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.
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Page no: 18
In-text questions set 1
Very Short Answer Type Questions
1. Why is respiration considered an exothermic process?
Solution:
An exothermic reaction is a reaction in which the energy is liberated. In the process of respiration, energy is released and thus considered as an exothermic reaction
2. On what basis is a chemical equation balanced?
Solution:
A chemical equation is always balanced by comparing the number of atoms of each element on the reactant side as well as the product side. It is based on the Law of conservation of mass, i.e. number of atoms on the left-hand side should be equal to the right-hand side
3. What happens chemically when quicklime is added to water filled in a bucket?
Solution:
Quick lime is chemically calcium oxide. When it is added to water filled in a bucket, it forms calcium hydroxide (slaked lime) and reacts vigorously by releasing a large amount of heat which is an exothermic reaction.
4. Why should magnesium ribbon be cleaned before burning in the air?
Solution:
Magnesium ribbon is made up of pure magnesium metal, and it is highly reactive with oxygen which further leads to the oxidation of magnesium when it comes in contact with air. On the surface of the magnesium ribbon, it forms a layer of oxide and acts as a protective layer. So it is necessary to clean the magnesium ribbon before burning in the air
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.
Solution:
False
6. What is wrong with the following chemical equation?
Mg + O → MgO
Correct and balance it.
Solution:
Oxygen should be in molecular form, O2
2Mg + O2 → 2MgO
7. What does the symbol (aq) represent in a chemical equation?
Solution:
In a chemical equation, (aq) always represents for aqueous solution
8. Why is photosynthesis considered an endothermic reaction?
Solution:
Endothermic reactions are those in which heat is absorbed in the reaction. As we know that photosynthesis is a process that green plants and some other organisms use sunlight to synthesize food from carbon dioxide and water, which turns into oxygen and glucose. Plants absorb direct energy from the sun and thus consider photosynthesis as an endothermic reaction.
9. How will you indicate the following effects in a chemical equation?
(a) A solution made in water
(b) Exothermic reaction
(c) Endothermic reaction
Solution:
(a) The solution made in water can be indicated by the symbol (aq), which shows it is aqueous
(b) An exothermic reaction can be indicated by Heat, heat energy or energy on the product side
(c) An endothermic reaction can be indicated by Heat, heat energy or energy on the reactant side
10. Translate the following statements into chemical equations and then balance the equations:
(a) Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.
(b) Phosphorus burns in oxygen to give phosphorus pentoxide.
(c) Carbon disulphate burns in the 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.
Solution:
(a) 2H2S + 3O2 → 2H2O + 2SO2
(b) P4 + 5O2 → 2P2O5
(c) CS2 + 3O2 → CO2 + 2SO2
(d) 2Al + Fe2O3 → Al2O3 + 2Fe
(e) BaCl2 + ZnSO4 → ZnCl2 + BaSO4
11. Write the balanced chemical equations for the following reactions:
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Aluminium + Copper chloride → Aluminium chloride + Copper
Solution:
(a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) 2Al + 3CuCl2 → 2AlCl3 + 3Cu
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12. Complete and balance the following equations:
(a) NaOH + ______ → Na2SO4 + H2O
(b) Ca(OH)2 + _______ → CaCO3 + H2O
Solutions:
(a) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(b) Ca(OH)2 + CO2 → CaCO3 + H2O
13. Correct and balance the following equations:
(i) Ca + H2O → CaOH + H
(ii) N + H → NH3
Solutions:
(i) Ca + 2H2O → Ca(OH)2 + H2
(ii) N2 + 3H2 →2NH3
14. Write complete balanced equations for the following reactions:
(a) Calcium (solid) + Water (liquid) →Calcium hydroxide (solution) + Hydrogen (gas)
(b) Sulphur dioxide (gas) + Oxygen (gas) → Sulphur trioxide (gas)
Solutions:
(a) Ca (s) + 2H2O (l) → Ca(OH)2 (aq) + H2 (g)
(b) 2SO2 (g) + O2 (g) → 2SO3 (g)
15. Balance the following equations:
(i) Na + O2 → Na2O
(ii) H2O2→ H2O + O2
(iii) Mg(OH)2 + HCl → MgCl2 +H2O
(iv) Fe +O2 → Fe2O3
(v) Al(OH)3 → Al2O3 +H2O
(vi) NH3 + CuO → Cu +N2 +H2O
(vii) Al2(SO4)3 + NaOH → Al(OH)3 + Na2SO4
(viii) HNO3 +Ca(OH)2 → Ca(NO3)2
(ix) NaOH +H2SO4 → Na2SO4 +H2O
(x) BaCl2 + H2SO4 → BaSO4 +HCl
Solutions:
(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
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 is indicated by the symbol _______.
Solutions:
(a) Conservation of mass
(b) Aqueous; (aq)
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.
Solutions:
(a)A chemical reaction results in new substances by undergoing certain reactions and rearrangements. There will be reactants on the left-hand side and products on the right-hand side. An example of a chemical reaction is
An example of combustion is methane + oxygen forms carbon dioxide and water. This can be written as a balanced symbol equation:
CH4 + 2O2 →CO2 + 2H2O
(b) When dilute sulphuric acid is poured over zinc granules, heat will liberate thus, the reaction becomes exothermic
Hydrogen gas is evolved, which burns with a sound
(c) 2KI (aq) + Pb(NO ) (aq) → PbI (↓) + 2 KNO (aq)
When solutions of lead nitrate and potassium iodide are mixed together, a yellow precipitate of lead iodide is formed. This is an example for Double Displacement Reaction.
