LAKHMIR SINGH AND MANJIT KAUR Solutions for Class 10 Chemistry Chapter 1 - Chemical Reactions and Equations

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Chapter 1 - Chemical Reactions and Equations Exercise 18

Solution 1

Respiration is an exothermic process because energy is produced during this process.

Solution 2

A balanced chemical equation has equal number of atoms of different elements in the reactants and products.

Solution 3

When quicklime is added to water, it forms slaked lime along with evolution of heat. There will be a rise in temperature of the bucket.

Solution 4

Magnesium ribbon should be cleaned before burning in air to remove the protective layer of basic magnesium carbonate from its surface.

Solution 5

False.

Solution 6

Oxygen should be in molecular form, O2

2Mg + O2 2MgO

Solution 7

The symbol (aq) represents aqueous solution in a chemical equation.

Solution 8

Photosynthesis is an endothermic reaction because sunlight energy is absorbed by green plants during this process.

Solution 9

(a) Aqueous solution is indicated by the symbol 'aq'.

(b) An exothermic reaction is indicated by writing "+Heat" or "+Heat energy" or "+Energy" on the products side of an equation.

(c) An endothermic reaction is indicated by writing "+Heat" or "+Heat energy" or "+Energy" on the reactants side of an equation.

Solution 10

(a) 2H2S + 3O2 2H2O + 2SO2

(b) P4 + 5O2 2P2O5

(c) CS2 + 3O2 CO2 + 2SO2

(d) 2Al + Fe2O3 Al2O3 + 2Fe

(e) BaCl2 + ZnSO4 ZnCl2 + BaSO4

Solution 11

(a) Ca(OH)2 + CO2 CaCO3 + H2O

(b) 2Al + 3CuCl2 2AlCl3 + 3Cu

Chapter 1 - Chemical Reactions and Equations Exercise 19

Solution 12

(a) 2NaOH + H2SO4 Na2SO4 + 2H2O

(b) Ca(OH)2 + CO2 CaCO3 + H2O

Solution 13

(i) Ca + 2H2O Ca(OH)2 + H2

(ii) N2 + 3H2 2NH3

Solution 14

(a) Ca (s) + 2H2O (l) Ca(OH)2 (aq) + H2 (g)

(b) 2SO2 (g) + O2 (g) 2SO3 (g)

Solution 15

(i) 4Na + O2 2Na2O

(ii) 2H2O2 2H2O + O2

(iii) Mg(OH)2 + 2HCl MgCl2 + 2H2O.

(iv) 4Fe + 3O2 2Fe2O3

(v) 2Al(OH)3 Al2O3 + 3H2O

(vi) 2NH3 + 3CuO 3Cu + N2 + 3H2O

(vii) Al2(SO4)3 + 6NaOH 2Al(OH)3 + 3Na2SO4

(viii) 2HNO3 + Ca(OH)2 Ca(NO3)2 + 2H2O

(ix) 2NaOH + H2SO4 Na2SO4 + 2H2O

(x) BaCl2 + H2SO4 BaSO4 + 2HCl

Solution 16

(a) Conservation of mass

(b) Aqueous; (aq)

Solution 17

(a) Magnesium Ribbon is heated in the presence of air to form a white powder called magnesium oxide.

(b) When dilute sulphuric acid is poured over zinc granules (i) there will be a rise in temperature (ii) evolution of hydrogen gas.

(c) (i) A yellow precipitate is formed.

     (ii) There will be a change in color (from colourless to yellow).

Solution 18

(a) The method of representing a chemical reaction with the help of symbols and formulae of substances involved in it is called a chemical equation.

Example: Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. This equation is written as: Zn + H2SO4ZnSO4 + H2

(b) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products.

Example: Zn + H2SO4ZnSO4 + H2

An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. It has unequal masses of various elements in the reactants and products.

Example: H2 + O2H2O

(c) (i) 2NH3 N2 + 3H2 (ii) C + CO2 2CO

Solution 19

H2 + CuO Cu + H2O

(i) Elements : H2 and Cu

(ii) Compounds : CuO and H2O

(iii) Reactants: H2 and CuO

(iv) Products: Cu and H2O

(v) Metal: Cu

(vi) Non-metal: H2

Solution 20

(a) The various ways in which a chemical equation can be made more informative are :

(i) By indicating the physical states of the reactants and products. Example: Gaseous state is indicated by the symbol (g).

