Lakhmir Singh Chemistry Ch 1 Solution Class 10 Chemical Reactions and Equations
byMr. Chandan
S.Chand Solution for Class 10 Chemistry Ch 1 : Chemical Reactions and Equations
Lakhmir Singh Solutions for Class 10 Chemistry Chapter 1 Chemical Reactions and Equations deal with various chemical reactions, their examples and corresponding chemical equations. A chemical reaction is a process in which new substances with new properties are formed. It involves the rearrangement of atoms and the breaking of chemical bonds.
In a chemical reaction, mainly, there will be two sides, one is the reactant side, and the other one is the product side. Two reactants combine to form products, or reactants are transformed into products in a chemical reaction. The method of representing a chemical reaction with the help of symbols and formulae of the substance involved is known as chemical equations.
Very Short Answer Type Questions - Page no : 18 & 19
1. Why is respiration considered an exothermic process ?
Answer :
Respiration is considered an exothermic process because energy is produced during this process.
2. On what basis is a chemical equation balanced ?
Answer :
A balanced chemical euation has an equal number of atoms of different elements in reactants and products.
3. What happens chemically when quicklime is added to water filled in a bucket ?
Answer :
When quicklime is added to water, it forms slaked lime along with evolution of heat. There will be rise in temperature of bucket.
4. Why should magnesium ribbon be cleaned before burning in air ?
Answer :
Magnesium ribbon should be cleaned before burning in air to remove the protective layer of magnesium oxide from its surface.
5. State whether the following statement is true or false :
A chemical equation can be balanced easily by altering the formula of a reactant or product.
Answer :
False
6. What is wrong with the following chemical equation ?
Mg + O → MgO
Correct and balance it.
Answer :
The wrong with chemical equation is that the molecular formula of oxygen should be O2
Balanced equation : 2Mg + O2 → 2MgO
7. What does the symbol (aq) represent in a chemical equation ?
Answer :
The symbol (aq) represents aqueous solution in a chemical equation.
8. Why is photosynthesis considered an endothermic reaction ?
Answer :
Photosynthesis is considered an endothermic reaction because sunlight energy is absorbed during this process.
9. How will you indicate the following effects in a chemical equation ?
(a) A solution made in water
(b) Exothermic reaction
(c) Endothermic reaction
Answers :
(a) A solution made in water is known as aqueous solution and represented by 'aq'.
(b) An exothermic reaction is indicated by writing "+heat" or "+heat energy" or just "energy" on the products side of an equation.
(c) An endothermic reaction is indicated by writing "+heat" or "+heat energy" or just "energy" on the reactants side of an equation.
10. Translate the following statements into chemical equations and then balance the equations :
(a) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(b) Phosphorus burns in oxygen to give phosphorus pentoxide.
(c) Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide.
(d) Aluminium metal replaces iron from ferric oxide, Fe2O3, giving aluminium oxide and iron.
(e) Barium chloride reacts with zinc sulphate to give zinc chloride and barium sulphate.
Answers :
(a) 2H2S + 3O2 → 2H2O + 2SO2
(b) P4 + SO2 → 2P2O5
(c) CS2 + 3O2 → CO2 + 2SO2
(d) 2Al + Fe2O3 → Al2O3 + 2Fe
(e) BaCl2 + ZnSO4 → ZnCl2 + BaSO4
11. Write the balanced chemical equations fo the following reactions :
16. Fill in the following blanks with suitable words :
(a) Chemical equations are balanced to satisfy the law of .................
(b) A solution made in water is known as an ............. solution and indicated by the symbol ............
Answers :
(a) Chemical equations are balanced to satisfy the law of conservation of mass.
(b) A solution made in water is known as an aqueous solution and indicated by the symbol (aq).
Short Answer Type Questions - Page no 19 & 20
17. (a) Give one example of a chemical reaction.
(b) State two characteristics of the chemical reaction which takes place when dilute sulphuric acid is poured over zinc granules.
(c) Give two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution.
Answers :
(a) Rusting of iron
(b) The two characterisitcs are :
Evolution of hydrogen gas
Rise in temperature
(c) The two characteristics are :
Change in colour
Formation of precipitate
18. (a) What is chemical equation ? Explain with the help of an example.
(b) Giving examples, state the difference between balanced and unbalanced chemical equations.
(c) Balance the following chemical equations :
(i) NH3 → N2 + H2
(ii) C + CO2→ CO
Answers :
(a) The method of representing a chemical reaction with the help of symbols and formulae of the substances involved in its is known as a chemical equation. For example, zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.
It can be written as : Zn + H2SO4→ ZnSO4 + H2
(b) Difference between balanced and unbalanced chemical equations :
Balanced chemical equation - A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. For ex : Zn + H2SO4 → ZnSO4 + H2
Unbalanced chemical equation - An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. For ex : H2 + O2 → H2O
(c) (i) 2NH3 → N2 + 3H2
(ii) C + CO2 → 2CO
19. When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are :
(i) elements (ii) compounds (iii) reactants (iv) products (v) metals (vi) non-metals
Answers :
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) metals : Cu
(vi) non - metals : H2
20. (a) What are the various ways in which a chemical equation can be made more informative ? Give examples to illustrate your answe.
