iii)

Solution 45

Baking soda solution. Being basic in nature, it neutralises excess acid in the stomach.

Acids, Bases and Salts Exercise 69

Solution 46

(a) Copper (II) chloride, CuCl2

(b)

(c) Copper oxide is basic in nature

Solution 47

(a) Turmeric.

(b) The yellow stain of curry turns reddish-brown when soap is scrubbed on it because of the fact that soap solution is basic in nature which changes the colour of turmeric in the curry stain to red-brown. This stain turns yellow again when the cloth is rinsed with water because then the basic soap gets removed with water.

(c) Basic.

Solution 48

Acidic solution will turn blue litmus red; This red litmus will turn blue in basic solution; Distilled water will have no effect on any type of litmus paper.

Solution 49

Substance X is sodium hydrogen carbonate; Gas Y is carbon dioxide.

Solution 50

Neutralisation of a carbonate with an acid produces carbon dioxide gas but not with an oxide or hydroxide.

Solution 51

(a) H+ ions of acid combine with OH- ions of alkali to form water, H2O.

(b) Temperature of the solution rises.

Acids, Bases and Salts Exercise 79

Solution 1

(a) Hydrogen

(b) Hydrogen

Solution 2

Alkalis

Solution 3

They all produce hydroxide ions when dissolved in water.

Solution 4

Tooth decay start when the pH of mouth is lower than 5.5 because the acid becomes strong enough to attack the enamel of the teeth and corrode it.

Solution 5

7

Solution 6

Solution of pH = 2 is more acidic.

Solution 7

Solution of pH = 11

Solution 8

Sorenson

Solution 9

Universal indicator

Solution 10

Soil B.

Soil B is acidic in nature so its treated with powdered chalk to reduce its acidity.

Solution 11

Universal indicator

Solution 12

(a) Dark Purple

(b) Orange Yellow

(c) Red

Solution 13

pH = 1 will turn the scale red; strong acid.

Solution 14

Solution Y is a stronger acid.

Solution 15

Solution A (pH = 3.0) will turn litmus from solution blue to red

Solution B (pH = 9.5) will turn phenolphthalein from colourless to pink.

Solution 16

Drink Q has a pH value of 9.

Solution 17

Alkaline reaction: Solution Y (pH = 8)

Acidic reaction: Solution X (pH = 4)

Solution 18

(a) Lower.

(b) Higher.

(c) 7.

(d) Lower.

(e) Higher.

Solution 19

pH value will decrease when milk changes to curd. Curd contains lactic acid hence the pH decreases.

Solution 20

(a) Universal indicator is a mixture of many different indicators which gives different colours at different pH values of the entire pH scale. It is used to obtain an idea of how acidic or basic a substance is.

(b) When an acid or base solution is added to the universal indicator, it produces a new colour which is used to find the pH value of the acid or the base solution by matching the colour with the colours on pH colour chart.

(c) Green colour.

Solution 21

(a) Methanoic acid.

(b) Methanoic acid.

The effect of methanoic acid can be neutralised by rubbing a mild base like baking soda solution on the stung area of the skin.

Acids, Bases and Salts Exercise 80

Solution 22

(a) Tooth decay starts when the pH of the acid formed in the mouth falls below 5.5 because the acid becomes strong enough to attack the enamel of the teeth and corrode it.

(b) The pH of lake water becomes lower because of too much acid rain. The high acidity of lake water can kill the aquatic animals like fish since they can survive within a narrow range of pH change.

Calcium carbonate is added to acidic lake water to neutralise the acid and this prevents the fish from being killed.

Solution 23

(a) When a bee stings a person, it injects an acidic liquid into the skin which causes immense pain and irritation. Its remedy is to rub a mild base like baking soda solution on the stung are of the skin.

(b) When a wasp stings, it injects an alkaline liquid into the skin. Rubbing a mild acid like vinegar on the stung area of the skin gives relief.

Solution 24

(a) Since vinegar is acetic acid so it can't be used to treat bee sting because bee injects acid into the skin.

(b) Since baking soda is basic in nature so it can't be used to treat wasp sting because wasp injects alkaline liquid into the skin.

Solution 25

(a) pH of a solution signifies the concentration of hydrogen ions in it.

Solution B is highly acidic since it has the lowest pH (pH = 4).

(b) Slaked lime or Chalk can be used to treat acidic soil.

Solution 26

(a) (i) Acids; A, C and D.

(ii) Alkalis; B, E and F.

(b) (i) Sulphuric acid.

(ii) Sulphuric acid.

(iii) Sodium hydroxide.

(iv) Nitric acid.