18. (a) What is a 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
Solutions:
(a) Chemical equations are the symbolic representation of chemical reactions in which the reactants and products are expressed in terms of chemical formulae. Reactant entities are given on the left side, and product entities are given on the right side of a chemical equation
Example: Zn + H2SO4→ZnSO4 + H2
(b) A balanced chemical equation is always energy and mass conservative, whereas an unbalanced chemical equation is neither energy nor mass conservative. A chemical equation can be written by balancing the total number of atoms of each element in reactants and products, while in unbalanced chemical equations, the total number of atoms of each element in reactants and products is not equal
Example: KClO3→KCl + 3O2 Unbalanced equation
2KCl03→2KCl + 3O2 Balanced equation
4.4
(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
Solutions:
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
20. (a) What are the various ways in which a chemical equation can be made more informative? Give examples to illustrate your answer.
(b) Write a balanced chemical equation 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.
Solutions:
(a)Ca(OH)2 (aq)+ CO2 (g)—3000°C →CaCO3(s)+H2O(l)
A chemical equation can be informative by
1) The chemical states are indicated by (s) for solids, (l) for liquids and (g) for gases and (aq) for aqueous solution
2) Temperature is written on the above arrow
3) Arrow upwards shows compound or any gas formed escaped or liberated
4)Arrow downwards shows precipitated
5) Heat is written on the reactant side to indicate exothermic, and when on the written product side, it will be endothermic
b) Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)
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.
Solution:
(a) A chemical equation can be written by balancing the total number of atoms of each element in reactants and products. A chemical equation should be balanced so that it can follow the Law of conservation of mass.
(b) 2Al + 3Cl2 → 2AlCl3
(c) 2K + 2H2O → 2KOH + H2
Page no: 20
22. (a) Explain, with an 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.”
Solution:
(a) The physical state of the reactants and products in a chemical reaction can be shown by using the letters in the round brackets if it is solid, then (s) liquid (l) gas (g) and aqueous (aq)
Example: Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)
(b) Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)
(c) FeSO4(aq) + 2NaOH (aq) → Fe(OH)2 (s) + Na2SO4 (aq)
23. Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer
Solution:
(i) Change in temperature
When calcium oxide reacts vigorously with water to produce calcium hydroxide, a large amount of heat is evolved, and thus the temperature of the system increases hence it confirms that a chemical reaction has taken place.
(ii) Gas evolution
When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide. Here carbon dioxide is a gas and thus confirms a chemical reaction
24. (a) Aluminium hydroxide reacts with sulphuric acid to form aluminium sulphate and water. Write a balanced equation for this reaction.
(b) Balance the following chemical equation:
MnO2 + HCl → MnCl2 + Cl2 + H2O
Solution:
(a) 2Al(OH)3 + 3H2SO4 → Al2(SO4)3 + 6H2O
(b) MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
25. Write the balanced chemical equations for the following reactions, and add the state symbols:
(a) Magnesium carbonate reacts with hydrochloric acid to produce magnesium chloride, carbon dioxide and water.
(b) Sodium hydroxide reacts with sulphuric acid to produce sodium sulphate and water.
Solution:
(a) MgCO3 (s) + 2HCl (aq) →MgCl2 (aq) + CO2 (g) + H2O (l)
(b) 2NaOH (aq) + H2SO4 (aq) →Na2SO4 (aq) + 2H2O (l)
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.
Solution:
CO(g) + 2H2(g) → CH3OH
Pressure: 300atm
Temperature: 300℃
Catalyst: zinc oxide and chromium oxide
27. (a) Potassium chlorate (KClO3), on heating, forms potassium chloride and oxygen. 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.
Solution:
(a) 2KClO3 (s) → 2KCl (s) + 3O2 (g)
(b) 2Mg + CO2 → 2MgO + C
28. (a) Substitute formulae for names and balance the following equations:
Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide gas.
(b) Write a 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.
Solutions:
(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.
Solution:
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.
Solution:
6CO2 (g) + 6H2O (l) → C6H12O6 (aq.) + 6O2 (g) in the presence of sunlight
31. Translate the following statement into a 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’.
Solution:
3BaCl2 (aq) + Al2(SO4)3 (aq) → 3BaSO4 (s) + 2AlCl3 (aq)
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 of the reactants and products.
Solution:
2KNO3 (s)→ 2KNO2 (s) + O2 (g)
Long answer type questions
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
Solutions:
(a) A chemical reaction results in new substances by undergoing certain reactions and rearrangements. There will be reactants on the left-hand side and products on the right-hand side.