(b) Write balanced chemical euation from the following information :
An aqueous calcium hydroxide solution (lime water) reacts with carbon dioxide gas to produce a solid calcium carbonate precipitate and water.
Answers :
(a) The chemical equation can be made more informative in three ways :
By indicating the "physical states" of the reactants and products.
By indicating the "heat changes" taking place in the reaction.
By indicating the "conditions" under which the reaction takes place.
21. (a) What is a balanced chemical equation ? Why should chemical equations be balanced ?
(b) Aluminium burns in chlorine to form aluminium chloride (AlCl3). Write a balanced chemical equation for this reaction.
(c) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Write a balanced chemical equation for this reaction.
Answers :
(a) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. The chemical equations are balanced to satisfy the law of conservation of mass in chemical reactions.
(b) 2Al + 3Cl2 → 2AlCl3
(c) 2K + 2H2O → 2KOH + H2
22. (a) Explain, with example, how the physical states of the reactants and products can be shown in a chemical equation.
(b) Balance the following equation and add state symbols :
Zn + HCl → ZnCl2 + H2
(c) Convey the following information in the form of a balanced chemical equation :
"An aqueous solution of ferrous sulphate reacts with an aqueous solution of sodium hydroxide to form a precipitate of ferrous hydroxide and sodium sulphate remains in solution."
Answers :
(a) There can be four physical states for the reactants and products of a chemical reaction : solid, liquid, aqueous and gas.
26. Carbon monoxide reacts with hydrogen under certain conditions to form methanol (CH3OH). Write a balanced chemical equation for this reaction indicating the physical states of reactants and products as well as the conditions under which this reaction takes place.
Answer :
27. (a) Potassium chlorate (KClO3) on heating forms potassium chloride and oxyegn. Write a balanced equation for this reaction and indicate the evolution of gas.
(b) Rewrite the following information in the form of a balanced chemical equation :
Magnesium burns in carbon dioxide to form magnesium oxide and carbon.
Answers :
(a) KClO3 (s)→ 2KCl (s) + 3O2 (g)
(b) 2Mg + CO2 → 2MgO + C
28. (a) Substitute formulae for names and balance the the following equation :
Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide gas.
(b) Write balanced chemical equation with state symbols for the following reaction :
Sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride solution and water.
Answers :
(a) CaCO3 + 2HCl → CaCl2 + H2O + CO2
(b) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
29. Ammonia reacts with oxygen to form nitrogen and water. Write a balanced chemical equation for this reaction. Add the state symbols for all the reactants and products.
Answer :
4NH3 (g) + 3O2 (g) → 2N2 (g) + 6H2O (l)
30. Write a balanced chemical equation for the process of photosynthesis giving the physical states of all the substances involved and the conditions of the reaction.
Answer :
31. Translate the following statement into chemical equation and then balance it :
Barium Chloride solution reacts with aluminium sulphate solution to form a precipitate of barium sulphate and aluminium chloride solution.
32. When potassium nitrate is heated, it decomposes into potassium nitrite and oxygen. Write a balanced equation for this reaction and add the state symbols for the reactants and products.
Answer :
2KNO3 (s) → 2KNO2 (s) + O2 (g)
Long Answer Type Questions, Page no - 20 & 21
33. (a) What is meant by a chemical reaction ? Explain with the help of an example.
(b) Give one example each of a chemical reaction characterised by :
(i) evolution of a gas
(ii) change in colour
(iii) formation of a precipitate
(iv) change in temperature
(v) change in state.
Answers :
(a) Chemical reactions are the process in which new substances with the new properties are formed. For example : the burning of magnesium in air to form magnesium oxide is an example of a chemical reaction.
(b) (i) evolution of gas - the chemical reaction between zinc and dilute sulphuric acid.
(ii) change in colour - the chemical reaction between citric acid and purple coloured potassium permagnate solution.
(iii) formation of a precipitate - the chemical reaction between potassium iodide and lead nitrate.
(iv) change in temperature - the chemical reaction between quicklime and water to form slaked lime.
(v) change in state - the combustion reaction of candle wax.
34. (a) State the various characteristics of chemical reactions.
(b) State one characteristics each of the chemical reaction which takes place when :
(i) dilute hydrochloric acid is added to sodium carbonate
(ii) lemon juice is added gradually to potassium permanganate solution
(iii) dilute sulphuric acid is added to barium chloride solution
(iv) quicklime is treated with water
(v) wax is burned in the form of a candle
Answers :
(a) The various characteristics of chemical reactions are :
Evolution of gas
Formation of precipitate
Change in colour
Change in temperature
Change in state
(b) (i) Evolution of gas
(ii) Change in colour
(iii) Formation of precipitate
(iv) Change in temperature
(v) Change in state
35. (a) What do you understand by exothermic and endothermic reactions ?
(b) Give one example of an exothermic reaction and one of an endothermic reaction.
(c) Which of the following are endothermic reactions and which are exothermic reactions ?
(i) Burning of natural gas
(ii) Photosynthesis
(iii) Electrolysis of water
(iv) Respiration
(v) Decomposition of calcium carbonate
Answers :
(a) Those reaction in which heat is evolved is known as exothermic reactions and those reactions in which heat is absorbed are known as endothermic reactions.