Solution 28

When the soil is too acidic, it is treated with bases like quicklime or slaked lime or chalk.

Solution 29

Our stomach produces hydrochloric acid. If there is excess of hydrochloric acid in the stomach, it causes indigestion which produces pain and irritation. Its effect can be cured by taking antacids.

Solution 30

If the soil is too acidic, then it can be treated with materials like quicklime or slaked lime as these materials are bases and hence react with the excess acids present in the soil to reduce its acidity.

Solution 31

Strong base: A base which completely ionises in water and produces a large amount of hydroxide ions.

Weak base: A base which is partially ionised in water and produces a small amount of hydroxide ions.

Strong bases: NaOH, KOH

Weak bases: NH4OH, Ca(OH)2, Mg(OH)2

Solution 32

(i) H+, Cl-

(ii) H+, NO32-

(iii) H+, SO42-

(iv) Na+, OH-

(v) K+, OH-

(vi) Mg2+, OH-

Solution 33

(a) pH of pure water = 7

(b) Aqueous solution of sugar will turn the color of universal indicator green because sugar solution is neutral in nature.

(c) pH of the sample of rain water will be between 5 and 6. It is a weak acid.

Solution 34

(a) The pH in the stomach of a person suffering from indigestion will be less than 7 since indigestion is caused due to formation of excess acid in the stomach.

(b) Antacids are a group of mild bases so they have pH more than 7.

(c) Antacids react with excess acid in the stomach and neutralise it.

(d) Antacids: Magnesium hydroxide and Sodium hydrogencarbonate.

Solution 35

Substances having pH values above 7: Solution of washing soda and toothpaste; They will turn red litmus paper blue due to their basic nature.

Substances having pH values less than 7: Lemon juice, vinegar and stomach juices; They will turn blue litmus paper red due to their acidic nature.

Solution 36

(a) Yes, all basic solutions have H+ ions. They are basic because the concentration of hydrogen ions is much less than that of hydroxide ions.

(b) When a solution becomes more acidic, pH gets lower.

Solution 37

(a) Acids are those chemical substances which have a sour taste. Example: Acetic acid and citric acid.

     Base is a chemical substance which has a bitter taste. Example: Caustic soda and washing soda.

(b) Strong bases - Sodium hydroxide, NaOH, potassium hydroxide (KOH).

     Weak bases - Calcium hydroxide, Ca(OH2), ammonium hydroxide, NH4OH.

(c) (i) Hydrogen ions.

    (ii) Hydroxide ions.

(d)


(e) Uses of bases:

(i) Sodium hydroxide is used in the manufacture of soap, paper and rayon.

(ii) Calcium hydroxide is used in the manufacture of bleaching powder.

Solution 27

(a) The cold drink turns blue litmus red because of its acidic nature. It will have no action on red litmus.

(b) A < C < B.

B will have maximum acid strength because pH is inversely proportional to concentration of hydrogen ions in a solution.

Acids, Bases and Salts Exercise 81

Solution 38

(a) When zinc granules are heated with sodium hydroxide solution, then sodium zincate salt and hydrogen gas are formed.

 

(b) When bases react with non-metal oxides, then salt and water are formed.

Example: Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water.

 

Solution 39

(a) As the concentration of hydrogen ions increases, the solution becomes more acidic.

(b) As the concentration of hydroxide ions increases, the solution becomes more basic.

(c) Vinegar is acidic in nature.

(d) Soap is basic in nature.

(e) (i) pH = 9 : Alkaline.

     (ii) pH = 4 : Acidic.

     (iii) pH = 7 : Neutral.

     (iv) pH = 1 : Acidic.

     (v) pH = 10 : Alkaline.

     (vi) pH = 3 : Acidic.

Acids, Bases and Salts Exercise 82

Solution 54

(a) Milk is made slightly alkaline so that it may not become sour easily due to the formation of lactic acid in it.

(b) The alkaline milk takes a longer time to set into curd because the lactic acid being formed has to first neutralise the alkali present in it.

Solution 55

Carbon and Sulphur being non-metals form acidic oxides.

Solution 56

(i) Weakly alkaline: D (pH = 11)

(ii) Neutral: C (pH = 7)

(iii) Strongly acidic: A (pH = 1)

(iv) Strongly alkaline: E (pH = 13)

(v) Weakly acidic: B (pH = 5)

Solution 57

(a) Potatoes grow better in acidic soil having pH = 5.5

(b) Broccoli grows better in alkaline soil since adding a lot of lime to acidic soil will make it basic in nature.