An example of combustion is methane + oxygen forms carbon dioxide and water. This can be written as a balanced symbol equation:
CH4 + 2O2 →CO2 + 2H2O
(b) (i) Evolution of gas
The reaction of Zinc and Hydrochloric acid
Zn + 2HCl → ZnCl2 + H2(g)
Hydrogen gas is released in the form of a diatomic molecule
(ii) Change in colour
Cu(s) + O2(g) + H2O → Cu(OH)2(s) + O2(g)
Copper is reddish brown in colour, and when it reacts with oxygen and water, it forms hydrated copper carbonate, which is green in colour
(iii) Formation of precipitate
AgNO3(aq) + KCl(aq) →AgCl(s) + KNO3
When silver nitrate and potassium chloride in their aqueous form react, a precipitate of potassium nitrate is obtained
(iv) Change in temperature
CaO + H20 →Ca(OH)2
When Quick lime is added to water to form slaked lime, a change in temperature is obtained as it reacts vigorously and produces heat which is an exothermic reaction
(v) Change in state
NH3(g) + HCl(g) → NH4Cl(s)
Ammonia and Hydrogen chloride gas reacts to form Ammonium chloride, which is a solid
Page no: 21
34. (a) State the various characteristics of chemical reactions.
(b) State one characteristic of each of the chemical reactions which take place when:
(i) Dilute hydrochloric acid is added to sodium carbonate
(ii) Lemon juice is added gradually to the 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
Solution:
(a) A chemical reaction is a reaction that takes place to form a new substance by reacting with reactants. It is characterised by the Evolution of a gas, Change in colour, Formation of a precipitate, Change in temperature, and Change in the state.
(b) (i) Evolution of Carbon dioxide gas
(ii) Change in colour from purple to colourless
(iii) Formation of a white precipitate of Barium sulphate
(iv) Change in temperature, an exothermic reaction
(v) Change in state from solid to liquid and gas
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
Solution:
(a)Exothermic reaction is a reaction that takes place when energy is released from the system into the surroundings
Endothermic reaction is a reaction that takes place when energy is absorbed from surroundings in the form of heat
(b) The thermal decomposition of Limestone
CaCO3(s)→CaO (s)+CO2(g) This is an example for endothermic reaction
Burning of fuel is an example of the exothermic reaction
C8H18(l)+25O2(g)→16CO2(g)+18H2O (g)+heat
(c) (i) and (iv) are exothermic reactions. (ii),(iii),(v) are endothermic reactions
Multiple Choice Questions (MCQs)
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
Solution:
Option (c) is the answer. Atoms of one element do not change into another element to form products, but the bonds between these atoms will break and form products, and atoms are rearranged also.
37. Which one 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
Solution:
Option (d) is the answer. Wax changes its physical state on heating but not the properties, so it does not involve any chemical change but involves physical change
38. You are given the solution of lead nitrate. In order to obtain a yellow precipitate, you should mix it with a solution of
(a) Potassium chloride
(b) Potassium nitride
(c) Potassium sulphide
(d) Potassium iodide
Solution:
Option (d) is the answer. When a solution of lead nitrate reacts with potassium iodide, it gives a yellow precipitate of lead iodide
39. An acid which can decolourise purple-coloured potassium permanganate solution is :
(a) Sulphuric acid
(b) Citric acid
(d) Carbonic acid
(d) Hydrochloric acid
Solution:
Option (b) is the answer. The reaction of purple-coloured potassium permanganate with citric acid is characterised by change in colour from purple to colourless
40. The chemical reaction between the 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
Solution:
Option (a) is the answer. The reaction between potassium dichromate and sulphur dioxide is characterised by change in colour. The orange colour of acidified potassium dichromate will change into green by passing 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
Solution:
Option (c) is the answer. The reaction of quicklime and water releases a higher amount of energy, and thus it is an exothermic reaction.
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
Solution:
Option (b) is the answer. When nitrogen and oxygen are heated at a very high temperature they form nitrogen monoxide, and it is an endothermic reaction.
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
Solution:
Option (d) is the answer. This is responsible for the respiration reaction in which glucose burns in oxygen to produce heat energy and, thus an exothermic reaction
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
Solution:
Option (c) is the answer. Respiration is an exothermic reaction as the heat energy is released, which maintains our body temperature.
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
Solution:
Option (b) is the answer. Equations are balanced when the mass of atoms of different elements in the reactants side is equal to the products side.
Questions Based on Higher Order Thinking Skills (HOTS)
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 characteristic 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.
Solution:
(a) Lead Nitrate
(b) Lead Iodide
(c) Formation of precipitate
(d)Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)
47. When water is added gradually to a white solid X, a hissing sound and a lot of heat are produced, forming a product Y. A suspension of Y in water is applied to the walls of a house during whitewashing. 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 the chemical equation of the reaction which takes place on adding water to solid X.
(e) Which characteristics of chemical reactions are illustrated by this example?
Solution:
(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 a 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 can 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 the physical states of all the reactants and products.
Solution:
(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 decomposes to form another solid Q and a 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 the 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.
Solution:
(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. Page no:23
50. A silvery-white metal X taken in the form of ribbon, when ignited, burns in air with a dazzling 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 substance Z.
(e) Write a balanced chemical equation of the reaction which takes place
When metal X burns in the air to form powder Y.
Solution:
(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 alloys 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.
Give the state symbols of all the reactants and products which occur in the above equation.
Solution:
(a) Metal could be Copper, Cu.
(b) Copper sulphate, CuSO4, Blue colour.
(c) The blue precipitate Y is Copper hydroxide, Cu(OH)2
(d) CuSO4 (aq) + 2NaOH (aq) → Cu(OH)2 (s) + Na2S04 (aq)
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.