Zn (s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g)

(ii) By indicating the heat changes taking place in the reaction. For xxample: An exothermic reaction is indicated by writing "+Heat" or "+Heat energy" or "+Energy" on the products side of an equation.

C (s) + O2 (g) CO2 (g) + Heat

(iii) By indicating the "conditions" under which the reaction takes place.

Example: Delta stands for heat which is written over the arrow of the equation.

(b) Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O (l)

Solution 21

(a) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products. A chemical equation should be balanced to satisfy the law of conservation of chemical reactions.

(b) 2Al + 3Cl2 2AlCl3

(c) 2K + 2H2O 2KOH + H2

Chapter 1 - Chemical Reactions and Equations Exercise 20

Solution 22

(a) The physical states of the reactants and products are shown by putting the "state symbols" in an equation.

For example: Zn (s) + H2SO4 (aq)ZnSO4 (aq) + H2 (g)

(b) Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)

(c) FeSO4(aq) + 2NaOH (aq) Fe(OH)2 (s) + Na2SO4 (aq)

Solution 23

(i) Evolution of gas.

For example: When sodium carbonate reacts with dilute hydrochloric acid, carbon dioxide gas is evolved.

(ii) Formation of a precipitate.

For example: When potassium iodide solution is added to a solution of lead nitrate, yellow precipitate of lead iodide is formed.

Solution 24

(a) 2Al(OH)3 + 3H2SO4 Al2(SO4)3 + 6H2O

(b) MnO2 + 4HCl MnCl2 + Cl2 + 2H2O

Solution 25

(a) MgCO3 (s) + 2HCl (aq) MgCl2 (aq) + CO2 (g) + H2O (l)

(b) 2NaOH (aq) + H2SO4 (aq) Na2SO4 (aq) + 2H2O (l)

Solution 26

The conditions for this reaction to take place are: a pressure of 300 atmospheres (written as 300 atm), a temperature of 300oC, and a catalyst which is a mixture of zinc oxide and chromium oxide (ZnO + CrO3).

Solution 27

(a) 2KClO3 (s) 2KCl (s) + 3O2 (g)

(b) 2Mg + CO2 2MgO + C

Solution 28

(a) CaCO3 + 2HCl CaCl2 + H2O + CO2

(b) NaOH (aq) + HCl (aq) NaCl (aq) + H2O (l)

Solution 29

4NH3 (g) + 3O2 (g) 2N2 (g) + 6H2O (l)

Solution 30

6CO2 (g) + 6H2O (l) C6H12O6 (aq) + 6O2 (g)

Carbon dioxide Water Glucose Oxygen

Solution 31

3BaCl2 (aq) + Al2(SO4)3 (aq) 3BaSO4 (s) + 2AlCl3 (aq)

Solution 32

2KNO3 (s) 2KNO2 (s) + O2 (g)

Solution 33

(a) Chemical reactions are the processes in which new substances with new properties are formed.

For example: When magnesium ribbon is heated, it burns in air to form a white powder called magnesium oxide.

(b) (i) The chemical reaction between zinc and dilute sulphuric acid.

(ii) The chemical reaction between citric acid and purple coloured potassium permanganate solution is characterised by change in colour (from purple to colourless).

(iii) The chemical reaction between potassium iodide and lead nitrate is characterised by the formation of a yellow precipitate of lead iodide.

(iv) The reaction between quick lime and water to form slaked lime is characterised by a change in temperature.

(v) When wax is burned, then water and carbon dioxide are formed. Wax is a solid; water is a liquid whereas carbon dioxide is a gas.

Chapter 1 - Chemical Reactions and Equations Exercise 21

Solution 34

(a) The various characteristics of chemical reactions are:

(i) Evolution of a gas (ii) Formation of a precipitate (iii) Change in colour (iv) Change in temperature (v) Change in state.

(b) (i) Evolution of carbon dioxide gas (ii) Change in colour from purple to colourless (iii) Formation of white precipitate of barium sulphate (iv) Change in temperature (v) Change in state from solid to liquid and gas.

Solution 35

(a) Those reactions in which heat is evolved are known as exothermic reactions.

 The reactions in which heat is absorbed are known as endothermic reactions.

(b) Example of exothermic reaction:

C (s) + O2 (g) CO2 + Heat

Example of endothermic reaction:

N2 (g) + O2 (g) + Heat 2NO (g)

(c) Endothermic reactions: Photosynthesis, Electrolysis of water, Decomposition of calcium carbonate.

