Important Questions for CBSE Class 10 Science Chapter 1: Understanding the basics of chemical reactions is essential for students. Chapter 1 focuses on balancing equations, identifying reaction types, and explaining simple chemical changes.
Practising chemical reaction and equation Class 10 important questions helps students improve accuracy and score better in exams.
This will help you include clear, well-selected, important questions of chemical reactions and equations for Class 10 to strengthen concepts and boost exam preparation efficiently.
Chemical Reactions and Equations Class 10 Important Question Answers
Here are well-selected and high-weightage questions from Chapter 1 to help you understand concepts better and prepare effectively for exams. These questions focus on reaction types, balancing equations, and key applications.
Multiple Choice Question (1 Mark)
1. Barium chloride, on reacting with ammonium sulphate, forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of 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 only
Sol. (D) ii and iv only
2. A Brown and bright element ‘X’, when heated in the presence of air turns into a black substance ‘Y’. If Hydrogen gas is passed over this heating material again, ‘X’ is obtained. Identify ‘X’ and ‘Y’.
(A) Cu and CuO
(B) S and SO2
(C) C and CO2
(D) Na and NaH
Sol. (A) Cu and CuO
3. Identify the correct oxidant and reductant in the following reaction:
PbS + 4H2O2 → PbSO4 + 4H2O
(A) PbS - Oxidant, H2O2 - Reductant
(B) PbS - Reductant, PbSO4 - Oxidant
(C) PbS - Reductant, H2O2 - Oxidant
(D) H2O2 - Oxidant, H2O – Reductant
Sol. (C) PbS - Reductant, H2O2 – Oxidant|
4. Which of the following reactions is not balanced?
(A) 2NaHCO3 → Na2CO3 + H2O + CO2
(B) 2C4H10 + 12O2 → 8CO2 + 10H2O
(C) 2Al + 6H2O → 2Al(OH)3 + 3H2
(D) 4NH3 + 5O2 → 4NO + 6H2O
Sol. (B) 2C4H10 + 12O2 → 8CO2 + 10H2O
5. Sodium reacts with water to form sodium hydroxide and hydrogen gas. The balanced equation which represents the above reaction is
(A) Na(s) + 2H2O(l) → 2NaOH(aq) + 2H2(g)
(B) 2Na(s) + 2H2O(l)→ 2NaOH(aq) + H2(g)
(C) 2Na(s) + 2H2O(l)→ NaOH(aq) + 2H2(g)
(D) 2Na(s) + H2O(l)→ 2NaOH(aq) + 2H2(g)
Sol. (B) 2Na(s) + 2H2O(l)→ 2NaOH(aq) + H2(g)
6. It is important to balance the chemical equations to satisfy the law of conservation of mass. Which of the following statements of the law is incorrect?
(A) The total mass of the elements present in the reactants is equal to the total mass of the elements present in the products.+
(B) The number of atoms of each element remains the same, before and after a chemical reaction.
(C) The chemical composition of the reactants is the same before and after the reaction.
(D) Mass can neither be created nor can it be destroyed in a chemical reaction.
Sol. (C) The chemical composition of the reactants is the same before and after the reaction.
7. Assertion (A): The Following is a balanced chemical equation for the action of steam on iron
3Fe 4H O Fe O 4H + ⎯⎯→ + 2 3 4 2
Reason (R): The law of conservation of mass holds good for a chemical equation.
(A) Both (A) and (R) are true, and reason (R) is the correct explanation of the assertion (A).
(B) Both (A) and (R) are true, but reason (R) is not the correct explanation of the assertion (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.
Sol. (A)
Both (A) and (R) are true, and reason (R) is the correct explanation of the assertion (A).
8. Which of the following reactions is not correct
(A) Zn + CuSO4 → ZnSO4 + Cu
(B) 2Ag + Cu(NO3)2 → AgNO3 + Cu
(C) Fe + CuSO4 → FeSO4 + Cu
(D) Mg + 2HCl → MgCl2 + H2
Sol. (B) 2Ag + Cu(NO3)2 → AgNO3 + Cu
9. Identify the correct statement PBO + C → Pb + CO
(A) PbO is oxidised
(B) C act as an oxidising agent
(C) C act as a reducing agent
(D) Reaction does not represent a redox reaction.
Sol. (C) C act as a reducing agent
10. A substance which oxidises itself and reduces others is known as
(A) Oxidising agent
(B) Reducing agent
(C) Both (A) and (B)
(D) None of these.
Sol. (D) Reducing agent
11. Take about 5 ml of the dilute. HCl in a test tube and add a few pieces of fine zinc granules to it. Which gas is evolved?
(A) Chlorine (B) Hydrogen
(C) HCl (D) Nitrogen
Sol. (D) Hydrogen
12. When aqueous solutions of potassium iodide and lead nitrate are mixed, an insoluble substance separates. The balanced chemical equation for the reaction involved is
(A) Kl + PbNO3 ⎯→ Pbl + KNO3
(B) 2Kl + Pb(NO3)2 ⎯→ Pbl2 + 2KNO3
(C) Kl + Pb(NO3)2 ⎯→ Pbl + KNO3
(D) Kl + PbNO3⎯→ Pbl2 + KNO3
Sol. (B) 2Kl + Pb(NO3)2 ⎯→ Pbl2 + 2KNO3
13. A metal ribbon ' X ' burns in oxygen with a dazzling white flame, forming a white ash ' Y. The correct description of X, Y and the type of reaction is
(A) X = Ca; Y = CaO Type of reaction = Decomposition
(B) X = Mg; Y = MgO Type of reaction = Combination
(C) X = Al; Y = Al2O3 Type of reaction = Thermal decomposition
(D) X = Zn; Y = ZnO; Type of reaction = Endothermic
Sol. (B) X = Mg; Y = MgO Type of reaction = Combination
14. Name the type of chemical reaction which takes place when quicklime is added to water.
Sol. Combination Reaction
15. What is a balanced chemical equation?
Sol. An equation with an equal number of atoms of each element on both sides of the equation is called a balanced chemical equation.
16. Translate the following statement into a chemical equation and then balance it:
Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate.
Sol. The chemical equation for the given chemical reaction is:
BaCl2(aq) + Al2(SO4)3(aq) → AlCl3(aq) +BaSO4(s) The balanced chemical equation is: 3 BaCl2(aq) + Al2(SO4)3(aq) → 2AlCl3(aq) + 3BaSO4(s)
17. Give the chemical name of the reactants as well as the products of the following chemical equation
2HNO Ca OH Ca(NO ) 2H O + ⎯⎯→ +
Sol. Reactant: Nitric Acid, Calcium hydroxide.
Product: Calcium Nitrate, Water.
18. What is the difference between binary fission and Multiple fission?
19. Write balanced chemical equations for the following chemical reactions:
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Lead + Copper chloride → head chloride + copper
(iii) Zinc oxide + Carbon → Zinc + Carbon monoxide
Sol.
(i) H2 + Cl2 → 2HCl
(ii) Pb + CuCl2 → PbCl2 + Cu
(iii) ZnO + C → Zn + CO
20. Classify the following reaction into different types:
(i) AgNO3(aq) + NaCl(aq) ⎯→ AgCl(s) + NaNO3(aq)
(ii) CaO(s) + H2O(l) ⎯→ Ca(OH)2(aq)
(iii) 2KClO3(s) ⎯⎯→2KCl(aq) + 3O2(g)
(iv) Zn + CuSO4 ⎯→ZnSO4 + Cu
Sol.
i. Double Displacement Reaction
ii. Combination Reaction
iii. Thermal Decomposition Reaction
iv. Displacement Reaction
21. Study the following equation of a chemical reaction:
H2 + Cl2 → 2HCl
(i) Identify the type of reaction.
(ii) Write a balanced chemical equation of another example of this type of reaction.
Sol.
i. Combination Reaction
ii. CaO + H2O → Ca(OH)2
22. State the type of chemical reactions represented by the following equation:
(i) A + BC → AC + B
(ii) A + B → C
(iii) PQ + RS → PS +RQ
Sol.
(i) Displacement reaction
(ii) Combination reaction
(iii) Double displacement reaction
23. (A) Define a double displacement reaction.
(B) Write the chemical equation of a double displacement reaction, which is also a
(i) Neutralisation reaction and
(ii) Precipitation reaction.
Sol. (A) Double displacement reactions are those in which two chemical substances react by exchanging ions between the reactions.
(B)
i. NaOH + HCl → NaCl + H2O
ii. BaCl2 + H2SO4 → BaSO4 + 2HCl
24. Mention with reason the colour changes observed when :
(i) Silver chloride is exposed to sunlight.
(ii) Copper powder is strongly heated in the presence of oxygen.
(iii) A piece of zinc is dropped in a copper sulphate solution.
Sol.
(i) When silver chloride is exposed to sunlight, photo decomposition of silver chloride takes place, which results in the formation of silver and colour changes to grey.
(ii) When the copper powder is strongly heated in the presence of oxygen, copper undergoes oxidation and black-coloured copper oxide is formed.
(iii) When a piece of zinc is dropped in copper sulphate solution, zinc displaces copper, and the solution changes from blue to colourless due to the formation of zinc sulphate.
25. A shining metal ‘M’, on burning, gives a dazzling white flame and changes to a white powder ‘N’.
(i) Identify ‘M’ and ‘N’.
(ii) Represent the above reaction in the form of a balanced chemical equation.
(iii) Does ‘M’ undergo oxidation or reduction in this reaction? Justify.