Solution 58

Sulphuric acid < car battery acid < washing up liquid < milk of magnesia < metal polish < oven cleaner since:

Red : pH = 1

Pink : pH = 3-4

Yellow: pH = 5-6

Light blue : pH = 9

 Dark blue : pH = 10

Purple: pH = 11


Solution 59

(a) Solution A turns universal indicator blue to purple so it is basic in nature and will turn litmus blue.

(b) Solution B turns universal indicator orange to red so it is acidic in nature and will turn litmus red.

(c) Milk of magnesia and sodium hydroxide solution are bases like solution A.

(d) Lemon juice and hydrochloric acid are acids like solution B.

(e) Neutralisation reaction.

Solution 60

(a) Wasp stings are alkaline in nature since they are treated using acids like vinegar.

(b) Bee stings are acidic in nature since they are treated using bases like baking soda.

Solution 61

(a) The pH in a person's mouth becomes lower after each meal because bacteria present in the mouth breaks down the sugar to form acids.

(b) If the pH is low, the tooth starts decaying.

(c) A person can lessen the chances of suffering from tooth decay by changing his eating habits such as eating less of sugary foods like ice-creams, candies, sweets etc.

Solution 62

(a) Universal indicator paper is used to measure the pH.

(b) Lemon juice with pH = 2.5 is the most acidic.

(c) Household ammonia with pH = 12 is the most alkaline.

(d) Salt solution and sugar solution with pH = 7 are neutral.

(e) Vinegar (acid) can be used to treat wasp stings since it injects an alkaline liquid into the skin.

(f) Baking soda can be used to treat bee stings since it injects methanoic acid into the skin.

Acids, Bases and Salts Exercise 83

Solution 63

(a) X is zinc metal; Gas Y is hydrogen gas.

(b) (i)


(ii)

 

Acids, Bases and Salts Exercise 96

Solution 1

(a) NaHCO3.

(b) Na2CO3.

Solution 2

(i) Na2CO3.

(ii) Na2CO3.10H2O.

Solution 3

False.

Solution 4

CuSO4.5H2O has blue colour due to the presence of water of crystallization.

Solution 5

Blue.

Solution 6

The common name is Gypsum and the chemical name is calcium sulphate dihydrate.

Solution 7

Calcium hydroxide.

Solution 8

Plaster of Paris.

Acids, Bases and Salts Exercise 97

Solution 9

Hydrochloric acid.

Solution 10

Plaster of Paris

Solution 11

Sodium carbonate.

Solution 12

Sodium carbonate.

Solution 13

Tartaric acid.

Solution 14

Sodium.

Solution 15

NaHCO3.

Solution 16

(a) Baking soda.

(b) Washing soda.

Solution 17

(a) Sodium chloride - NaCl.

(b) Sodium hydroxide - NaOH.

Solution 18

Common salt occurs naturally in sea water and as rock salt.

Solution 19

Sodium chloride.

Solution 20

Common salt is obtained from sea water by the process of evaporation.

Solution 21

Sodium chloride is required in our body for the working of nervous system, the movement of muscles, and the production of hydrochloric acid in the stomach.

Solution 22

Sodium hydroxide, sodium carbonate and sodium hydrogencarbonate.

Solution 23

(a) It is used in the manufacture of soap.

(b) It is used in cooking food.

Solution 24

Rock salt. It is mined from the underground deposits just like coal.

Solution 25

Sodium chloride.

Solution 26

Sodium chloride.

Solution 27

Sodium hydroxide, chlorine and hydrogen.

Solution 28

(a) Anode.

(b) Cathode.

(c) Near the cathode.

Solution 30


Solution 31

Washing soda is sodium carbonate decahydrate. Properties: (i) It is transparent crystalline solid.

(ii) It is soluble in water.

Uses: (i) It is used for removing permanent hardness of water.

(ii) It is used in the manufacture of glass, soap and paper.

Solution 32

Sodium chloride - NaCl.

Sodium carbonate - Na2CO3.

The aqueous solution of sodium chloride is neutral because it is formed from a strong acid and a strong base. The aqueous solution of sodium carbonate is basic because it gets hydrolysed to some extent and forms sodium hydroxide which is a strong base and carbonic acid which is a weak acid.

Solution 33

The chemical formula of ammonium chloride is NH4Cl. Since, ammonium chloride is the salt of a strong acid HCl and a weak base NH4OH, so an aqueous solution of ammonium chloride is acidic in nature.

When dissolved in water, it gets hydrolysed to some extent to form HCl and NH4OH. HCl being a strong acid is fully ionised and gives a large amount of hydrogen ions whereas NH4OH is only slightly ionised. So, NH4Cl contains more of hydrogen ions than hydroxide ions and is hence acidic in nature.