(b) Example of exothermic reaction :
C (s) + O2 (g) → CO2 (g) + Heat
Example of endothermic reaction :
N2 (g) + O2 (g) + Heat → 2NO (g)
(c) Exothermic reactions : Burning of natural gas, Respiration
Endothermic reactions : Photosynthesis , Electrolysis of water, decomposition of calcium carbonate
Multiple Choice Questions (MCQs), Page no - 21 & 22
36. One of the following does not happen during a chemical reaction. This is :
(a) Breaking of old chemical bonds and formation of new chemical bonds
(b) Formation of new substances with entirely different properties
(c) Atoms of one element change into those of another element to form new products.
(d) A rearrangement of atoms takes place to form new products
Answer :
(c) Atoms of one element change into those of another element to form new products.
37. Which of the following does not involve a chemical reaction ?
(a) digestion of food in our body
(b) process of respiration
(c) burning of candle wax when heated
(d) melting of candle wax on heating
Answer :
(d) melting of candle wax on heating
38. You are given the solution of lead nitrate. In order to obtain a yellow precipitate you should mix with it a solution of :
(a) potassium chloride (b) potassium nitride
(c) potassium sulphide (d) potassium iodide
Answer :
(d) potassium iodide
39. An acid which can decolourise purple coloured potassium permanganate solution is :
(a) sulphuric acid (b) citric acid
(c) carbonic acid (d) hydrochloric acid
Answer :
(b) citric acid
40. The chemical reaction between two substances is characterised by a change in colour from orange to green. These two substances are most likely to be :
(a) potassium dichromate solution and sulphur dioxide
(b) potassium permanganate solution and sulphur dioxide
(c) potassium permanganate solution and lemon juice
(d) potassium dichromate solution and carbon dioxide
Answer :
(a) potassium dichromate solution and sulphur dioxide
41. The chemical reaction between quicklime and water is characterised by :
(a) evolution of hydrogen gas
(b) formation of slaked lime precipitate
(c) change in temperature of mixture
(d) change in colour of the product
Answer :
(c) change in temperature of mixture
42. One of the following is an endothermic reaction. This is :
(a) Combination of carbon and oxygen to form carbon monoxide
(b) Combination of nitrogen and oxygen to form nitrogen monoxide
(c) Combination of glucose and oxygen to form carbon dioxide and water
(d) Combination of zinc and hydrochloric acid to form zinc chloride and hydrogen
Answer :
(b) Combination of nitrogen and oxygen to form nitrogen monoxide
43. Which of the following is not an endothermic reaction ?
(a) CaCO3 → CaO + CO2
(b) 2H2O → 2H2 + O2
(c) 6CO2 + 6H2O → C6H12O6 + 6O2
(d) C6H12O6 + 6O2 → 6CO2 + 6H2O
Answer :
(d) C6H12O6 + 6O2 → 6CO2 + 6H2O
44. One of the following is an exothermic reaction. This is :
(a) electrolysis of water
(b) conversion of limestone into quicklime
(c) process of respiration
(d) process of photosynthesis
Answer :
(c) process of respiration
45. The chemical equations are balanced to satisfy one of the following laws in chemical reactions. This law is known as :
(a) law of conservation of momentum
(b) law of conservation of mass
(c) law of conservation of motion
(d) law of conservation of magnetism
Answer :
(b) law of conservation of mass
Questions Based on High Order Thinking Skills (HOTS) - Page no : 22 & 23
46. When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution.
(a) What do you think substance X is likely to be ?
(b) Name the substance which the yellow solid consists of.
(c) Which characteristics of chemical reactions is illustrated by this example ?
(d) Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.
47. When water is added gradually to white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory.
(a) What could be solid X ? Write its chemical formula.
(b) What could be product Y ? Write its chemical formula.
(c) What is the common name of the solution of Y which is used for testing carbon dioxide gas ?
(d) Write chemical equation of the reaction which takes place on adding water to solid X.
(e) Which characteristics of chemical reactions is illustrated by this example ?
Answers :
(a) Calcium oxide, CaO
(b) Calcium hydroxide, Ca(OH)2
(c) Lime water
(d) CaO + H2O → Ca(OH)2
(e) Change in temperature
48. When metal X is treated with dilute acid Y, then a gas Z is evolved which burns readily by making a little explosion.
(a) Name any two metals which can behave like metal X.
(b) Name any two acids which behave like acid Y.
(c) Name the gas Z.
(d) Is the gas Z lighter than or heavier than air ?
(e) Is the reaction between metal X and dilute acid Y exothermic or endothermic ?
(f) By taking a specific example of metal X and dilute acid Y, write a balanced chemical equation for the reaction which takes place. Also indicate physical states of all the reactants and products.
Answers :
(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)
49. A solid substance P which is very hard is used in the construction of many buildings, especially flooring. When substance P is heated strongly, it decomposed to form another solid Q and gas R is given out. Solid Q reacts with water with the release of a lot of heat to form a substance S. When gas R is passed into a clear solution of substance S, then a white precipitate of substance T is formed. The substance T has the same chemical composition as starting substance P.
(a) What is substance P ? Write its common name as well as chemical formula.
(b) What is substance Q.
(c) What is gas R ?
(d) What is substance S ? What is its clear solution known as ?
