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Class 10 Science Chapter 1 Chemical Reaction and Equations
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Chemical Reaction and Equations
Chapter – 1
GENERAL SCIENCE
TEXTUAL QUESTIONS AND ANSWERS
Page No – 6
Q.1. Why should a magnesium ribbon be cleaned before burning in air?
Ans :- Because of unwanted impurities are removed.
Q.2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + chloride → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + water → Sodium hydroxide + Hydrogen.
Ans :- (i) H₂+ Cl₂→ 2HCl
(ii) 3BaCl₂+ AI₂(SO₄)₃ → 3BaSO₄ + 2AICl₃
(iii) 2Na + 2H₂O → 2NaOH + H₂
Q.3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydrochloric acid solution (in water) to produce sodium chloride solution an water.
Ans :- (i) Bacl₂(aq) + Na₂SO₄(aq) → BaSO₄ (s) + 2Nacl(aq)
(ii) NaOH (aq) + Hcl(aq) → Nacl(aq) + H₂O
Page No – 10
Q.1. A solution of substance ‘x’ is used for white-washing.
(i) Name the substance ‘x’ and write its formula.
(ii) Write the reaction of the substance ‘x’ named in (i) above with water.
Ans :- (i) x’ is quick lime; CaO
(ii) CaO + H₂O → Ca(OH)₂
Q.2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Ans :- In activity 1.7 water is electrolysed to give H₂ gas at one electrode and O₂ gas at the other electrode according to the given chemical reaction.
2H₂O → 2H₂ + O₂
Thus, two molecules of water on electrolysis give two molecules of hydrogen gas and one molecule of oxygen gas or the amount of hydrogen gas collected would be double than that of oxygen gas.
Page No -13
Q.1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?
Ans :- The following chemical reaction takes place when an iron nail dipped in copper sulphate solution:
Fe(S) + CaSO₄(aq) → FeSO₄(aq) + Cu(s)
(coper sulphate) (Iron sulphate)
In this reaction iron has displaced or removed copper from copper sulphate solution.
Thus amount of copper sulphate decreases and its colour fades.
Q.2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
Ans :- When a solution of hydrochloric acid is added to a solution of lead nitrate, a white precipitate of lead chloride is formed.
Pb(NO₃)₂(aq) +2Hcl(aq) → Pbcl₂ (s) + 2HnO₃ (aq)
Q.3. Identify the substances that are oxidised and the substances that are reduced in the following reactions :
(i) 4Na(s) + O₂ (g) → 2Na₂O (s)
(ii) CuO (s) + H₂ (g) → Cu (s) + H₂O (l)
Ans :- (i) Oxidised :- Na(s), H₂(g)
(ii) Reduced :- O₂(g), CuO(s)
EXERCISES
Q.1. Which of the statements about the reaction below are incorrect?
2PbO(s)+C(s) → 2Pb(s) + (Co₂(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidized.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Ans :- (i) (a) and (b)
Q.2. Fe₂O₃+ 2Al → Al₂O₃+ 2Fe The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction .
(c) decomposition reaction.
(d) displacement reaction.
Ans :- (d) déplacement réaction.
Q.3. What happens when dilute hydrochloric acid is added to iron filling? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Ans :- (a) Hydrogen gas and iron chloride are produced.
Q.4. What is a balanced chemical equation? Why should chemical equations be balanced?
Ans :- A chemical equations is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation.
The chemical equations must be balanced because the number of atoms of each element remains the same, before and after a chemical reaction.
Q.5. Translate the following statements into chemical equations and then balance them :-
(a) Hydrogen gas combines with nitrogen to form ammonia-
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Ans :- (a) 3H₂(g) + N₂(g) → 2NH₃ (g)
(b) 2H₂s(g) + 3O₂ → 2SO₂(g) + 2H₂O(e)
(c) 3BaCl₂(aq) +Al₂(SO₄)₃(aq) → 2AlCI₃(aq)+3BaSO₄(s)
(d) 2K(s) + 2H₂O(l) – 2KOH (aq) +H₂(g)
Q.6. Balance the following chemical equations –
(a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂+H₂O
(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O
(c) Nacl + AgNO₃ → Agcl + NaNO₃
(d) Bacl₂ + H₂SO₄ → BaSo₄ + HCI
Ans :- (a) 2HNO₃ + Ca(OH)₂→ Ca(NO₃)₂ +2H₂O
(b) 2NaOH + H₂SO₄ → Na₂SO₄+2H₂O
(c) Nacl + AgNO₃ → Agcl + NaNO₃
(d) Bacl₂ + H₂SO₄ → BaSO₄+2Hcl
Q.7. Write the balanced chemical equations for the following reactions :
(a) Calcium hydroxide + Carbon dioxide → Calcium Carbonate + water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium Chloride + copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride.
Ans :- (a) Ca(OH)₂+ CO₂ → CaCO₃+ H₂O
(b) Zn+2AgNO₃ → Zn(NO₃)₂+2Ag
(c) 2Al + 3CuCl₂ → 2AICI₃+ 3Cu
(d) BaCl₂ + K₂SO₄ → BaSo₄ + 2Kcl
Q.8. Write the balanced chemical equation for the following mule and identify the type of reaction in each case.