Solution 34

Baking soda is a substance added to food for its faster cooking. Its chemical name is sodium hydrogen carbonate.

Uses: (i) It is used as an antacid to remove acidity of stomach.

         (ii) It is used in fire extinguishers.

Baking soda is sodium hydrogencarbonate whereas washing soda is sodium carbonate decahydrate.

Solution 35

Sodium hydrogencarbonate is produced on large scale by reacting a cold and concentrated solution of sodium chloride with ammonia and carbon dioxide.

Solution 36

When a cold and concentrated solution of sodium chloride reacts with ammonia and carbon dioxide, sodium hydrogencarbonate and ammonium chloride are formed.

Exercise

Solution

Solution

Acids, Bases and Salts Exercise 98

Solution 37

(a) The water molecules which form part of the structure of a crystal are called water of crystallization.

Example: CuSO4.5H2O

(b) The blue copper sulphate crystals contain water of crystallization as it is blue in colour.

(c) Anhydrous copper sulphate turns blue on adding water. This property of anhydrous copper sulphate is used to detect the presence of moisture in a liquid.

Solution 38

(a) Baking soda.

(b) When a solution of sodium hydrogencarbonate is heated, then it decomposes to give sodium carbonate with the evolution of carbon dioxide gas.

(c) Sodium hydrogencarbonate is used as an antacid because it neutralises the excess acid present in the stomach and relieves indigestion.

Solution 39

(a) If heating is not controlled while preparing POP, then all the water of crystallisation of gypsum is eliminated and it turns into a dead burnt plaster.

(b)

Solution 40

(a) On strong heating, blue copper sulphate crystals turn white.

(b) When water is added to anhydrous copper sulphate, it gets hydrated and turns blue.

Solution 41

(a) Sodium hydrogencarbonate and tartaric acid.

(b) Baking powder is a mixture of baking soda and tartaric acid whereas baking soda is only sodium hydrogencarbonate.

(c) When baking powder mixes with water, then sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake soft and spongy.

Solution 42

(a) Calcium oxychloride.

(b) CaOCl2

(c) Calcium hydroxide and chlorine.

(d) It is used for disinfecting drinking water supply.

Solution 43

Working:

A soda-acid type fire extinguisher contains a solution of sodium hydrogencarbonate and sulphuric acid in separate containers in separate containers inside them. When the knob of the fire extinguisher is pressed, then sulphuric acid mixes with sodium hydrogencarbonate solution to produce carbon dioxide gas which forms a blanket around the burning substance and cuts off the supply of air to burning substance; this stops the process of burning and fire gets extinguished.

Solution 44

(a) Sodium carbonate.

(b) Bleaching powder.

(c) Sodium carbonate.

(d) Bleaching powder.

(e) It sets into a hard mass on mixing with proper quantity of water.

(f) Bleaching powder.

Solution 46

(a) Baking powder is a mixture of baking soda and tartaric acid. When baking powder mixes with water, then sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake soft and spongy.

(b) Substance X is tartaric acid. It can react with any sodium carbonate formed and neutralise it otherwise cakes and bread will taste bitter.

Solution 47

(a) Sodium hydroxide:

(i) It is used for making soaps and detergents.

(ii) It is used in the manufacture of paper.

(b) Chlorine:

(i) It is used in the production of bleaching powder.

(ii) It is used in the production of hydrochloric acid.

(c) Hydrogen:

(i) It is used in the production of hydrochloric acid.

(ii) It is used in the hydrogenation of oils.

(d) Hydrochloric acid:

(i) It is used in medicines and cosmetics.

(ii) It is used in textile/dyeing and tanning industries.

Solution 48

(a) Bleaching powder.

(b) Gypsum.

(c) It sets into a hard mass in about 30 mins.

(d) Chlorine is used for sterilising drinking water supply because it is a disinfectant which kills germs or bacteria.

Solution 49

(a) When a concentrated solution of sodium chloride is electrolysed, it decomposes to form sodium hydroxide, chlorine and hydrogen.

(b) Because of the products formed: Chlor for chlorine and alkali for sodium hydroxide.

(c) Sodium hydroxide, chlorine and hydrogen.

Uses of Sodium hydroxide:

(i) It is used for making soaps and detergents.

(ii) It is used in the manufacture of paper.

Uses of chlorine:

(i) It is used in the production of bleaching powder.

(ii) It is used in the production of hydrochloric acid.

Uses of hydrogen:

(i) It is used in the production of hydrochloric acid.

(ii) It is used in the hydrogenation of oils.