(e) What is substance T ? Name any two natural forms in which substance T occurs in nature.
Answers :
(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
50. A silvery - white metal X taken in the form of ribbon, when inited, burns in air with a dazzlin white flame to form a white powder Y. When water is added to powder Y, it dissolves partially to form another substance Z.
(a) What could metal X be ?
(b) What is powder Y ?
(c) With which substance metal X combines to form powder Y ?
(d) What is substance Z ? Name one domestic use of subatance Z.
(e) Write a balanced chemical equation of the reaction which take place when metal X burns in air to form powder Y.
Answers :
(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
51. A metal X forms a salt XSO4. The salt XSO4 forms a clear solution in water which reacts with sodium hydroxide solution to form a blue precipitate Y. Metal X is used in making electric wires and allows like brass.
(a) What do you think metal X could be ?
(b) Write the name , formula and colour of salt XSO4.
(c) What is the blue precipitate Y ?
(d) Write a chemical equation of the reaction which takes place when salt XSO4 reacts with sodium hydroxide solution. Gie the state symbols of all the reactants and products which occur in the above equation.
52. The metal M reacts vigorously with water to form a solution S and a gas G. The solution S turns red litmus to blue whereas gas G, which is lighter than air, burns with a pop sound. Metal M has a low melting point and it is used as a coolant in nuclear reactors.
(a) What is metal M ?
(b) What is solution S ? Is it acidic or alkaline ?
(c) What is gas G ?
(d) Write a balanced chemical equation for the reaction which takes place when metal M reacts with water.
53. When a mixture of gases X and Y is compressed to 300 atm pressure and then passed over a catalyst consisting of a mixture of zinc oxide (heated to a temperature of 300℃), then an organic compound Z having the molecular formula CH4O is formed. X is a highly poisonous gas which is formed in appreciable amounts when a fuel burns in a limited supply of air ; Y is a gas which can be made by the action of a dilute acid on an active metal ; and Z is a liquid organic compound which can react with sodium metal to produce hydrogen gas.
(a) What are X, Y and Z ?
(b) Write a balanced chemical equation of the reaction which takes place when X and Y combine to form Z. Indicate the conditions under which the reaction occurs.
Answers :
(a) X is carbon monoxide gas (CO) ; Y is hydrogen gas (H2) ; Z is methanol (or Methyl alcohol) (CH3OH)
(b)
54. The white solid compound A decomposes quite rapidly on heating in the presence of a black substance X to form a solid compound B and gas C. When an aqueous solution of compound B is reacted with silver nitrate solution, then a white precipitate of silver chloride is obtained alongwith potassium nitrate solution. Gas C does not burn itself but helps burn other things.
(a) What is compound A ?
(b) What is compound B ?
(c) What is gas C ?
(d) What do you think is the black substance X ? What is its function ?
(e) What is the general name of substances like X ?
Answers :
(a) Potassium chlorate, KClO3
(b) Potassium chloride, KCl
(c) Oxygen, O2
(d) Maganese dioxide, MnO2 ; It acts as a catalyst in the decomposition of potassium chlorate to form oxygen gas
(e) Catalysts
55. Gas A, which is the major cause of global warming, combines with hydrogen oxide B in nature in the presence of an environmental factor C and a green material D to form a six carbon organic compound E and a gas F. The gas F is necessary for breathing.
(a) What is gas A ?
(b) What is the common name of B ?
(c) What do you think could be C ?
(d) What is material D ? Where is it found ?
(e) Name the organic compound E.
(f) What is gas F ? Name the natural process during which it is released.
Answers :
(a) Carbon dioxide, CO2
(b) Water, H2O
(c) Sunlight
(d) Chlorophyll ; Green leaves of plants
(e) Glucose, C6H12O6
(f) Oxygen ; Photosynthesis
Very Short Answer Type Questions, Page no - 45
1. What type of reaction is represented by the digestion of food in our body ?
Answer :
Decomposition reaction
2. Name the various types of chemical reactions.
Answer :
Combination reactions
Decomposition reactions
Displacement reactions
Double displacement reactions
Oxidation & reduction reactions
3. Why does the colour of copper sulphate solution change when an iron nail is kept immersed in it ?
Answer :
4. Write the balanced chemical equation for the following reaction :
Zinc + Silver nitrate → Zinc nitrate + Silver
Answer :
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
5. Which term is used to indicate the development of unpleasant smell and taste in fat and oil containing foods due to aerial oxidation (when they are kept exposed for a considerable time) ?
Answer :
Rancidity
6. What is the general name of the chemicals which are added to fat and oil containing foods to prevent the development of rancidity ?
Answer :
Anti - oxidants
7. State an important use of decomposition reactions.
Answer :
The decomposition reactions carried out by electricity are used to extract several metals from their naturally occuring compounds like chlorides and oxides.
8. What are anti - oxidants ? Why are they added to fat and oil containing foods ?
Answer :
Anti - oxidants are the substance (or chemical) which prevents oxidation. Actually, anti - oxidants are reducing agents. It is added to prevent rancidity in foods containing fats and oils.
9. Explain why, food products containing fats and oils (like potato chips) are packaged in nitrogen.
Answer :
When the packed food is surrounded by the unreactive nitogrn gas, there is no oxygen to cause its oxidation and makes it rancid. That's why it is packed in nitrogen.
