Class 10 Chemical Reactions and Equations Previous Years Questions : Solutions

Previous Years Questions Notes Important Questions

Chemical Reactions and Equations Previous Years Questions : Solutions

1. Strong heating of ferrous sulphate leads to the formation of a brown solid and two gases. This reaction can be categorised as:-
   a. displacement and redox
   b. decomposition and redox
   c. displacement and endothermic
   d. decomposition and exothermic [1 mark] [CBSE 2020]
   Sol:
   (b) decomposition and redox.
   
2. What is observed after about 1 hour of adding the strips of copper and aluminium separately to ferrous sulphate solution filled in two beakers? Name the reaction if any change in colour is noticed. Also,write chemical equation for the reaction. [2 marks] [CBSE 2019]
   Sol:
   * When we add the strips of copper to ferrous sulphate solution, there is no change in colour because copper is less reactive than iron. so, it can’t displace iron from its salt.
   Cu (s) + FeSO₄ → No change will be appear.
   * When we add the strips of aluminium to ferrous sulphate solution, there is aluminium displaces iron from its salt solution because aluminium is high reactive than iron.
   2Al (S) + 3FeSO₄ (aq) → Al₂(SO₄)₃ + 3Fe (S)
   Here, Displacement reaction will takes place.
   
3. A student wants to study a decomposition reaction by taking ferrous sulphate crystals. Write two precautions he must observe while performing the experiment. [2 marks] [CBSE 2019]
   Sol:
   Two precautions he must observe while performing this experiment are following :
   (1) Do not point the mouth of the boiling tube at your neighbours or yourself.
   (2) Test tube holder must be used while heating the test tube.
   
4. A student has set up an apparatus to show that “CO₂” is released during respiration”. After about 1 hour he observes no change in the water level in the delivery tube. write two possible reasons for the failure of the experiment. [2 marks] [CBSE 2019]
   Sol:
   
5. What is observed when a solution of sodium sulphate is added to a solution of barium chloride taken in a test tube ? Write equation for the chemical reaction involved & name the type of reaction in this case. [2 marks] [CBSE 2018]
   Sol:
   When a solution of sodium sulphate is added to solution of barium chloride, the following reaction takes place :
   BaCl₂ ​ + