CBSE Class 10 Science Chapter-1 Chemical Reactions and Equations Important Questions – Free PDF Download
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CBSE Class 10 Science Chapter-1 Important Questions
CBSE Class 10 science Important Questions Chapter 1 – Chemical Reactions and Equations
3 Mark Questions
1. (a) Define Rusting
(b) Why do you apply paint an iron articles?
Ans. (a) The process of slow eating of the surface of metal iron when exposed to air for a longer period of time is called rusting.
(b) We apply paint on iron articles because it forms a protective coating on the surface of iron and we can protect it against rusting.
2. White the balanced reactions for the following
(i) Potassium Bromide (aq) + Barium iodide (aq) 
Potassium iodide (aq) + Barium Bromide(aq)
(ii) Zinc carbonate (s) Zinc oxide (s) + carbon dioxide (g)
(iii) Hydrogen (g) + chlorine (g) Hydrogen chloride
Ans. (i) 
(ii) 
(iii) 
3. The reaction is given by
(i) White the ionic equation for the reaction
(ii) The ionic equations can be represented by two half equations.
Write these equations.
(iii) Explain why this is a redox reaction
Ans. (i) 
(ii) The half ionic equations are-
(iii) The first half represents oxidation since these is loss of electrons and second half represents reduction as there is gain of electrons.
4. What are neutralization reactions? Why are they named so? Give one example?
Ans. A neutralization reaction is the chemical reaction between an acid and base dissolved in water
For 
It is called neutralization reaction because both 
and 
formed as the products, are neutral in nature.
5. Identify the type of reaction in the following
(a) ZnCO3 + 2HCl (aq) 
ZnCl2 (aq) + H2CO3 (aq)
(b) 2NaBr (aq) +Cl (g) 
2Nacl (aq) + Br2 (aq)
(c) 2CuO (S) 
2Cu (s) + O2 (g)
Ans. (a) Double decomposition reaction.
(b) Displacement reaction.
(c) Decomposition reaction.
6. A student dropped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was then passed through lime water. What change would be observed in lime water? Write balanced chemical equation for both the change observed?
Ans. When marble reacts with dil. HCl, CO2 gas evolved
CaCO3 (s) +2HCl (aq) 
CaCl2 (aq) + H2O (l) + CO2 (g)
When this gas is evolved and is passed through lime water, becomes milky due to the formation of insoluble Calcium carbonate
Ca (OH) 2 + CO2 (g) 
CaCO3 (s) +H2O (l)
But when milkiness disappears i.e. when CO2 gas is passed in excess through CaCO3 (s)
CaCO3 (s) + CO2 (g) +H2O (l) 
Ca (HCO3)2 (aq)
7. In the reaction MnO2 +4HCl 
MnCl2 + 2H2O +Cl2
(a) Name the substance oxidised.
(b) Name the oxidising agent.
(c) Name the reducing agent and the substance reduced.
Ans. (a) HCL has been oxidized to Cl2
(b) MnO2
(c) HCL is the reducing agent and Mno2 has been reduced to MnCl2
8. Give one example each of
(a) Thermal decomposition
(b) Electrolytic decomposition
(c) Photo decomposition
Ans. (a) MgCo3 (s) 
MgO (s) +Co2 (g)
(b) 2H2O (l) 
2H2 (g) +O2 (g)
(c) 2H2O2 (l) 
2H2O (l) +O2 (g)
9. Write three equations for decomposition reaction where energy is supplied in the form of heat, light and electricity?
Ans. (i) 
(ii) 
(iii) 
10. When you mix solutions of lead (II) nitrate and potassium iodide,
(i) What is the colour of the precipitate formed? Name the compound evolved?
(ii) Write a balanced chemical reaction?
(iii) Is this a double displacement reaction?
Ans. (i) The precipitate is yellow in colour and the compound is lead (II) Iodide.
(ii) 
(iii) Yes it is a double displacement reaction.