10. Give one example of a decomposition reaction which is carried out :
(a) with electricity
(b) by applying heat
Answers :
11. What tpe of chemical reaction is used to extract metals from their naturally occuring compounds like oxides or chlorides ?
Answer :
Decomposition reactions (carried out by electricity)
12. Name two anti - oxidants which are usually added to fat and oil containing foods to prevent rancidity.
13. Write one equation each for the decomposition reactions where energy is supplied in the form of (a) heat, (b) light, and (c) electricity.
Answers :
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the chemical euation of the reaction involved.
Answer :
2AgNO3 (aq) + Cu (s) → Cu(NO3)2 (aq) + 2Ag (s)
15. What type of reactions are represented by the following equations ?
(i) CaCO3 → CaO + CO2
(ii) CaO + H2O → Ca(OH)2
(iii) 2FeSO4 → Fe2O3 + SO2 + SO3
(iv) NH4Cl → NH3 + HCl
(v) 2Ca + O2 → 2CaO
Answers :
(i) Decomposition reaction
(ii) Combination reaction
(iii) Decomposition reaction
(iv) Decomposition reaction
(v) Combination reaction
16. What type of chemical reactions take place when :
(a) a magnesium wire is burnt in air ?
(b) lime - stone is heated ?
(c) silver bromide is exposed to sunlight ?
(d) electricity is assed through water ?
(e) ammonia and hydrogen chloride are mixed ?
Answers :
(a) Combination reaction
(b) Decomposition reaction
(c) Decomposition reaction
(d) Decomposition reaction
(e) Combination reaction
17. What type of chemical reactions are represented by the following equations ?
(i) A + BC → AC + B
(ii) A + B → C
(iii) X → Y + Z
(iv) PQ + RS → PS + RQ
(v) A2O3 + 2B → B2O3 + 2A
Answers :
(i) Displacement reaction
(ii) Combination reaction
(iii) Decomposition reaction
(iv) Double displacement reaction
(v) Displacement reaction
18. Balance the following chemical equations :
Answers :
19. Which of the following is a combination and which is a displacement reaction ?
(a) Cl2 + 2KI → 2KCl + I2
(b) 2K + Cl2 → 2KCl
Answers :
(a) Displacement reaction
(b) Combination reaction
20. What type of reactions are represented by the following equations ?
(a) CaO + CO2 → CaCO3
(b) 2Na + 2H2O → 2NaOH + H2
(c) Mg + CuSO4 → MgSO4 + Cu
(d) NH4NO2 → N2 + 2H2O
(e) CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4
Answers :
(a) Combination reaction
(b) Displacement reaction
(c) Displacement reaction
(d) Decomposition reaction
(e) Double displacement reaction
21. In the following reaction between lead sulphide and hydrogen peroxide :
PbS (s) + 4H2O2 (aq) → PbSO4 (s) + 4H2O (l)
(a) Which substance is reduced ?
(b) Which substance is oxidised ?
Answers :
(a) H2O2
(b) PbS
22. Identify the component oxidised in the following reaction :
H2S + Cl2 → S + 2HCl
Answer :
H2S
23. When SO2 gas is passed through saturated solution of H2S, the following reaction occurs :
SO2 + 2H2S → 2H2O + 3S
In this reaction, which substance is oxidised and which one is reduced ?
Answer :
Substance oxidised : H2S, Substance reduced : SO2
24. Fill in the following blanks with suitable words :
(a) The addition of oxygen to a substance is called ............... whereas removal of oxygen is called ..........
(b) The addition of hydrogen to a substance is called .................. whereas removal of hydrogen is called ................
(c) Anti - oxidants are often added to fat containing foods to prevent ................. due to oxidation.
Answers :
(a) oxidation ; reduction
(b) reduction ; oxidation
(c) rancidity
Short Answer Type Questions, Page no - 46 & 47
25. What is an oxidation reaction ? Identify in the following reaction (i) the substance oxidised, and (ii) the substance is reduced :
ZnO + C → Zn + CO
Answers :
(i) C (ii) ZnO
26. (a) What is a redox reaction ? Explain with an example.
(b) When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced ? Why ?
(c) In the reaction represented by the equation :
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
(i) name the substance oxidised
(ii) name the oxidising agent
(iii) name the substance reduced.
(iv) name the reducing agent.
Answers :
(a) In the name 'redox' , the term 'red' stands for 'reduction' and 'ox' stands for oxidation. So, the oxidation and reduction reactions are called redox reactions.
(b) Magnesium is oxidised, because addition of oxygen to magnesium takes place.
(c) (i) HCl
(ii) MnO2
(iii) MnO2
(iv) HCl
27. (a) Define a combination reaction.
(b) Give one example of a combination reaction which is also exothermic.
(c) Give one example of a combination reaction which is also endothermic.
Answers :
(a) Those reactions in which two or more substances combine to form a single substance, are called combination reactions.
(b) C (s) + O2 (g) → CO2 + Heat (Burning of carbon in the presence of oxygen to produce carbon dioxide)
(c) N2 (g) + O2 (g) + Heat → 2NO (g)
28. (a) Give an example of an oxidation reaction.