(a) Potassium bromide (aq) + Barium iodide (ag) → Potassium iodide (aq) + Barium bromide(s)
(b) Zinc carbonate (s) → Zinc oxide(s) + carbon di-oxide(g)
(c) Hydrogen(g) + chloringe(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen (g)
Ans :- (a) 2KBr (aq) + Bal₂ (aq) – →KI(aq) + BaBr₂ (s)
Type :- Double displacement reaction.
(b) ZnCO₃(s) → ZnO(s) + CO₂(g)
Type :- Decomposition reaction.
(c) H₂(g) + Cl₂ (g) – 2HcI(g)
Type :- Combination reaction.
(d) Mg(s) + 2Hcl(aq) → Mgcl₂ (aq) + H₂(g)
Type :- Displacement reaction.
Q.9. What does one mean by exothermic and endothermic reactions? Give examples.
Ans :- Exothermic reactions :- reactions in which heat is given out along with the products are called exothermic reactions.
Examples :- (i) C(s) + O₂(g) → Co₂(g) + 393.7 kJ (∆H=-393.7 KJ)
(ii) N₂(g) + 3H₂(g) → 2NH₃ (g) + 92KJ (∆H=- 92KJ)
Endothermic reactions :- Reactions in which energy is absorbed are known as endothermic reactions.
Examples :- (i) C(s) + 2S(s) → CS₂(b) – 92 KJ (∆H=-92KJ)
(ii) N₂(g) + O₂(g) → 2NO(g) – 180.5KJ (∆H=-180.5 KJ)
Q.10. Why is respiration considered an exothermic reactions? Explain.
Ans :- During digestion, food is broken down into simpler substances. For example- rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. This reaction is known as respiration. The chemical equation is-
C₆H₁₂ O₆ (aq) + 6O₂ (aq) → 6CO₂ (aq) + 6H₂O(e) +energy Thus respiration is an exothermic reaction.
Q.11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Ans :- Decomposition reactions are opposite of combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances. For example –
In a combination reaction two or more substances combine to form a new single substance.
For example :- C(s) + O₂(g) → CO₂(g)
Q.12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Ans :-
Q.13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Ans :- When an element displaces another element from its compound, a displacement reaction occurs. In other hard two different atoms an groups of atoms are exchanged in double displacement reactions.
Equation of displacement reaction :-
Fe(s) + CuSo₄ (aq) → Cu(s) + FeSO₄ (aq)
In this reaction iron displaces copper from its solution.
Equation of double displacement reaction :-
AgNO₃ (aq) + Nacl (aq) → Agcl(s) + NaNO₃
In this reaction silver nitrate and sodium chloride exchanged cl⁻ and NO₃⁻ ions between them.
Q.14. In the refining of silver, recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Ans :- AgNO,₃ (aq) + Cu(s) → CuNO₃ (aq) + Ag (s)
Q.15. What do you mean by a precipitation reaction? Explain by giving examples.
Ans :- Any reaction that produces a precipitate can be called a precipitation reaction.
For example :-
Na₂SO₄ (aq) + Bacl₂ (aq) → BaSO₄ (s) + 2Nacl(aq)
(Sodium sulphate) (Barium chloride) (Barium sulphate) (Sodium chloride)
The white precipitate of BaSO₄ is formed by the reaction of SO₄²⁻ and Ba²⁺
Q.16. Explain the following in terms of gain or logs of oxygen with two example reach –
(a) Oxidation.
(b) Reduction.
Ans :- Oxidation :- The chemical reactions in which a substance gains oxygen is called oxidation.
Example :-
(b) Reduction :- The chemical reactions in which a substance losses oxygen is called reduction.
Example :- ZnO + C → Zn + CO
Cuo + H₂ → Cu + H₂O
Q.17. A shiny brown colured element ‘x’ on heating in air becomes black in colour. Name the element ‘x’ and black coloured compound formed.
Ans :- Element ‘x’ is copper (Cu)
Black colour compound is copper oxide (CuO)
2Cu (s) + O₂ → 2CuO
Brown fromair Black
Q.18. Why do we apply paint on iron articles?
Ans :- Paint saves iron articles from damage on iron articles.
Q.19. Oil and fat containing food items are flushed with nitrogen. Why?
Ans :- To keep food items fresh and save these from oxidising effect of oxygen, food items are flushed with nitrogen,
Q.20 . Explain the following terms with an example each:
(a) corrosion.
(b) Rancidity.
Ans :- (a) Corrosion :- When a metal is attacked by substances around it such as moisture, acids etc., it is said to corrode and this process is called corrosion.
The black coating on silver and the green coating on copper are examples of corrosion.
(b) Rancidity :- When fats and oils ar oxidised, they become rancid and their smell and taste changes and causes infection on eating. This is called Rancidity.
Chips manufactures usually flush ags of chips with gas such as nitrogen to prevent the chips from getting oxidised.
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