Exothermic reactions: Burning of natural gas, Respiration.

Chapter 1 - Chemical Reactions and Equations Exercise 22

Solution 46

(a) Lead nitrate.

(b) Lead iodide.

(c) Formation of a precipitate.

(d) Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)

Solution 47

(a) Calcium oxide, CaO.

(b) Calcium hydroxide, Ca(OH)2

(c) Lime water.

(d) CaO + H2O Ca(OH)2

(e) Change in temperature.

Solution 48

(a) Zinc and Iron.

(b) Dilute hydrochloric acid and dilute sulphuric acid.

(c) Hydrogen.

(d) Lighter than air.

(e) Exothermic.

(f) Suppose metal X is zinc (Zn) and acid Y is dilute hydrochloric acid (HCl) ;

Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)

Solution 49

(a) Calcium carbonate (limestone), CaCO3

(b) Calcium oxide, CaO

(c) Carbon dioxide, CO2

(d) Calcium hydroxide, Ca(OH)2; Lime water.

(e) Calcium carbonate; Limestone and Marble.

Chapter 1 - Chemical Reactions and Equations Exercise 23

Solution 50

(a) Magnesium, Mg.

(b) Magnesium oxide, MgO

(c) Oxygen (of air), O2

(d) Magnesium hydroxide, Mg(OH)2; Used as antacid to relieve indigestion

(e) 2Mg + O2 2MgO

Solution 51

(a) Copper, Cu.

(b) Copper sulphate, CuSO4, Blue colour.

(c) Copper hydroxide, Cu(OH)2

(d) CuSO4 (aq) + 2NaOH (aq) Cu(OH)2 (s) + Na2S04 (aq)

Solution 52

(a) Sodium, Na.

(b) Sodium hydroxide solution (NaOH solution), Alkaline. (c) Hydrogen, H2

(d) 2Na + 2H2O 2NaOH + H2

(e) Exothermic.

Solution 53

(a) X is carbon monoxide gas (CO); Y is hydrogen gas (H2) ; Z is methanol (or Methyl alcohol) (CH3OH)

  (CH40 = CH3OH)

(b) Formation of Z:

 

The conditions for this reaction to take place are: a pressure of 300 atmospheres (written as 300 atm), a temperature of 300oC, and a catalyst which is a mixture of zinc oxide and chromium oxide (ZnO + CrO3).

Solution 54

(a) Potassium chlorate, KClO3

(b) Potassium chloride, KCl

(c) Oxygen, O2

(d) Manganese dioxide, MnO2; It acts as a catalyst in the decomposition of potassium chlorate to form oxygen gas

 (e) Catalysts

Solution 55

(a) Carbon dioxide, CO2

(b) Water, H2O

(c) Sunlight.

(d) Chlorophyll; Green leaves of plants.

(e) Glucose, C6H12O6

(f) Oxygen; Photosynthesis.

Chapter 1 - Chemical Reactions and Equations Exercise 45

Solution 1

Decomposition reaction.

Solution 2

The various types of chemical reactions are:

(i) Combination reactions.

(ii) Decomposition reaction.

(iii) Displacement reaction.

(iv) Double displacement reaction.

(v) Oxidation and reduction reactions.

Solution 3

The colour of copper sulphate solution changes when iron nail is kept immersed in it due to the displacement reaction taking place between iron and copper leading to formation of iron sulphate.

Solution 4

Zn + 2AgNO3  Zn(NO3)2 + 2Ag

Solution 5

Rancidity.

Solution 6

Anti-oxidants.

Solution 7

The digestion of food in the body is an example of decomposition reaction.

Solution 8

Anti-oxidant is a substance which prevents oxidation. They are added to fat and oil containing foods so that they do not get oxidized easily and hence do not turn rancid.

Solution 9

Food products containing fats and oils are packaged in nitrogen so that there is no oxygen to cause oxidation of food and make it rancid.

Solution 10

(a) When fused sodium chloride is decomposed by passing electricity, sodium metal is obtained.

(b) When lead nitrate is heated strongly, it breaks down to form lead monoxide, nitrogen dioxide and oxygen.

Solution 11

Decomposition reactions (carried out by electricity).

Solution 12

BHA (Butylated Hydroxy Anisole) and BHT (Butylated Hydroxy Toluene).