(e) Is this reaction exothermic or endothermic?
Solution:
(a) Sodium is the metal ( Na )
(b) Solution S is Sodium hydroxide solution (NaOH solution), it is alkaline.
(c) Hydrogen, H2is the gas evolved
(d) 2Na + 2H2O → 2NaOH + H2
(e) Reaction is exothermic.
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 and chromium oxide (heated to a temperature of 300oC), 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.
Solution:
(a) X= Carbon monoxide gas (CO); Y= Hydrogen gas (H2); Z = Methanol (CH3OH or CH4O)
(b)CO(g) + 2H2(g) → CH3OH (l)
Carbon monoxide when reacts with hydrogen gas under a pressure of 300atmosphere and a temperature of 300℃ and a catalyst which is a mixture of Zinc oxide and chromium oxide
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 a gas C. When an aqueous solution of compound B is reacted with silver nitrate solution, then a white precipitate of silver chloride is obtained along with potassium nitrate solution. Gas C does not burn itself but helps burn 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 a substance like X?
Solution:
(a) Compound A is Potassium chlorate, KClO3
(b) Compound B is Potassium chloride, KCl
(c) Gas C is Oxygen, O2
(d) X is Manganese dioxide, MnO2; Manganese dioxide is used as a catalyst in order to enhance the reaction
(e) Catalysts are the general name for substances like X
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 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.
Solution:
(a) Gas A is Carbon dioxide, CO2
(b) B is Water, H2O
(c) Sunlight is the environmental factor
(d) Material D is Chlorophyll; it is found in the green leaves of plants and provides pigmentation
(e) Organic compound E is Glucose, C6H12O6
(f) F is Oxygen; Photosynthesis is the process where Oxygen is released
Very Short Answer Type Questions
Page no: 45
1. What type of reaction is represented by the digestion of food in our body?
Solution:
A decomposition reaction is a reaction which is represented by the digestion of our body it is nothing but a chemical reaction where food that we are having is further broken down into digestible nutrients such as fats, proteins and carbohydrates, which are essential for the proper functioning of a human body
2. Name the various types of chemical reactions.
Solutions:
There are many types of chemical reactions. Here are the names:
(i) Combination reactions.
(ii) Decomposition reaction.
(iii) Displacement reaction.
(iv) Double displacement reaction.
(v) Oxidation and reduction reactions.
3. Why does the colour of copper sulphate solution change when an iron nail is kept immersed in it?
Solutions:
It is a displacement reaction. Copper sulphate solution changes its colour because the iron nail dipped in the solution is more reactive than copper sulphate, and it displaces the molecules. The copper gets deposited over the nail as the copper sulphate solution becomes iron sulfate solution, and colour changes from blue to green
4. Write the balanced chemical equation for the following reaction:
Zinc + Silver nitrate Zinc nitrate + Silver
Solution:
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
5. Which term is used to indicate the development of an unpleasant smell and taste in fat and oil-containing foods due to aerial oxidation (when they are kept exposed for a considerable time)?
Solution:
Rancidity is the term used, and this condition is produced by aerial oxidation of unsaturated fat present in food and other products. It is the incomplete oxidation of fats and oils when exposed to air, light or moisture
6. What is the general name of the chemicals which are added to fat and oil-containing foods to prevent the development of rancidity?
Solution:
Anti-oxidants are the chemicals which are added to fat and oil-containing foods to slow or delay the development of rancidity. Natural Anti-oxidants are ascorbic acid ad tocopherols, whereas synthetic anti-oxidants include Butylated hydroxyanisole (BHA) and Butylated hydroxytoluene (BHT)
7. State an important use of decomposition reactions.
Solution:
The decomposition of silver chloride into silver and chlorine by light is used in photography.
In the human body, this reaction helps in the digestion of food in the stomach.
The decomposition reaction is used in the manufacture of cement and gypsum.
This reaction is used in the process of welding.
8. What are anti-oxidants? Why are they added to fat and oil-containing foods?
Solution:
Anti-oxidants are the chemicals which are added to fat and oil-containing foods to slow or delay the development of rancidity. Natural Anti-oxidants are ascorbic acid ad tocopherols, whereas synthetic anti-oxidants include Butylated hydroxyanisole (BHA) and Butylated hydroxytoluene (BHT). Anti-oxidants can be nutrients as well as enzymes that are especially proteins that can assist in the chemical reaction and prevent development such as cancer, heart attack and many other chronic diseases
9. Explain why food products containing fats and oils (like potato chips) are packaged in nitrogen.
Solution:
The packet of chips or foods containing fats and oils is flushed with nitrogen. This is because nitrogen acts as an antioxidant, and this packaging is to prevent the food products from being oxidized. If we pack it with oxygen, it reacts and becomes rancid, and the smell and taste will change and will start to decay.
10. Give one example of a decomposition reaction which is carried out:
(a) With electricity
(b) By applying heat
Solution:
(a) When electricity is passed through acidified water, it decomposes into Hydrogen and oxygen gas
2H2 O → 2H2 + O2
(b) By applying heat, thermal decomposition takes place
2NaHCO3(s) → CO2(g) + H2O(g) + Na2CO3(s)
The heating of baking soda is an example
11. What type of chemical reaction is used to extract metals from their naturally occurring compounds like oxides or chlorides?