Sol..
(i) ‘M’: Magnesium, ‘N’ Magnesium oxide.
(ii) 2Mg + O2 → 2MgO
(iii) M is undergoing Oxidation, as magnesium is changing to magnesium oxide. That means oxygen is being added to magnesium. The addition of oxygen to a substance is called oxidation, so magnesium undergoes oxidation.
26. In the electrolysis of water
(i) Name the gases liberated at the anode and the cathode.
(ii) Why is it that the volume of gas collected on one electrode is two times that on the other electrode?
(iii) What would happen if dilute H2 SO4 is not added to water?
Sol..
(i) In the electrolysis of water, hydrogen is collected at the cathode and oxygen is collected at the anode.
(ii) Water is composed of 2 atoms of H and 1 atom of O. Therefore, the amount of H is double that of O. The two electrodes collect H2 and O2 separately. Therefore, the volume of gas collected in one electrode is double the volume of gas collected in the other electrode.
(iii) Pure water is a bad conductor of electricity. If dilute sulphuric acid is not added to water, it will not undergo electrolysis.
27. 1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemicalequations of reactions, the name and the colour of the products formed in each case.
Sol. When 1g of copper powder is taken into a china dish and heated, copper oxide (CuO) is formed.
2Cu (s) + O₂ (g) → 2CuO (s)
Copper + Oxygen → Copper oxide (black)
When hydrogen gas is passed over heated Copper Oxide(CuO), copper metal is obtained.
The black-coloured CuO is reduced, and brown colour Cu metal is formed.
CuO (s) + H₂ (g) → Cu (s) + H₂O (l)
Copper oxide + Hydrogen → Copper + Water
28. A compound 'A' is used in the manufacture of cement. When dissolved in water, it evolves a large amount of heat and forms compound ' B'.
(i) Identify A and B.
(ii) Write a chemical equation for the reaction of A with water.
(iii) List two types of reaction in which this reaction may be classified.
Sol.
(i) A = Calcium Oxide (CaO) B = Calcium hydroxide (Ca(OH)2)
(ii) CaO H O Ca(OH) + → 2 2.
(iii) Combination reaction and Exothermic Reaction.
29. Identify the type of each of the following reactions. Also, write a balanced chemical equation for each reaction.
(i) A reaction in which the reaction mixture becomes warm.
(ii) A reaction in which an insoluble substance is formed.
Sol.. (i) Exothermic reaction CaO + H2O ⎯→ Ca(OH)2 + Heat
(ii) Precipitation reaction BaCl2(aq) + MgSO4(aq) → BaSO4(s) + MgCl2(aq)
30. Lead nitrate solution is added to a test tube containing potassium iodide solution.
(i) Write the name and colour of the compound precipitated.
(ii) Write the balanced chemical equation for the reaction involved.
(iii) Name the type of reaction.
Sol.
(i) The name of the compound precipitated is Lead iodide. It is yellow in colour.
(ii) The balanced chemical equation for the reaction involved is given below:
P I b NO 2K aq + → + I aq bP 2KNO s aq
(iii) It is a Double displacement reaction and a precipitation reaction.
31. Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions.
(i) Zinc reacts with silver nitrate to produce zinc nitrate and silver.
(ii) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.
Sol.. (i) Displacement reaction
Zinc Silver nitrate Silver Zinc nitrate
Zn (s) + 2AgNO₃ (aq) → Zn(NO₃)₂ (aq) + 2Ag (s)
Zinc + Silver nitrate → Zinc nitrate + Silver
(ii) Double displacement reaction
Pb(NO₃)₂ (aq) + 2KI (aq) → PbI₂ (s) + 2KNO₃ (aq)
Lead nitrate + Potassium iodide → Lead iodide + Potassium nitrate
32. Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity.
Sol.
Decomposition where heat is supplied:
ZnCO₃ —(Heat)→ ZnO + CO₂
Zinc carbonate → Zinc oxide + Carbon dioxide
Decomposition where electricity is supplied:
2H₂O (l) —(Electricity)→ 2H₂ (g) + O₂ (g)
Decomposition of silver chloride in the presence of sunlight:
2AgCl —(Sunlight)→ 2Ag + Cl₂
33. (i) In the following reaction _ MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
Identify the oxidant and reductant.
(ii) Give reasons:
(a) Antioxidants are added to foods containing fats and oils.
(b) White silver chloride turns grey in sunlight.
Sol.
(i) Oxidant: MnO2, Reductant: HCl
(ii) (a) Antioxidants are added to food to prevent the oxidation of fats and oils and thus increase the shelf life of food.
(b) White silver chloride turns grey in sunlight due to the decomposition of silver chloride into silver and chlorine by light.
sunlight 2AgCl 2Ag Cl ⎯⎯⎯→ + 2
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