11. Transfer the following into chemical equations and balance them.
(i) Hydrogen gas combines with nitrogen to from ammonia.
(ii) Hydrogen sulphide gas burns in air to give water and sulphurdioxide.
(iii) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Ans. (i) 
(ii) 
(iii) 
12. Balance the equations
(i) 
(ii) 
(iii) 
Ans. (i) 
(ii)
(iii) 
13. A compound ‘X’ is used for drinking, has pH =7.Its acidified solution undergoes decomposition in presence of electrictiy to produce gases ‘Y’ and ‘Z’ The volume of Y is double than Z. Y is highly combustible whereas Z is supporter of combustion. Identify X, Y & Z and write the chemical reactions involved.
Ans. 
14. An aqueous solution of metal nitrate P reacts with sodium bromide solution to form yellow ppt of compound Q which is used in photography. Q on exposure to sunlight undergoes decomposition reaction to form metal present in P along with reddish brown gas. Identify P &Q. Write the chemical reaction & type of chemical reaction.
Ans. P = Ag NO
Photochemical decomposition.
15. Bhawana took a pale green substance A in a test tube. And heated it over the flame of a burner. A brown colored residue B was formed along with evolution of two gases with burning smell of sulphur. Identify A & B. Write the chemical reaction involved.
Ans. 
16. A reddish brown vessel developed a green colored solid X When left open in air for a long time. When reacted with dil 
, it forms a blue colored solution along with brisk efficient due to colourless & odourless gas Z. X decomposes to form black colored oxide Y of a reddish brown metal along with gas Z, Identify X, Y, & Z.
Ans. 
17. A student has mixed the solutions of lead (II) nitrate and potassium iodide.
(i) What was the colour of the precipitate formed? Can you name the compound?
(ii) Write the balanced chemical equation for this reaction.
(iii) What type of reaction is it?
Ans. (i) Yellow, Lead iodide
(ii) 
(iii) Double displacement reaction
18. Name the type of reaction seen in the diagram below. Write the reaction for the Same.
Ans. Displacement Reaction
Oxygen and is being oxidized.
19. A student dropped few pieces of marble in dilute HCI contained in a test tube. The gas evolved was passed through lime water. What change would be observed in lime water? Write chemical reactions for both the changes observed.
Ans.
20. Astha has been collecting silver coins and copper coins. One day she observed a black Coating on silver coins and a green coating on conner coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings?
Ans. Corrosion is responsible for this coating. Black coating is due to formation of 
And green coating is due to formation of 
21. Write the balance equation for the following reactions Give reasons for the following reactions?
i. Hydrogen + Chlorine Hydrogen chloride
ii. Barium chloride + Aluminium sulphate Barium sulphate + Aluminium chloride
iii. Sodium + water Sodium hydroxide + water
Ans. The chemical equations are as follows-
i. H2 +Cl2 2HC
ii. 3BaCl2 + Al2 (SO4)3 3BaSO4 + 2AlCl3
iii. 2Na + 2H2O 2NaOH +H2
22. 
+ 2Al 
+ 2Fe
The above reaction is an example of a
(a) combination reaction
(b) double displacement reaction
(c) decomposition reaction
(d) displacement reaction
Ans. This is an example of displacement reaction because Fe in FeO3 has been displaced by Al. Hence correct answer is (d).
23. What is balanced chemical equation? Why should chemical equation be balanced?
Ans. The reaction in which the number of atoms of each element is equal on the reactant side and product side is called balanced equation. Chemical reaction should be balanced because only a balanced equation tells us the relative quantities of different reactants and products involved in the reaction.
24. Why respiration is considered an exothermic reaction? Explain.
Ans. During respiration, we inhale oxygen from the atmosphere which reacts with glucose in your body cells to produce carbon dioxide and water.
C6H12O6 (aq) + 6O2 6CO2 (g) + 6H2O (l) + heat
Heat is liberated in this process; hence respiration is considered an exothermic reaction.