Solutions:
Decomposition reaction is used to extract several metals from their naturally occurring compounds like oxide and chloride
Example: 2NaCl → 2Na + Cl2
12. Name two anti-oxidants which are usually added to fat and oil-containing foods to prevent rancidity.
Solution:
Anti-oxidants are used as preservatives in fat-containing foods to slow up the development of rancidity due to oxidation
Butylated hydroxytoluene (BHT) and Butylated hydroxyanisole (BHA) can also be used as anti-oxidants with greater half-life than natural anti-oxidants.
13. Write one equation each for the decomposition reactions where energy is supplied in the form of (a) heat, (b) light, and (c) electricity.
Solution:
(a) Decomposition reaction when heat is supplied
2Pb(NO3)2→ 2PbO + 4NO2 + O2
(b) Decomposition reaction when light is supplied
2AgCl → 2Ag + Cl2
(c) Decomposition reaction where electricity is supplied
2H2O→ 2H2 + O2
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the chemical equation of the reaction involved.
Solution:
2AgNO3 (aq) + Cu (s) → Cu(NO3)2 (aq) + 2Ag (s)
15. What types 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
Solution:
(i) Decomposition.
(ii) Combination.
(iii) Decomposition.
(iv) Decomposition.
(v) Combination.
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16. What type of chemical reaction stake place when:
(a) A magnesium wire is burnt in the air?
(b) Lime-stone is heated?
(c) Silver bromide is exposed to sunlight?
(d) Electricity is passed through water?
(e) Ammonia and hydrogen chloride are mixed?
Solution:
(a) Combination.
(b) Decomposition.
(c) Decomposition.
(d) Decomposition.
(e) Combination.
17. What type of chemical reaction is 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
Solution:
(i) Displacement reaction.
(ii) Combination reaction.
(iii) Decomposition reaction.
(iv) Double displacement reaction.
(v) Displacement reaction.
18. Balance the following chemical equations:
(a) FeSO4→ Fe2O3 + SO2 + SO3
(b) Pb(NO3)2(s) →PbO(s) + NO2(g) + O2
Solutions:
(a) 2FeSO4→ Fe2O3 + SO2 + SO3
(b) 2Pb(NO3)2(s) → 2PbO(s) + 4 NO2(g) + O2
Both in the presence of heat and decomposition reaction takes place
19. Which of the following is a combination, and which is a displacement reaction?
(a) Cl2 +2KI → 2KCl +I2
(b) 2K + Cl2 → 2KCl
Solution:
(a) Displacement reaction.
(b) Combination reaction.
20. What types 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
Solution:
(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 oxidized?
Solution:
(a) H2O2
(b) PbS
22. Identify the component oxidized in the following reaction:
H2S +Cl2→ S +2HCl
Solution:
H2S is oxidized in the above reaction.
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 oxidized and which one is reduced?
Solution:
In this reaction, the substance oxidised is H2S, and the substance which got reduced is SO2
24. Fill in the following blanks with suitable words:
(a) The addition of oxygen to a substance is called ______, whereas the removal of oxygen is called ______.
(b) The addition of hydrogen to a substance is called ______, whereas the removal of hydrogen is called ______.
(c) Anti-oxidants are often added to fat-containing foods to prevent ______ due to oxidation
Solution:
(a) Oxidation; reduction.
(b) Reduction; oxidation.
(c) Rancidity.
Short Answer Type Questions
25. What is an oxidation reaction? Identify in the following reaction (i) the substance oxidized, and (ii) substance reduced:
ZnO + C → Zn +CO
Solution:
Oxidation is the process by which an atom loses its electron in a reaction. Or the addition of oxygen to a substance to increase the proportion of oxygen in its molecule, and oxidation can be achieved without oxygen by the removal of hydrogen i.e. dehydrogenation.
(i)Substance oxidized is C (ii) Substance reduced is 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 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 oxidized (ii) Name the oxidizing agent
(ii) Name the substance reduced (iv) Name the reducing agent
Solutions:
(a)A redox reaction is a reaction where oxidation and reduction occur simultaneously. It is also called a redox reaction.
SO3(aq) + MnO4(aq) → SO4(aq) + Mn
Oxidation happened for SO3and reduction happened for MnO4
(b) Magnesium is oxidised as the addition of oxygen to magnesium takes place, leading to the formation of magnesium oxide.
(c) (i) HCl (ii) MnO2(iii) MnO2 (iv) HCl
Page no: 47
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.
Solution:
(a) Combination reactions are those reactions in which two or more substances combine to form a single substance or product, or two reactants combine to form one product
(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 endothermic reaction.
(b) Is oxidation an exothermic or an endothermic reaction?
(c) Explain, by giving an example, how oxidation and reduction are processed side by side.
Solution:
(a) Endothermic reaction is a reaction heat is absorbed by the reaction and example is the burning of carbon in the presence of oxygen gives carbon dioxide, and a large amount of heat is released
C (s) + O2 (g) →CO2 + Heat
(b) Oxidation is an exothermic reaction. Oxidation is a reaction in which oxygen combines with other elements, and an exothermic reaction releases energy through light or heat
(c) CuO + H2→ Cu + H2O
In this above reaction, Copper oxide is reduced to copper and hydrogen is oxidized to water
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?
