Class 10 Science: Chemical Reactions and Equations important questions

Chemical Reactions and Equations is a chapter of Class 10 Science for the CBSE. These 13 questions are marked Very Important, Important or Practice, and each answer has been checked by our team. Use them to revise, not as a prediction of what will come in the exam.

1. Practice · 1 marks

   1. In the redox reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 (a) MnO2 is reduced to MnCl2& HCl is oxidized to H2O (b) MnO2 is reduced to MnCl2& HCl is oxidized to Cl2 (c) MnO2 is oxidized to MnCl2 & HCl is reduced to Cl2 (d) MnO2 is oxidized to MnCl2 & HCl is reduced to H2O

   (b) MnO2 is reduced to MnCl2 & HCl is oxidized to Cl2

2. Practice · 1 marks

   2. Assertion: Silver bromide decomposition is used in black and white photography. Reason: Light provides energy for this exothermic reaction.

   (c) A is true but R is false

3. Practice · 1 marks

   3. Assertion: Rusting of Iron is endothermic in nature. Reason: As the reaction is slow, the release of heat is barely evident.

   d) Assertion is false but Reason is true

4. Important · 2 marks

   4. Dil. HCl is added to Zn granules.” How will you prove that chemical change has taken place here? Support your response with two arguments.

   Response with any of the given two arguments. - Bubbles of gas/ Evolution of gas - Change in colour (Zn - silvery grey to black) - Change in temperature

5. Practice · 1 marks

   5. Identify ‘p’, ‘q’ and ‘r’ in the following balanced reaction Heat p Pb (NO3)2(s) ------> q PbO(s) + r NO2(g) + O2(g) A. 2,2,4 B. 2,4,2 C. 2,4,4 D. 4,2,2

   A. 2,2,4

6. Practice · 1 marks

   6. When 50g of lead powder is added to 300 ml of blue copper sulphate solution, after a few hours, the solution becomes colourless. This is an example of A. Combination reaction B. Decomposition reaction C. Displacement reaction D. Double displacement reaction

   C. Displacement reaction

7. Practice · 1 marks

   7. Which of the following is an endothermic reaction? A. Burning of candle. B. Cooking of food. C. Decomposition of Vegetable matter. D. Reaction of Sodium with air

   B. Cooking of food

8. Important · 2 marks

   8. Identify the type of each of the following reactions stating the reason for your answers. A. Fe2O3 + 2Al → Al2O3 + 2Fe + heat B. Pb (NO3)2 + 2KI → PbI2( )+ 2KNO3

   A. Exothermic Displacement reaction/Redox reaction. Heat is evolved or a More reactive element displaces a less reactive element or aluminium reduces iron (II) oxide to iron B. Double displacement / Precipitation reaction As there is an exchange of ions between reactants and products / (Yellow) precipitate (of Lead iodide) is formed

9. Practice · 1 marks

   9. Which of the following equations represent redox reactions and what are the values for ‘p’ and ‘q’ in these equations? Equation 1: Fe2O3(s) + 2Al(s) Al2O3 (s) + p Fe(l) + heat Equation 2: 2C4H10(g) + 13O2(g) △ 8CO2(g)+ q H2O(g) A. Only equation 1 is a redox reaction, p =1 and q=3 B. Both equations 1 and 2 are redox reactions, p= 2 and q=4 C. Only equation 2 is a redox reaction, p= 2 and q= 10 D. Both equations 1 and 2 are redox reactions, p= 2 and q=10

   D. Both equations 1 and 2 are redox reactions, p= 2 and q=10

10. Practice · 1 marks

    10. In the reaction of aqueous solution of barium chloride with aqueous solution of sodium sulphate, the aqueous solution formed will be: A. BaCl2 B. BaSO4 C. Na2SO4 D. NaCl

    D. NaCl

11. Important · 3 marks

    11. Identify the type of reaction: A. ZnO + C Zn + CO B. ZnCO3 heat ZnO + CO2 C. 2Mg + O2 2 MgO + heat

    A. Redox reaction B. Decomposition reaction and endothermic reaction C. Combination reaction and exothermic reaction

12. Practice · 1 marks

    12. In the food industry nitrogen is used as a/an A. preservative. B. oxidising agent. C. antioxidant. D. colouring agent.

    C. antioxidant

13. Very Important · 5 marks

    13. A. I. Refer to the dialogue between Alisha, Drishti and Bhushan in the chemistry lab. They are discussing rusting of iron and formation of ammonia gas. Who all do you agree with and why? Alisha: The formation of ammonia by reaction of nitrogen with hydrogen is a reduction reaction. Dristhti: Both rusting of iron and formation of ammonia are redox reactions. Bhushan: Rusting of iron is an oxidation reaction. II. Assess the following chemical equations. Identify the error(s) and rewrite the equation after correction. (i) MgCl2 + AgNO3 → AgCl2 + MgNO3 (ii) Al + H2SO4 → Al2SO4 + H2O OR B. I. Refer to the dialogue between Daljeet and Avik in the chemistry lab. They have learnt about decomposition reactions. Who has understood decomposition reactions correctly? Justify your answer. Daljeet: During a decomposition reaction, a substance decomposes to give two simpler compounds. MgCO3 decomposes on heating to magnesium oxide and carbon dioxide. Avik: No, during a decomposition reaction, a substance decomposes to give two elements. Water on electrolysis gives hydrogen and oxygen, both are elements. II. Analyse the observations given in following two cases. Are these observations correct? Give reasons to support your answer. (i) Iron fillings are added to an aqueous solution of magnesium sulphate. Observation: The colourless solution turns greenish due to formation of iron sulphate. (ii) Aluminium metal is added to dilute sulphuric acid Observation: Brisk effervescence are seen due to evolution of a gas.

    A. I. Drishti.(Alisha and Bhushan are partially correct) Oxidation and reduction go hand in hand. In case of formation of ammonia, nitrogen is getting reduced and hydrogen is oxidised. In case of rusting of iron, iron is getting oxidised while oxygen gets reduced. II. (i) MgCl2 + 2AgNO3 → 2AgCl + Mg(NO3)2 (ii) 2Al + 3H2SO4 → Al2(SO4)3 + 3H2 OR B. I. Both have understood decomposition partially. Decomposition reaction is when a single substance breaks down into simpler substances. The single substance undergoing decomposition has to be a compound while the products formed can be either elements or compounds. MgCO3 decomposes on heating to magnesium oxide and carbon dioxide even when both products formed are compounds, it is decomposition. Water on electrolysis gives hydrogen and oxygen both are elements. It is also a decomposition reaction. II. (i) Incorrect observation, iron is less reactive than Mg so it cannot displace magnesium. (ii) Hydrogen gas is formed, which produces few bubbles. Brisk effervescence is formed when carbon dioxide is formed.