(b) Is oxidation an exothermic or an endothermic reaction ?
(c) Explain, by giving an example, how oxidation and reduction proceed side by side.
Answers :
(a)
(b) Oxidation is an exothermic reaction.
29. (a) What is the colour of ferrous sulphate crystals ? How does this colour change after heating ?
(b) Name the product formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change ?
Answers :
(a) The colour of ferrous sulphate is green. The colour changes green to brown after heating.
(b) The product formed on strongly heating ferrous sulphate crystals is a smell of burnin sulphur is obtained due to the formation of sulphur dioxide gas. Decomposition reaction occurs in this change.
30. What is a decomposition reaction ? Give an example of a decomposition reaction. Describe an activity to illustrate such a reaction by heating.
Answers :
Those reactions in which a compound splits up into two or more simpler substances are known as decomposition reactions.
In this reaction, one substance, calcium carbonate, is breaking up into two simpler substances, calcium oxide and carbon dioxide. The decomposition of calcium carbonate (limestone) on heating is an important reaction used in various industries. This is because calcium oxide (lime) obtained by the decomposition of calcium carbonate has many uses in industry. For example, calcium oxide (or lime) is used on a large scale in the manufacture of cement and glass.
31. Zinc oxide reacts with carbon, on heating, to form zinc metal and carbon monoxide. Write a balanced chemical equation for this reaction. Name (i) oxidising agent, and (ii) reducing agent, in this reaction.
Answers :
(i) oxidising agent : Zinc oxide
(ii) reducing agent : Carbon
32. Give one example of an oxidation - reduction reaction which is also :
(a) a combination reaction
(b) a displacement reaction
Answers :
(a) a combination reaction
(b) a displacement reaction
33. (a) What is the difference between displacement and double displacement reactions ? Write equations for these reactions.
(b) What do you mean by a precipiation reaction ? Explaining giving an example.
Answers :
(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions. Eqation for these reaction :
Those reaction in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions. Equation for this reaction :
(b) Any reaction in which an insoluble solid (called precipitate) is formed that separates from the solution is called a precipitation reaction. For ex : If barium chloride solution is added to copper sulphate solution, then a white precipitate of barium sulphate is produed alongwith copper chloride solution.
34. (a) Explain the following in terms of gain or loss of oxygen with one example each : (i) oxidation (ii) reduction
(b) When copper powder is heated strongly in air, it forms copper oxide. Write a balanced chemical equation for this reaction. Name (i) substance oxidised, and (ii) substance reduced.
Answers :
(a) (i) The addition of oxygen to a substance is called oxidation. For ex :
(ii) The removal of oxygen from a substance is called reduction. For ex :
35. (a) Define the following in terms of gain or loss of hydrogen with one example each : (i) oxidation (ii) reduction
(b) When a magnesium ribbon is heated, it burns in air to form magnesium oxide. Write a balanced chemical equation for this reaction. Name (i) substance oxidised, and (ii) substance reduced.
Answers :
(a) (i) oxidation : The removal of hydrogen from a substance is called oxidation. For ex :
(ii) reduction : The addition of hydrogen to a substance is called reduction. For ex :
36. What is meant by (a) displacement reaction, and (b) double displacement reaction ? Explain with the help of one example each.
Answers :
(a) Those reactions in which one element takes the place of another element in a compound, are known as displacment reactions. For ex :
(b) Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions. For ex :
37. (a) Why are decomposition reactions called the opposite of combination reactions ? Explain with equations of these reactions.
(b) Express the following facts in the form of a balanced chemical equation :
"When a strip of copper metal is placed in a solution of silver nitrate, metallic silver is precipitated and a solution containing copper nitrate is formed".
Answers :
(a) In combination reaction, two or more substances combine to form a single substance whereas in decomposition reaction, a compound splits up into two or more simpler substances. For ex :
(b) Cu (s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s)
38. (a) What happens when a piece of iron metal is placed in copper sulphate solution ? Name the type of reaction involed.
(b) Write balanced chemical equation with state symbols for the following reaction :
Barium chloride solution reacts with sodium sulphate solution to give insoluble barium sulphate and a solution of sodium chloride.
Answers :
(a) When a piece of iron metal is placed in copper sulphate solution, then iron sulphate solution and copper metal are formed :
The type of reaction involved is : Displacement reaction.
(b)
39. In the reaction represented by the following equation :
CuO (s) + H2 (g) → Cu (s) + H2O (l)
(a) name the substance oxidised
(b) name the substance reduced
(c) name the oxidising agent
(d) name the reducing agent
Answers :
(a) H2
(b) CuO
(c) CuO
(d) H2
40. What happens when silver nitrate solution is added to sodium chloride solution ?
(a) Write the equation for the reaction which takes place.
(b) Name the type of reaction involved.
Answers :
When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed alongwith sodium nitrate solution.
It is a double displacement reaction.
41. What happens when silver chloride is exposed to sunlight ? Write a chemical equation for this reaction. Also give one use of such a reaction.
Answers :
When silver chloride is exposed to sunlight, it decomposes to form silver metal and chlorine gas.
This reaction is used in black and white photography.
42. What happens when a zinc strip is dipped into a copper sulphate solution ?
(a) Write the equation for the reaction that takes place.
