CBSE 10th Chemistry | Chemical Reactions and Equations -NCERT Questions with Answers

Chemical Reactions and Equations -NCERT Questions with Answers

Question 1. Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) clip_image0022Pb(s) + CO2(g)

(a) Lead is getting reduced,

(b) Carbon,dioxide is getting oxidised.

(c) Carbon is getting oxidised.

(d) Lead oxide is getting reduced

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

Answer.

The statements (a) and (b) are incorrect because PbO is getting reduced, not Pb, similarly C is getting oxidized not CO2.

Question 2. Fe2O3 + 2Al clip_image002[1]Al2O3 + 2Fe

The above reaction is an example of a

(a) combination reaction

(b) double displacement reaction

(c) decomposition reaction,

(d) displacement reaction.

 

Answer.

(d) The given reaction is an example of displacement reaction as in this reaction Al displaces, Fe from Fe2O3.

Question 3. What happens when dilute hydrochloric acid is added to iron fillings? 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

 

Answer.

(a) Fe(s) + 2HCl(aq) clip_image002[2] FeCI2(aq) + H2(g)

Question 4. What is a balanced chemical equation? Why should chemical equations be balanced?

Answer.

Balanced chemical equation: – A chemical equation is said to be balanced if the number of atoms of each element participating in the reaction are equal on both side of the equation.

The chemical reaction should be balanced because law of conservation of mass holds good which states that “in a chemical reaction total mass of the reactant must be equal to the total mass of the product”.

Quiestion 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.

Answer.

(a) N2(g) + 3H2(g) clip_image002[3]2NH3(g)

(b) 2H2S(g) +3O2(g) clip_image002[4]2H2O(l) +2SO2(g)

(c) 3BaCl2(aq) + Al2 (SO4)3(s)clip_image002[5] 3BaSO4(s) + 2AlCl3(aq)

(d) 2K(s) + 2H2O(l) clip_image002[6] 2KOH(aq)+H2(g)

Question 6. Balance the following chemical equations.

(a) 2HNO3 + Ca(OH)2 clip_image002[7] Ca(NO3)2 + H2O

(b) NaOH + H2SO4 clip_image002[8] Na2SO4 + H2O

(c) AgNO3 + NaCl clip_image002[9]AgCl + NaNO3.

(d) BaCl2 + H2SO4 clip_image002[10]BaSO4 + HCl

Answer.

(a) 2HNO3 + Ca(OH)2 clip_image002[11] Ca(NO3)2 + 2H2O

(b) 2NaOH + H2SO4 clip_image002[12] Na2SO4 + 2H2O

(c) AgNO3 + NaCl clip_image002[13] AgCl + NaNO3

(d) BaCl2 + H2SO4 clip_image002[14]BaSO4 + 2HCl

Question 7. Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxideclip_image002[15] Calcium carbonate + water

(b) Zinc + Silver nitrate clip_image002[16] Zinc nitrate + Silver

(c) Aluminium + Copper chloride clip_image002[17] Aluminium chloride + Copper

(d) Barium chloride + Potassium sulphate clip_image002[18]Barium sulphate + Potassium chloride

Answer.

(a) Ca(OH)2 + CO2 clip_image002[19] CaCO3 + H2O

(b) Zn+2AgNO3clip_image002[20] Zn(NO3)2 + 2Ag

(c) 2Al + 3CuCl2 clip_image002[21]2AlCl3 + 3Cu

(d) BaCl2 + K2SO4clip_image002[22] BaSO4+2KCl

Question 8. Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + Barium iodide(aq) clip_image002[23] Potassium iodide(aq) + Barium bromide(aq)

(b) Zinc carbonate(s) clip_image002[24] Zinc oxide(s) + Carbon dioxide(g)

(c) hydrogen(g) + Chlorine(g) clip_image002[25] Hydrogen chloride(g)

(d) Magnesium(s) + Hydrochloric acid(aq) clip_image002[26] Magnesium chloride(aq) + Hydrogen(g)

Answer.

(a) 2KBr(aq) + Bal2(aq) clip_image002[27] 2KI(aq) + BaBr2(aq)

(b) ZnC03(s) clip_image002[28] ZnO(s) + CO2(g)

(c) H2(g) + Cl2(g) clip_image002[29] 2HCl(g)

(d) Mg(s) + 2HCl(aq) clip_image002[30] MgCl2(aq) + H2(g)

Question 9. What does one mean by exothermic and endothermic reaction? Give examples.

Answer.

Exothermic reaction: – Those reactions which occur with evolution of heat are exothermic reactions. e.g.

2NaOH(aq) + H2SO4(aq) clip_image013Na2SO4(aq) + 2H2O(l) + Q

Enothermic reaction: – Those reactions which require heat to occur are endothermic reactions, e.g.

2Pb(NO3)2(s) + Q clip_image002[31] 2PbO(s) + 4NO2(g) + O2(g)

Question 10. Why is respiration considered an exothermic reaction? Explain.

Answer.

During respiration oxidation of glucose occur which produce heat energy.

Question 11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Answer.

During decomposition reaction a single reactant decompose to form two or more products, whereas in combination two or more reactant react to form a single product, e.g.

N2 + 3H2 clip_image002[32]2NH3 (Combination reaction.)