Solution 13

(a) Decomposition reaction where heat is supplied for energy:

(b) Decomposition reaction where light is supplied for energy:

 

(c) Decomposition reaction where electricity is supplied for energy:

Solution 14

2AgNO3 (aq) + Cu (s) Cu(NO3)2 (aq) + 2Ag (s)

Solution 15

(i) Decomposition.

(ii) Combination.

(iii) Decomposition.

(iv) Decomposition.

(v) Combination.

Chapter 1 - Chemical Reactions and Equations Exercise 46

Solution 16

(a) Combination.

(b) Decomposition.

(c) Decomposition.

(d) Decomposition.

(e) Combination.

Solution 17

(i) Displacement reaction.

(ii) Combination reaction.

(iii) Decomposition reaction.

(iv) Double displacement reaction.

(v) Displacement reaction.

Solution 18


Solution 19

(a) Displacement reaction.

(b) Combination reaction.

Solution 20

(a) Combination reaction.

(b) Displacement reaction.

(c) Displacement reaction.

(d) Decomposition reaction.

(e) Double displacement reaction.

Solution 21

(a) H2O2

(b) PbS

Solution 22

H2S

Solution 23

Substance oxidised: H2S

Substance reduced: SO2

Solution 24

(a) Oxidation; reduction.

(b) Reduction; oxidation.

(c) Rancidity.

Solution 25

Oxidation Reaction: The addition of oxygen (or removal of hydrogen) to a substance is called oxidation.

(i) C (ii) ZnO

Solution 26

(a) The oxidation and reduction reactions occurring together are called a redox reaction. Example:

       

In this reaction, copper oxide is being reduced to copper whereas hydrogen is being oxidised to water.

(b) Magnesium is oxidised as addition of oxygen to magnesium takes place leading to formation of magnesium oxide.

(c) (i) HCl

     (ii) MnO2

     (iii) MnO2

     (iv) HCl

Chapter 1 - Chemical Reactions and Equations Exercise 47

Solution 27

(a) Those reactions in which two or more substances combine to form a single substance is called a combination reaction.

(b) C (s) + O2 (g) CO2 + Heat

(c) N2 (g) + O2 (g) + Heat 2NO (g)

Solution 28

(a) C (s) + O2 (g) CO2 + Heat

(b) Oxidation reaction is an exothermic reaction.

(c)

In this reaction, copper oxide is being reduced to copper whereas hydrogen is being oxidised to water.

Solution 29

(a) The colour of ferrous sulphate is green. It changes to brown after heating.

(b) The product formed is ferric oxide. This is a decomposition reaction.

Solution 30

Those reactions in which a compound splits up into two or more simpler substances is called a decomposition reaction.

When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

Activity: When potassium chlorrate is heated in the presence of manganese dioxide catalyst, it decomposes to give potassium chloride and oxygen:

This decomposition takes place in the presence of heat and catalyst. In this decomposition reaction, a single compound, potassium chlorate, is splitting up into two simpler substances, potassium chloride and oxygen. This decomposition reaction is used for preparing oxygen gas in the laboratory.

Solution 31

ZnO + C Zn + CO

(i) Zinc oxide.

(ii) Carbon.

Solution 32

(a) 

(b)

Solution 33

(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.

Equation: CuSO4 (aq) + Zn (s) ZnSO4 + Cu

Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

Equation: AgNO3 (aq) + NaCl (aq) AgCl (s)+ NaNO3 (aq)

(b) Any reaction in which an insoluble solid (called precipitate) is formed that separates from the solution is called a precipitation reaction.

Example: The reaction between barium chloride and sodium sulphate solution to form a white barium sulphate precipitate (alongwith sodium chloride solution) is an example of a precipitation reaction.

 

Solution 35

(a) (i) H2S + Cl2 S + 2HCl

In this reaction, H2S is changing into S. That is, Hydrogen is being removed from hydrogen sulphide. Now, by definition, the removal of hydrogen from a compound is called oxidation, so, we can say that hydrogen sulphide is being oxidised to sulphur. On the other hand, Cl2 is changing into HCl. That is, hydrogen is being added to chlorine. By definition, the addition of hydrogen to a substance is called reduction, so we can say that chlorine is being reduced to hydrogen chloride.

(b) 2Mg + O2 2MgO

(i) Mg (ii) O2

Solution 36

(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.

Example: CuSO4 (aq) + Zn (s) ZnSO4 + Cu

When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained. In this reaction, zinc displaces copper from copper sulphate compound so that copper is set free. The blue colour of copper sulphate solution fades due to the formation of zinc sulphate.

