CBSE Class 10 Science Chemical reactions and equations Sure Shot Questions B

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CHEMICAL REACTIONS AND EQUATIONS

Question. Why should a magnesium ribbon be cleaned before burning in air ?
Answer : To remove the layer of MgO.

Question. We need to balance a chemical equation. Give reason to justify the statement.
Answer : To obey law of conservation of mass.

Question. What is observed when a solution of potassium iodide solution is added to a solution of lead nitrate? Name the type of reaction. Write a balanced chemical equation to represent the above chemical reaction.
Answer : Yellow precipitate is formed. It is precipitation reaction.

Question. Which products will be obtained when lead nitrate is heated simply? Write balanced chemical equation for the reaction.
Answer : 

Question. Why does the color of copper sulphate solution change when an iron nail is dipped in it?
Answer : It is because displacement reaction takes place.

Question. In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?
Answer : It is because water contains hydrogen and oxygen in the ratio of 2 : 1.

Question. Name the reducing agent in the following reaction:
3MnO₂ + 4Al → 3Mn + 2Al₂O₃
Answer : Al’ is reducing agent.

Question. Giving an example list two information which make a chemical equation more useful (informative).
Answer : (i) Physical state of reactants must be mentioned
(ii) Condition in which reaction takes place are written on the arrow head

Question. What does one mean by exothermic and endothermic reactions ? Give examples.
Answer : Exothermic reactions : heat is evolved
Example : (i) C (s) + O₂ (g) → CO₂ (g) + Heat
(ii) N₂ (g) + 3H₂ (g) → 2NH₃ (g) + Heat
Endothermic reactions : heat is absorbed
Examples :(i) C (s) + 2S (s) → CS₂ (l) – Heat
(ii) N₂ (g) + O₂ (g) → 2NO(g) – Heat

Question. Name the type of chemical reaction represented by the following equation:

Answer : (i) Combination reaction
(ii) Double displacement reaction (Precipitation reaction)
(iii) Thermal Decomposition reaction.

Question. Ferrous sulphate crystals are heated in a dry boiling tube.
(i) List any two observations.
(ii) Name the type of chemical reaction taking place.
(iii) ‘Write the chemical equation for the reaction.
Answer : (i)Two observations are
(a) change in colour (b) Smell of burning sulphur
(ii) Decomposition reaction

Question. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer : In decomposition reaction, a compound is broken down into simpler compounds or elements, e.g.

Combination reaction is a reaction in which two or more elements or compounds combine to form a new compound, e.g.
N₂ (g) + 3H₂ → 2NH₃ (g)
Thus, decomposition and combination reactions are opposite to each other.

Question. The following diagram displays a chemical reaction. Observe carefully and answer the following questions

(a) Identify the type of chemical reaction that will take place and define it.
(b) How will the color of the salt change? Write the chemical equation of the reaction that takes place.
(c) Mention one commercial use of this salt.
Answer : (a) Photochemical decomposition reaction.
(b) The colour of salt will change from white to grey.
(c) in photography

Question. What is rancidity? Mention any two ways by which rancidity can be prevented.
Answer : Spoilage of food containing oil.
Prevention from rancidity:-
(i) Antioxidants
(ii) airtight container in refrigerator.

Question. A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.
Answer : ‘X’ is calcium oxide (CaO).

Question. (a) Why is respiration considered as an exothermic reaction?
(b) Identify the substance that is oxidized and reduced in the following reaction.
CaO(s) + Zn(s)→Cu(s) + ZnO(s)
Answer : (a) It is because heat is evolved during respiration.
(b) Zn is getting oxidised, CuO is getting reduced.