Solution:
(a)Ferrous sulphate crystals are green in colour, and after heating, it becomes white because on heating, ferrous sulphate crystals lose water, and anhydrous ferrous sulphate FeSO4 is formed, so the colour changes from light green to white.
(b) On strong heating, the anhydrous sulphate decomposes to form Ferric oxide, sulphur dioxide and sulphur trioxide. This is a decomposition reaction
2FeSO4→ Fe2O3 + SO2+ SO3
30. What is a decomposition reaction? Give an example of a decomposition reaction. Describe an activity to illustrate such a reaction by heating.
Solution:
A decomposition reaction is a reaction where the compounds break down or split into two or more products. They are classified into three. Thermal decomposition, electrolytic decomposition and photodecomposition reaction
There are so many examples for decomposition reactions one of them is the decomposition of calcium carbonate into calcium oxide and carbon dioxide when heated
The decomposition reaction by heating is called the thermal decomposition reaction. Here is an example for that kind of reaction
2KClO3(s) + Heat → 2KCl + 3O2
Potassium chromate decomposes into potassium chloride, and oxygen gas is evolved.
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) oxidizing agent, and (ii) reducing agent, in this reaction.
Solution:
ZnO + C → Zn + CO
(i) Oxidizing agent is a reactant which gains electrons and is reduced during a redox reaction, and here Zinc oxide is the oxidizing agent
(ii) Reducing agent or reductant is that which substance causes another substance to reduce or it loses electrons and oxidizes in a chemical reaction. Here carbon is a reducing agent.
32. Give one example of an oxidation-reduction reaction which is also:
(a) A combination reaction
(b) A displacement reaction
Solution:
(a) 2Cu + O2 → 2CuO (Heat is given)
Copper combines with oxygen to form copper oxide, and it is an oxidation-reduction reaction
(b) CuO + H2→ Cu + H2O
Here hydrogen displaces copper to form dihydrogen oxide (Water)
33.(a) What is the difference between displacement and double displacement reactions? Write equations for these reactions.
(b) What do you mean by a precipitation reaction? Explain by giving an example.
Solution:
A displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in a displacement reaction.
An example for displacement reaction is
CuSO4 + Zn → ZnSO4+ Cu
A double displacement reaction takes place when two atoms or groups of atoms switch places to form a new compound. It generally takes place in aqueous solutions.
An example for double displacement reaction is
Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(b) Precipitation reaction is a reaction in which an insoluble solid called precipitate formed that separates from the solution.
An example is when barium chloride solution is added to sodium sulphate solution, a white precipitate of barium sulphate is formed along with the sodium chloride solution.
Na2SO4 + BaCl2 → BaSO4 + 2NaCl
34. (a) Explain the following in terms of gain or loss of Oxygen with one example each:
(i) Oxidation (ii) reduction
(b) When the 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
Solution:
(a) Oxidation is the addition of oxygen, and reduction is removing of oxygen
H2S + Cl2→ S + 2HCl
Here, hydrogen is removed from hydrogen sulphide, so it is oxidation and hydrogen sulphide is oxidized to sulphur.
(b) 2Cu + O2 → 2Cu0
(i) Cu is oxidized (ii) O2is reduced
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 the air to form magnesium oxide. Write a balanced chemical equation for this reaction. Name (i) substance oxidised, and (ii) substance reduced.
Solution:
Oxidation is the removal of hydrogen, and reduction is the gaining of hydrogen. By taking an example
Fe2O3 + 3CO → 2Fe + 3CO2
Fe got reduced here, and Carbon got oxidized by gaining oxygen
(b) 2Mg + O2→ 2MgO
(i) Substance oxidized is Mg (ii) Substance reduced is O2
36. What is meant by (a) displacement reaction, and (b) double displacement reaction? Explain with the help of one example each.
(a) Displacement reaction is a reaction in which one active element displaces a less reactive element from its salt solution
2KI + Cl2 → 2KCl + I2
(b) Double displacement reaction is a chemical change in which two ionic compounds are exchanged and makes components
Fe2O3 + 6HCl → 2FeCl3 + 3H2O
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.”
Solution:
The reactions that split or break the compounds into two simpler products are called decomposition reaction
Example: decomposition of calcium carbonate into calcium oxide and carbon dioxide when heated
CaCO3→ CaO + CO2
They are called the opposite of combination reaction because, in combination reaction, two or more reactants combine to form one single product
For example, Magnesium and oxygen combine to form magnesium dioxide
2Mg + O2→ 2MgO
(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 involved.
(b) Write a 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.
Solution:
(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.
CuSO4 + Fe → FeSO4 + Cu
(b) Na2SO4 + BaCl2 → BaSO4 + 2NaCl
39. In the reaction represented by the following equation:
(a) Name the substance oxidised
(b) Name the substance reduced
(c) Name the oxidising agent
(d) Name the reducing agent
Solutions:
(a) H2 (Addition of oxygen dihydrogen)
(b) CuO (Removal of oxygen)
(c) CuO (Being reduced)
(d) H2(Being oxidized)
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.
Solutions:
When silver nitrate solution is added to sodium chloride solution, a white precipitate of silver chloride is formed along with sodium nitrate solution.
(a)AgNO3 (aq) + NaCl (aq) → AgCl (s)+ NaNO3 (aq)
(b) Double displacement reaction is a chemical reaction where two compounds react, and the positive ions and negative ions of the two reactants switch places, forming new compounds.