(b) Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

Example: AgNO3 (aq) + NaCl (aq) AgCl (s)+ NaNO3 (aq)

When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed alongwith sodium nitrate solution. In this reaction, two compounds, silver nitrate and sodium chloride, react to form two new compounds, silver chloride and sodium nitrate.

Solution 37

Those reactions in which a compound splits up into two or more simpler substances are known as decomposition reactions.

Example: When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

 

They are called opposite of combination reactions because in a combination reaction, two or more substances combine to form a single substance.

Example: Magnesium and oxygen combine, when heated, to form magnesium oxide.

 

(b) Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s)

Solution 38

(a) When a piece of iron metal is placed in copper sulphate solution, then magnesium sulphate solution and copper metal are formed. This is a type of displacement reaction.

     

(b)

 

Solution 39

(a) H2

(b) CuO

(c) CuO

(d) H2

Solution 40

When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed alongwith sodium nitrate solution.

(a) AgNO3 (aq) + NaCl (aq) AgCl (s)+ NaNO3 (aq)

(b) Double displacement reaction.

Solution 41

When silver chloride is exposed to light, it decomposes to form silver metal and chlorine gas.

 

This reaction is used in black and white photography.

Solution 42

When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained.

(b) Displacement reaction.

Chapter 1 - Chemical Reactions and Equations Exercise 48

Solution 43

(a) Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a chemical (such as an acid) on their surface. Rusting of iron metal is the most common form of corrosion.

During the corrosion of iron, iron metal is oxidised by the oxygen of air in the presence of water (moisture) to form hydrated iron oxide called rust.

(b) Rusting.

(c) Oxidation.

(d) Railings, car bodies and bridges.

Solution 44

(a) The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called rancidity. It spoils the food materials prepared in fats and oils which have been kept for a considerable time and makes them unfit for eating.

(b) Oxidation.

(c) (i) Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils.

(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.

(iii) Rancidity can be retarded by keeping food in a refrigerator.

(iv) Rancidity can be prevented by storing food in air-tight containers.

(v) Storing foods away from light can also prevent rancidity.

Solution 45

(a) When barium chloride solution is added to sodium sulphate solution, then a white precipitate of barium sulphate is formed alongwith sodium chloride solution.

(b)

(c) Solid sodium sulphate and Solid barium chloride

(d) Double displacement reaction.

(e) Double displacement reaction between silver nitrate solution and sodium chloride solution forms a white precipitate of silver chloride and sodium nitrate solution.

Chapter 1 - Chemical Reactions and Equations Exercise 49

Solution 58

(a) Ferrous sulphate.

(b) Decomposition reaction.

(c)

Solution 59

(a) Lead nitrate.

(b) Nitrogen dioxide.

(c)

Solution 60

(a) Combination reaction.

(b) Decomposition reaction.

Solution 61

(a) Zinc (Zn)

(b) Copper (Cu)

(c) Copper sulphate (CuSO4)

(d) Displacement reaction;

CuSO4 (aq) + Zn (s) ZnSO4 (aq) + Cu (s)

(e) Brass

Solution 62

(a) Copper (Cu)

(b) Hydrogen (H2)

(c) Copper oxide (CuO)

(d) Water (H2O)

(e) CuO + H2 Cu + H2O

(f) Displacement reaction (which is also a redox reaction).

Solution 63

(a) Silver (Ag)

(b) Silver nitrate (AgNO3)

(c) Silver chloride (AgCl)

(d) AgNO3(aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)

(e) Double displacement reaction.

Chapter 1 - Chemical Reactions and Equations Exercise 50

Solution 64

(a) Metal X : Copper; Metal Y : Sodium

(b) Copper sulphate, CuSO4

(c) Sodium sulphate, Na2SO4

(d) Barium sulphate, BaSO4

(e) Copper chloride, CuCl2

Solution 65

(a) Copper sulphate.

(b) Blue colour.

(c) Copper sulphide.

(d) CuSO4 (aq) + H2S (g) CuS (s) + H2SO4 (aq)

(e) Double displacement reaction.

Solution 66

(a) Copper.

(b) Silver nitrate.

(c) Silver.

(d) Copper nitrate.

(e) Displacement reaction.

Solution 67

(a) Silver.

(b) Chlorine.

(c) Silver chloride.

(d) Silver nitrate and Sodium chloride.

(e) Decomposition reaction;