Solution 50

(a) Production of washing soda: Washing soda is produced from sodium chloride (or common salt) in the following three steps:

(i) A cold and concentrated solution of sodium chloride (called brine) is reacted with ammonia and carbon dioxide to obtain sodium hydrogencarbonate :

Sodium hydrogencarbonate formed is only slightly soluble in water, so it precipitates out as a solid.

(ii) Sodium hydrogencarbonate is separated by filtration, dried and heated. On heating, sodium hydrogencarbonate decomposes to form sodium carbonate:

The anhydrous sodium carbonate obtained here is called soda ash.

(iii) Anhydrous sodium carbonate (soda ash) is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystallisation :

(b) An aqueous solution of washing soda is alkaline because it turns red litmus to blue.

(c) Washing soda has detergent properties because it can remove dirt and grease from dirty clothes.

(d) (i) It is used as cleansing agent for domestic purposes.

(ii) It is used for removing permanent hardness of water.

Acids, Bases and Salts Exercise 99

Solution 51

(a) Bleaching powder is Calcium oxychloride (CaOCl2). It is prepared by passing chlorine gas over dry slaked lime.

(b) When bleaching powder reacts with dilute sulphuric acid , it produces chlorine gas.

(c) (i) It is used for disinfecting drinking water supply.

(ii) It is used in the manufacture of chloroform.

Solution 52

(a) Plaster of paris is calcium sulphate hemihydrate. Its chemical formula is: CaSO4.1/2H2O.

(b) It is prepared by heating gypsum to a temperature of 100oC in a kiln; it loses 3/4th of its water of crystallisation and forms plaster of paris.

(c) This is because the presence of moisture can cause the slow setting of plaster of Paris by bringing about its hydration.

(d) Uses of plaster of Paris:

(i) It is used as a fire proofing material.

(ii) it is used in hospitals for setting fractured bones in the right position to ensure correct healing.

Solution 53

(a) A salt is a compound formed from an acid by the replacement of the hydrogen in the acid by a metal.

Example: Sodium chloride - NaCl; It is obtained from hydrochloric acid and sodium metal.

Ammonium chloride - NH4Cl; It is obtained from ammonia and hydrochloric acid.

(b) The salts having the same positive ions are said to belong to a family of salts.

Example: Sodium chloride and sodium sulphate belong to the same family of salts called sodium salts.

(c) The salts which contain water of crystallisation are called hydrated salts.

Example: Copper sulphate crystals contain 5 molecules of water of crystallisation.

The salts which have lost their water of crystallisation are called anhydrous salts.

Example: On strong heating, copper sulphate crystals lose all the water of crystallisation and form anhydrous copper sulphate.

(d) Copper sulphate pentahydrate salt - Its chemical formula is CuSO4.5H2O. It is blue in colour.

Iron sulphate heptahydrate salt - Its chemical formula is FeSO4.7H2O. It is green in colour.

(e) The aqueous solution of ammonium chloride salt turns blue litmus red.

Acids, Bases and Salts Exercise 100

Solution 69

(a) No solution will turn blue litmus to red.

(b) Solution Q (sodium hydroxide) will turn red litmus blue.

Solution 70

A is copper sulphate pentahydrate, CuSO4.5H2O

B is water, H2O

C is anhydrous copper sulphate, CuSO4

D is water, H2O

Solution 71

X is Sodium chloride.

The process is called Chlor-alkali process.

Solution 72

(a) Ca(OH)2 and Cl2

(b) NaCl, NH3, H2O and CO2

(c) 2CaSO4.H2O

(d) NaHCO3

(e) NaHCO3

Solution 73

(a) Ammonium chloride, NH4Cl

(b) Sodium chloride, NaCl

(c) Sodium carbonate, Na2CO3

Solution 74

(a) Plaster of Paris.

(b)

(c) POP is used in hospitals for setting fractured bones in the right position to ensure correct healing.

Solution 75

Solution 76

Bleaching powder, CaOCl2.

Solution 77

Salt X is like sodium carbonate, Na2CO3, which is made from a strong base and a weak acid. On dissolving in water, salt X gets hydrolysed to form some strong base and some weak acid. The strong base thus formed makes the solution alkaline which turns red litmus blue.

Solution 78

Baking powder; When baking powder mixes with water, then sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake soft and spongy.

Solution 79

Plaster of Paris.

Solution 80

Sodium hypochlorite, NaClO; used in making household bleaches and for bleaching fabrics.

Solution 81

(a) Gypsum - CaSO4.2H2O

(b) Copper sulphate crystals - CuSO4.5H2O

(c) Sodium carbonate crystals - Na2CO3.10H2O

Solution 82

(a) 5.

(b) 10.

(c) 2.

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