2H2O image 2H2 + O2 (Decomposition reaction.)

Question 12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Answer.

image

 

Question 13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Answer.

Displacement reaction: In this reaction an element which is more active displaces the other element which is less active from its salt solution.

e.g. Fe(s) + CuSO4(aq) clip_image002[33] FeSO4(aq) + Cu(s)

Double displacement reaction: In this reaction exchange of ions between two reactants take place, e.g.

BaCl2(aq) + Na2SO4(aq) clip_image002[34] BaSO4(s) + 2NaCl(aq)

Question 14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Answer.

Cu(s) + 2AgNO3(aq) clip_image002[35] Cu(NO3)2(aq) + 2Ag(s)

Question 15. What do you mean by a precipitation reaction? Explain by giving examples.

Answer.

Those reactions which produce an isoluble product or precipitate are known as precipitation reaction. e.g.AgNO3(aq) + NaCl(aq) clip_image002[36] AgCl(s) +NaNO3(aq)

Question 16. Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation

(b) Reduction

Answer.

Oxidation: Oxidation involve addition of oxygen e.g.

C + O2 clip_image002[37] CO2, C is oxidised to CO2.

N2 + O2 clip_image002[38] 2NO, N2 is oxidised to NO.

Reduction: Reduction involve removal of oxygen, e.g.

C + H2O clip_image002[39] CO + H2, H2O is reduced to H2.

CuO + H2 clip_image002[40] Cu + H2O, CuO is reduced to Cu.

Question 17. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Answer.

image

Question 18. Why do we apply paint on iron articles?

Answer.

To prevent iron articles from rusting, we apply paint on it, by which iron does not come in contact with air and moisture which cause rusting.

Question 19. Oil and fat containing food items are flushed with nitrogen. Why?

Answer.

When the oil and fat containing food is surrounded by unreactive gas nitrogen, there is no oxygen to cause its oxidation and make it rancid.

Question 20. Explain the following terms with one example each.

(a) Corrosion

(b) Rancidity

 

Answer.

Corrosion: It is a process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface.

Rancidity: When fats and oil containing food are oxidised with air or oxygen, their smells and tastes changes. This process is called rancidity.

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CBSE 10th Chemistry | Chemical Reactions -NCERT Questions with Answers

Chemical Reactions -NCERT Questions with Answers

Question 1. Why should a magnesium ribbon be cleaned before burning in air?

Answer.

The magnesium ribbon which we use has a coating of “basic magnesium carbonate” on its surface, which is formed by a slow action of moist air on it. Therefore before burning it in air, it is cleaned by a sand paper which remove the protective layer of basic magnesium carbonate from the surface of magnesium ribbon, so that it can easily burn.

Question 2. Write the balanced equation for the following chemical reactions

(i) Hydrogen + Chlorine clip_image002[108] Hydrogen chloride

(ii) Barium chloride + Aluminium sulphate clip_image002[109] Barium sulphate + Aluminium chloride

(iii) Sodium + Water clip_image002[110]Sodium hydroxide + Hydrogen

 

Answer.

(i) H2(g) + Cl2(g) clip_image002[111] 2HCl(g)

(ii) 3BaCl2(s) +Al 2(S04)3(aq) clip_image002[112] 3BaSO4{s) + 2AlCl3(aq)

(iii) 2Na(s) + 2H2O(l) clip_image002[113] 2NaOH(aq) + H2(g)

Question 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 hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

 

Answer.

(i) BaCl2(aq) + Na2SO4(aq) clip_image002[114] BaSO4(s) + 2NaCl(aq)

(ii) NaOH(aq) + HCl(aq) clip_image002[115] NaCl(aq) + H2O(aq)

Question 4. A solution of a 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,

 

Answer.

(i) Quick lime-CaO

(ii) CaO(s) + H2 O(l) clip_image002[116]Ca(OH)2(aq)

Question 5. Why is the amount of gas collected in one of the test tube in activity 1.7 (Refer NCERT) double of the amount collected in the other? Name this gas.

 

Answer.

The gases formed at two electrodes are produced due to decomposition of water on passing electricity. Since the electrolysis of water produces 2 volume of hydrogen gas and 1 volume of oxygen gas, thus we can say that the ratio of hydrogen and oxygen in water is 2:1 by volume and hence the amount of gas collected in one test tube will be double of the amount collected in other.

Question 6. Why does the colour of copper sulphate solution changes when an iron nail is dipped in it?

Answer.

As iron is more reactive than copper thus it displaces copper from copper sulphate solution.

Fe(s) +CuSO4(aq) clip_image002[117]FeSO4(aq) + Cu(s)

                               (Blue)                 (Green)

In this way concentration of copper sulphate decreases while concentration of ferrous sulphate increases. As a result colour changes from blue to green.

Question 7. Give an example of a double displacement reaction other than the one given in Activity 1.10 (Refer NCERT).

 

Answer.

image

Question 8. Identify the substances that are oxidised and the substances that are reduced in the following reactions.

(i) 4Na(s) + O2(g) clip_image002[119] 2Na2O(s)

(ii) CuO(s) + H2(g) clip_image002[120]Cu(s) + H2O(l)

 

Ans. (i)

image

 

Answer (ii)

image

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