(b) Name the type of reaction involved.
Answers :
When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained.
(b) It is displacement reaction.
Long Answer Type Questions, Page no - 48
43. (a) Explain the term "corrosion" with an example. Write a chemical equation to show the process of corrosion of iron.
(b) What special name is given to the corrosion of iron ?
(c) What type of chemical reaction is involved in the corrosion of iron ?
(d) Name any three objects (or structures) which are gradually damaged by the corrosion of iron and steel.
Answers :
(a) Corrosion is the process of 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 if corrosion.
(b) Rusting
(c) Oxidation
(d) Railings, car bodies & bridges
44. (a) Explain the term "rancidity". What damage is caused by rancidity ?
(b) What type of chemical reaction is responsible for causing rancidity ?
(c) State and explain the various methods for preventing or retarding rancidity of food.
Answers :
(a) The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called rancidity. Rancidity 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 reaction is responsible for causing rancidity.
(c) The development of rancidity of food can be prevented or retarded (slowed down) in the following ways :
Rancidity can be prevented by adding anti - oxidants to foods containing fats and oils.
Rancidity can be prevented by packaging fat and oil containing foods in nitrogen gas.
Rancidity can be retarted by keeping food in a refrigerator.
Rancidity can be retarted by storing food in air - tight containers.
Rancidity can be retarted by storing foods away from light.
45. (a) What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride ?
(b) Write the balanced chemical equation for the reaction which takes place.
(c) State the physical conditions of reactants in which the reaction will not take place.
(d) Name the type of chemical reaction which occurs.
(e) Give one example of another reaction which is of the same type as the above reaction.
Answers :
(a) When aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride, then a white precipitate of barium sulphate is formed alongwith sodium chloride solution.
(c) Solid sodium sulphate and Solid barium chloride
(d) Double displacement reaction
(e) Double displacement reaction between silver nitrate solution and sodium chloride solution to form a white precipitate of silver chloride and sodium nitrate solution.
Multiple Choice Questions (MCQs), Page no - 48
46. The removal of oxygen from a substance is called :
(a) oxidation
(b) corrosion
(c) reduction
(d) rancidity
Answer : (c) reduction
47. In the context of redox reactions, the removal of hydrogen from a substance is known as :
(a) oxidation
(b) dehydration
(c) reduction
(d) dehydrogenation
Answer : (a) oxidation
48. The chemical reaction involved in the corrosion of iron metal is that of :
(a) oxidation as well as displacement
(b) reduction as well as combination
(c) oxidation as well as combination
(d) reduction as well as displacement
Answer : (c) oxidation as well as combination
49. The term used to indicate the development of unpleasant smell and taste in fat and oil containing foods due to aerial oxidation is :
(a) acidity
(b) radioactivity
(c) rabidity
(d) rancidity
Answer : (d) rancidity
50. In order to prevent the spoilage of potato chips, they are packed in plastic bags in an atmosphere of :
(a) Cl2
(b) H2
(c) N2
(d) O2
Answer : (c) N2
51. A white precipitate can be obtained by adding dilute sulphuric acid to :
(a) CuSO4 solution
(b) NaCl solution
(c) BaCl2 solution
(d) Na2SO4 solution
Answer : (c) BaCl2 solution
52. A white precipitate will be formed if we add common salt solution to :
(a) Ba(NO3)2 solution
(b) KNO3 solution
(c) AgNO3 solutiom
(d) Mg(NO3)2 solution
Answer : (c) AgNO3 solutiom
53. Consider the following equation of the chemical reaction of a metal M :
4M + 3O2 → 2M2O3
This equation represents :
(a) combination reaction as well as reduction reaction
(b) decomposition reaction as well as oxidation reaction
(c) oxidation reaction as well as displacement reaction
(d) combination reaction as well as oxidation reaction
Answer : (d) combination reaction as well as oxidation reaction
54. The process of respiration is :
(a) an oxidation reaction which is endothermic
(b) a reduction reaction which is exothermic
(c) a combination reaction which is exothermic
(d) an oxidation reaction which is exothermic
Answer : (d) an oxidation reaction which is exothermic
55. Which of the following can be decomposed by the action of light ?
(a) NaCl
(b) KCl
(c) AgCl
(d) CuCl
Answer : (c) AgCl
56. Consider the reaction :
KBr (aq) + AgNO3 (aq) → KNO3 (aq) + AgBr (s)
This is an example of :
(a) decomposition reaction
(b) combination reaction
(c) double displacement reaction
(d) displacement reaction
Answer : (c) double displacement reaction
57. You are given the following chemical equation :
Mg (s) + CuO (s) → MgO (s) + Cu (s)
This equation represents :
(a) decomposition reaction as well as displacement reaction
(b) combination reaction as well as double displacement reaction
(c) redox reaction as well as displacement reaction
(d) double displacement reaction as well as redox reaction
Answer : (c) redox reaction as well as displacement reaction
Questions Based on High Order Thinking Skills (HOTS) - Page no, 49
58. When a green iron salt is heated strongly, its colour finally changes to brown and odour of burning sulphur to given out.
(a) Name the iron salt
(b) Name the type of reaction that takes place during the heating of iron salt.
(c) Write a chemical equation for the reaction inolved.