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.
Solution:
When silver chloride is exposed to light, it decomposes to form silver metal and chlorine gas, which is a photolytic decomposition reaction, decomposition carried out by sunlight.
2AgCl(s) → 2Ag(s) + Cl2
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.
Solution:
Zinc sulphate Solution and copper are obtained when a strip of zinc metal is placed in copper Sulphate Solution.
(a) CuSO4(aq.) +Zn(s)→ ZnSO4(aq.) +Cu(s)
(b) Displacement reaction takes place where zinc metal displaces as zinc sulphate and copper sulphate to copper.
Long Answer Type Questions
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.
Solutions:
Corrosion is a natural process that gradually destructs the materials by chemically or by the electrochemical reaction within the environment. Corrosion occurs when most or all of the atoms on the same metal surface are oxidized and damaging the entire surface. Rusting of iron is the most common form of corrosion
4Fe + 3O2 + 2H2O → 2Fe2O3.xH2O
(b) Rusting
(c) Oxidation
(d) Statues, cars, buildings
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 the rancidity of food.
Solution:
(a)Rancidity is the process of slow oxidation of oil and fat present in the food materials resulting in the production of foul odour and taste in them. When fats and oils are oxidized, the food becomes rancid i.e., their smell and taste change.
(b)Oxidation is the chemical reaction involved in this as it gets exposed to air
(c) (i) Refrigerate cooked food at low temperatures
(ii) Pack food items in air-tight containers
(iii) Prevention by adding anti-oxidants like BHA(Butylated hydroxyanisole)
(iv) Storage of food 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.
Solution:
(a) When barium chloride solution is added to sodium sulphate solution, then a white precipitate of barium sulphate is formed along with the sodium chloride solution.
Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(c) Solid sodium sulphate and Solid barium chloride
(d) Double displacement reaction.
(e)Silver nitrate solution and sodium chloride solution forms a white precipitate of silver chloride and sodium nitrate solution.
Multiple Choice Questions (MCQs)
46. The removal of oxygen from a substance is called
(a) Oxidation
(b) Corrosion
(c) Reduction
(d) Rancidity
Solution:
Option (c) is correct. Reduction is the process of removal of oxygen from a substance and adding of hydrogen. It occurs when the oxidation of atoms decreases
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
Solution:
Option (a) is the answer. In a redox reaction, both reduction and oxidation take place, and reduction is when hydrogen is added, and oxidation is when hydrogen is removed
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
Solution:
Option (c) is the answer.
Corrosion takes place when iron metal reacts with water and oxygen and forms hydrated oxide and is an oxidation reaction as it adds up of oxygen
Iron metal combines with water and oxygen to corrode thus it is a combination reaction which further forms a single compound.
49. The term used to indicate the development of unpleasant smell and taste in fat and oil-containing food due to aerial oxidation is:
(a) Acidity
(b)Radioactivity
(c)Rabidity
(d)Rancidity
Solution:
Option (d) is the answer. Rancidity is the term used to indicate the development of unpleasant smell and taste in fat and oil-containing food due to aerial oxidation, and it can be prevented by closely and tight packing of food items in a container which does not allow air to react.
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
Solution:
Option (c) is the answer. If food items are packed in plastic bags in an atmosphere of nitrogen gas, it does not spoil as nitrogen is an inert gas and does not react with the things. This is done to prevent the oxidation of fatty acids and oils present in the chips
51. A white precipitate can be obtained by adding sulphuric acid to:
(a) CuSO4 solution
(b) NaCl solution
(c)BaCl2 solution
(d) Na2SO4 solution
Solution:
Option (c) is the answer. When dilute sulphuric acid reacts with the barium chloride, then the barium sulphate is formed as a product with hydrochloric gas and thus formed barium sulphate will be a white precipitate which is insoluble.
52. A white precipitate will be obtained if we add common salt solution to:
(a) Ba(NO3)2solution
(b) KNO3 solution
(c)AgNO3solution
(d) Mg(NO3)2 solution
Solution
Option (c) is the answer. A white precipitate is formed when we add common salt to silver nitrate, which is a precipitation reaction.
53. Consider the following equation of the chemical reaction of a metal M:
4M + 3O2→ 2M2O3
The equation represents:
(a) Combination reaction as well as the reduction reaction
(b) Decomposition reaction as well as the oxidation reaction
(c) Oxidation reaction as well as displacement reaction
(d) Combination reaction as well as the oxidation reaction
Solution
Option (d) is the answer. In the above reaction, Metal combines with oxygen to form a single compound which is a combination reaction, and here addition of oxygen takes place, so it is an 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 endothermic
(d) An oxidation reaction which is exothermic
Solution:
Option (d) is the answer. During digestion, the food that we have taken breakdown and gives energy. If we are having carbohydrate content food items, they break downs into glucose, and it combines with oxygen to give energy and thus the addition of oxygen takes place and energy is also released
55. Which of the following can be decomposed by the action of light?
(a) NaCl
(b) KCl
(c)AgCl
(d) CuCl
Solution:
Option (c) is the answer. Here AgCl is decomposed by the action of light. The reaction in which reactants split into simpler products is called a decomposition reaction, so here silver chloride can be decomposed by the action of light.