Question. Complete the missing components/variables given as x and y in the following reactions :

Answer : 

1. What is a balanced chemical equation? Why should chemical equations be balanced?

2. Balance the following chemical equations.

a) NaOH + H₂SO₄ → Na₂SO₄ + H₂O

b) Hg (NO₃)₂ + KI → Hg I₂ + KNO₃

c) H₂ + O₂ → H₂O

d) KClO₃ → KCl + O₂

e) C₃H₈ + O₂ → CO₂ + H₂O

3. Write the balanced chemical equations for the following reactions.

a) Zinc + Silver nitrate → Zinc nitrate + Silver.

b) Aluminum + copper chloride → Aluminum chloride + Copper.

c) Hydrogen + Chlorine. → Hydrogen chloride.

d) Ammonium nitrate → Nitrogen + Carbon dioxide + water.

4. Write the balanced chemical equation for the following and indentify the type of reaction in each case.

a) Calcium hydroxide _(aq) + Nitric acid _(aq) → Water _(l) + Calcium nitrate _(aq)

b) Magnesium _(s) + Iodine _(g) → Magnesium Iodide. _(s)

c) Magnesium_(s) + Hydrochloric acid_(aq) → Magnesium chloride_(aq) + Hydrogen_(g)

d) Zinc_(s) + Calcium chloride _(aq) → Zinc Chloride _(aq) + Ca_(s)

5. Fe₂O₃ + 2Al → Al₂O₃ + 2 Fe.

The above reaction is an example of:

a) Combination reaction b) Decomposition reaction

c) Displacement reaction d) Double decomposition reaction

6. What happens when dil.hydrochloric acid is added to iron filings? Chose 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.

7. Write an equation for decomposition reaction where energy is supplied in the form of heat/ light/ electricity.

8. What do you mean by precipitation reaction?

9. Why is respiration considered as an exothermic reaction? Explain.

10. What is the difference between displacement and double displacement reactions? Write equations for these reactions?

11. What is the use of keeping food in air tight containers?

12. What do you mean by corrosion? How can you prevent it?

13. MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 In the above equation, name the compound which is oxidized and which is reduced?

14. Match the following:

1) 2AgNO₃ + Na₂CrO₄ → Ag₂CrO₄+ 2NaNO₃ ( ) a) combination reactions

2) 2 NH₃ → N₂+ 3H₂ ( ) b) decomposition reactions

3) C₂H₄ + H₂O → C₂H₆O ( ) c) displacement reactions

4) Fe₂O₃ + 3CO → 2 F₂+ 3CO₂ ( ) d) double displacement Reactions

15. Give two examples for oxidation-reduction reaction.

16. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write the reaction involved.

17. Explain rancidity.

18. Name the reactions taking place in the presence of sunlight?

19. 2 PbO(s) + C (s) → 2Pb(s) + CO₂ (g) Which of the following statements are correct for the above?

a) Lead is reduced. b) Carbon dioxide is oxidized.

c) Carbon is oxidized. d) Lead oxide is reduced.
i) (a)and (b)

ii) (a) and (c)

iii) (a), (b), and (c) d) all.

20. Balance the following chemical equations including the physical states.

a) C₆H₁₂O₆ → C₂H₅OH + CO₂

b) Fe + O₂ → Fe₂O₃

c) NH₃ + Cl₂ → N₂H₄+NH₄cl

d) Na + H₂O → NaOH +H₂

21. Balance the chemical equation by including the physical states of the substances for the following reactions.

a) Barium chloride and sodium sulphate aqueous solutions react to give insoluble Barium sulphate and aqueous solution of sodium chloride.

b) Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride and water.

c) Zinc pieces react with dilute hydrochloric acid to liberate hydrogen gas and forms zinc chloride

22. Which of the following is not a physical change?

(a) Boiling of water to give water vapour

(b) Melting of ice to give water

(c) Dissolution of salt in water

(d) Combustion of Liquefied Petroleum Gas (LPG)

23. The following reaction is an example of a 4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g)

(i) displacement reaction

(ii) combination reaction

(iii) redox reaction

(iv) neutralisation reaction

(a) (i) and (iv)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (iii) and (iv)

24. Which of the following statements about the given reaction are correct?

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

(i) Iron metal is getting oxidised

(ii) Water is getting reduced

(iii) Water is acting as reducing agent

(iv) Water is acting as oxidising agent

(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)

25. Which of the following are exothermic processes?

(i) Reaction of water with quick lime

(ii) Dilution of an acid

(iii) Evaporation of water

(iv) Sublimation of camphor (crystals)

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (i) and (iv)

(d) (iii) and (iv)

26. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct?