Answers :
(a) Ferrous sulphate
(b) Decomposition reaction
59. A colourless lead salt, when heated, produces a yellow residue and brown fumes.
(a) Name the lead salt
(b) Name the brown fumes.
(c) Write a chemical equation of the reaction involved.
Answers :
(a) Lead nitrate
(b) Nitrogen dioxide
60. When hydrogen burns in oxygen, water is formed and when water is electrolysed, then hydrogen and oxygen are produced. What type of reaction takes place :
(a) in the first case ?
(b) in the second case ?
Answers :
(a) Combination reaction
(b) Decomposition reaction
61. A strip of metal X is dipped in a blue coloured salt solution YSO4. After some time, a layer of metal Y from the salt solution is formed on the surface of metal strip X. Metal X is used in galvanisation whereas metal Y is used in making electric wires. Metal X and metal Y together form an alloy Z.
(a) What could metal X be ?
(b) What could metal Y be ?
(c) Name the metal salt YSO4
(d) What type of chemical reaction takes place when metal X reacts with salt solution YSO4 ? Write the equation of the chemical reaction involved.
(e) Name the alloy Z.
Answers :
(a) Zinc (Zn)
(b) Copper (Cu)
(c) Copper sulphate (CuSO4)
(d)
Displacement Reaction
(e) Brass
62. When a black metal compound XO is heated with a colourless gas Y2, then metal X and another compound Y2O are formed. Metal X is red - brown in colour which doesn't react with dilute acids at all. Gas Y2 can be prepared by the action of a dilute acid on any active metal. The compound Y2O is a liquid at room temperature which can turn anhydrous copper sulphate blue.
(a) What do you think is metal X ?
(b) What could be gas Y2 ?
(c) What is compound XO ?
(d) What is compound Y2O ?
(e) Write the chemical equation of the reaction which takes place on heating XO with Y2.
(f) What type of chemical reaction is illustrated in the above equation ?
Answers :
(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)
63. A metal X forms a water soluble salt XNO3.When an aqueous solution of XNO3 is added to common salt solution, then a white precipiate of compound Y is formed alongwith sodium nitrate solution. Metal X is said to be the best conductor of electricity and it does not evolve hydrogen when put in dilute hydrochloric acid.
(a) What is metal X ?
(b) What is salt XNO3 ?
(c) Name the compound Y.
(d) Write the chemical equation of the reaction which takes place on reacting XNO3 solution and common salt solution giving the physical states of all the reactants and products.
(e) What type of chemical reaction is illustrated by the above equation ?
64. Two metals X and Y form the salts XSO4 and Y2SO4, respectively. The solution of salt XSO4 is blue in colour whereas that of Y2SO4 is colourless. When barium chloride solution is added to XSO4 solution, then a white precipitate Z is formed alongwith a salt which turns the solution green. And when barium chloride solution is added to Y2SO4 solution, then the same white precipiate Z is formed alongwith colourless common salt solution.
(a) What could the metal X be ?
(b) Write the name and formula of XSO4 .
(c) Write the name and formula of salt Y2SO4.
(d) What is the name and formula of white precipitate Z ?
(e) Write the name and formula of the salt which turns the solution green in the first case.
Answers :
(a) Metal X : Copper ; Metal Y : Sodium
(b) Copper sulphate, CuSO4
(c) Sodium sulphate, Na2O4
(d) Barium sulphate, BaSO4
(e) Copper chloride, CuCl2
65. A red - brown metal X forms a salt XSO4. When hydrogen sulphide gas is passed through an aqueous solution of XSO4, then a black precipitate of XS is formed alongwith sulphuric acid solution.
(a) What could the salt XSO4 be ?
(b) What is the colour of salt XSO4 ?
(c) Name the black precipiate XS.
(d) By using the formula of salt obtained in (a) above, write an equation of the reaction which takes place when hydrogen sulphide gas is passed through its aqueous solution.
(e) What type of chemical reaction takes place in this case ?
Answers :
(a) Copper sulphate
(b) Blue colour
(c) Copper sulphide
(d) CuSO4 (aq) + H2S (g) → CuS (s) + H2SO4 (aq)
(e) Double displacement reaction
66. When a strip of red - brown metal X is placed in colourless salt solution YNO3 then metal Y is set free and a blue coloured salt solution X(NO3)2 is formed. The liberated metal Y forms a shining white deposit on the strip of metal X.
(a) What do you think metal X is ?
(b) Name the salt YNO3.
(c) What could be metal Y ?
(d) Name the salt X(NO3)2.
(e) What type of reaction takes place between metal X and salt solution YNO3 ?
Answers :
(a) Copper
(b) Silver nitrate
(c) Silver
(d) Copper nitrate
(e) Displacement reaction
67. A metal salt MX when exposed to light splits up to form metal M and a gas X2. Metal M is used in making ornaments whereas gas X2 is used in making bleaching powder. The salt MX is itself used in black and white photography.
(a) What do you think metal M is ?
(b) What could be gas X2 ?
(c) Name the metal salt MX ?
(d) Name any two salt solutions which on mixing together can produce a precipitate of salt MX.
(e) What type of chemical reaction takes place when salt MX is exposed to light ? Write the equation of the reaction.