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
Solution:
Option (c) is the answer. Double displacement reaction is the given reaction that is an exchange of ions takes place between both the reactants.
57. You are given the following chemical equation:
Mg(s) + CuO(s) →MgO(s) + Cu (s)
(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
Solution:
Option(c) is the answer. Redox reaction, as well as displacement reaction, takes place because magnesium gets oxidized here, and copper reduces. Therefore it is reduction, and magnesium displaces copper in the solution as being more reactive. Thus becomes a displacement reaction.
Questions Based on Higher Order Thinking Skills
58. When a green iron salt is heated strongly, its colour finally changes to brown and the odour of burning sulphur is 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 involved.
Solution:
(a) Ferrous sulphate.
(b) Decomposition reaction.
Ferrous sulphate crystal loses water and forms anhydrous ferrous sulphate and further decomposes to form ferric oxide, sulphur dioxide and sulphur trioxide
(c) 2FeSO4→ Fe2O3 + SO2+ SO3
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.
Solution
(a) Lead nitrate is the lead salt
(b) Nitrogen dioxide is responsible for the brown fumes
(c) 2Pb(NO3)2→ 2PbO + 4NO2
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?
Solutions:
(a) Combination reaction of hydrogen and oxygen gas, which results in the formation of water
(b) Decomposition reaction is that water electrolysis which breakdown hydrogen gas and oxygen gas
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.
Solution:
(a) Metal X is Zinc (Zn)
(b)Metal Y is Copper (Cu)
(c) Copper sulphate (CuSO4) is named as YSO4
(d) Displacement reaction; Displacement reaction is a reaction in which one active element displaces a less reactive element from its salt solution
CuSO4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s)
(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 does not 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 Y 2?
(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?
Solution:
(a) Copper (Cu) will be the metal X which is red-brown in colour and does not react with dilute acids
(b) Hydrogen (H2) is the colourless gas Y2
(c) Copper oxide (CuO) will be the compound XO a black metal compound
(d) Water (H2O) is the product formed Y2O
(e) CuO + H2 →Cu + H2O
(f) Displacement reaction (which is also a redox reaction). Which one active element displaces a less reactive element from its salt solution
63 A metal X forms a water-soluble salt XNO3. When an aqueous solution of XNO3 is added to a common salt solution, then a white precipitate of compound Y is formed along with 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?
Solution:
(a) Silver (Ag) will be a metal which conducts electricity and does not evolve hydrogen when put in dilute hydrochloric acid
(b) Silver nitrate (AgNO3) is XNO3 which reacts with NaCl (common salt) to give a white precipitate
(c) Silver chloride (AgCl) is the compound Y formed, which is the white precipitate formed from the reaction of silver nitrate and sodium chloride.
(d) AgNO3(aq) + NaCl (aq)→ AgCl (s) + NaNO3 (aq)
(e) Double displacement reaction where two compounds react, and the positive ions and negative ions of the two reactants switch places, forming new compounds.
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 along with a salt which turns the solution green. And when barium chloride solution is added to Y2SO4 solution, then the same white precipitate Z is formed along with the colourless common salt solution.
(a) What could the metals X and Y be?
(b) Write the name and formula of salt 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.
Solution:
(a) Copper is Metal X, and Metal Y is Sodium. Both forms sulphate salts on the reaction
(b) Copper sulphate, CuSO4is XSO4, the salt formed which is blue in colour
(c) Sodium sulphate, Na2SO4, is Y2SO4 which is a colourless salt
(d) Barium sulphate, BaSO4 is Z which is a white precipitate formed upon the reaction when barium chloride is added to copper sulphate and turns the solution green
(e) Copper chloride, CuCl2 is the salt having a yellowish brown colour, which turns the solution green
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 along with sulphuric acid solution.
(a) What could the salt XSO4 be?
(b) What is the colour of salt XSO4?
(c) Name the black precipitate XS.
(b) By using the formula of the 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?
Solution:
(a) Copper sulphate will be the salt formed named as XSO4
(b) Blue colour is the colour of the salt as it is copper sulphate
(c) Copper sulphide is responsible for the black precipitate XS
(d) CuSO4 (aq) + H2S (g) → CuS (s) + H2SO4 (aq)
(e) Double displacement reaction in which reactant ions exchange places to form new products, which results in a precipitation reaction.
66. When a strip of red-brown metal X is placed in a 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?
Solution
(a) Copper is the metal X which is a red-brown strip
(b) Silver nitrate is the salt YNO3 which is a colourless salt solution.
(c) Silver is the metal formed Y upon the reaction of copper and silver nitrate solution thus, it forms a shining white deposit on the strip metal X
(d) Copper nitrate is X(NO3)2 the salt formed which is blue coloured as copper is present in it
(e) Displacement reaction will be the type of reaction taking place here
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
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.
Solution:
(a) Silver will be metal X
(b) Chlorine is the gas evolved when MX salt is exposed to light
(c) Silver chloride is the metal salt MX which is used in black and white photography.
(d) Silver nitrate and Sodium chloride are the two salt solutions which, on mixing together, produce a precipitate of salt silver chloride
(e) Decomposition reaction is the reaction taking place here when the compound decomposes to form simpler new products. Silver chloride decomposes to form silver and chloride gas
2AgCl → 2Ag + Cl2
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