(i) In beakers A and B, exothermic process has occurred.

(ii) In beakers A and B, endothermic process has occurred.

(iii) In beaker C exothermic process has occurred.

(iv) In beaker C endothermic process has occurred.

(a) (i) only
(b) (ii) only
(c) (i) and (iv)
(d) (ii) and (iii)

27. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears.
Which of the following is the correct explanation for the observation?

(a) KMnO4 is an oxidising agent, it oxidises FeSO₄

(b) FeSO4 acts as an oxidising agent and oxidises KMnO₄

(c) The colour disappears due to dilution; no reaction is involved

(d) KMnO4 is an unstable compound and decomposes in presence of FeSO4 to a colourless compound.

28. Which among the following is(are) double displacement reaction(s)?

(i) Pb + CuCl2 → PbCl2 + Cu

(ii) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

(iii) C + O₂ → CO₂

(iv) CH₄ + 2O₂ → CO₂ + 2H₂O

(a) (i) and (iv)

(b) (ii) only

(c) (i) and (ii)

(d) (iii) and (iv)

29. Which among the following statement(s) is(are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to

(i) the formation of silver by decomposition of silver chloride

(ii) sublimation of silver chloride

(iii) decomposition of chlorine gas from silver chloride

(iv) oxidation of silver chloride

(a) (i) only

(b) (i) and (iii)

(c) (ii) and (iii)

(d) (iv) only

30. Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?

(i) It is an endothermic reaction

(ii) It is an exothermic reaction

(iii) The pH of the resulting solution will be more than seven

(iv) The pH of the resulting solution will be less than seven

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (i) and (iv)

(d) (iii) and (iv)

31. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?

(i) Displacement reaction

(ii) Precipitation reaction

(iii) Combination reaction

(iv) Double displacement reaction

(a) (i) only

(b) (ii) only

(c) (iv) only

(d) (ii) and (iv)

32. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is

(a) 1:1

(b) 2:1

(c) 4:1

(d) 1:2

33. Which of the following is(are) an endothermic process(es)?

(i) Dilution of sulphuric acid

(ii) Sublimation of dry ice

(iii) Condensation of water vapours

(iv) Evaporation of water

(a) (i) and (iii)

(b) (ii) only

(c) (iii) only

(d) (ii) and (iv)

34. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?

(a) Lead sulphate (insoluble)

(b) Lead acetate

(c) Ammonium nitrate

(d) Potassium sulphate

35. Which of the following gases can be used for storage of fresh sample of an oil for a long time?

(a) Carbon dioxide or oxygen

(b) Nitrogen or oxygen

(c) Carbon dioxide or helium

(d) Helium or nitrogen

36. The following reaction is used for the preparation of oxygen gas in the laboratory Which of the following statement(s) is(are) correct about the reaction?

(a) It is a decomposition reaction and endothermic in nature

(b) It is a combination reaction

(c) It is a decomposition reaction and accompanied by release of heat

(d) It is a photochemical decomposition reaction and exothermic in nature

37. Which one of the following processes involve chemical reactions?

(a) Storing of oxygen gas under pressure in a gas cylinder

(b) Liquefaction of air

(c) Keeping petrol in a china dish in the open

(d) Heating copper wire in presence of air at high temperature

38. In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?

(a) 2H₂(l) + O₂(l) → 2H₂O(g)

(b) 2H₂(g) + O₂(l) → 2H₂O(l)

(c) 2H₂(g) + O₂(g) → 2H₂O(l)

(d) 2H₂(g) + O₂(g) → 2H₂O(g)

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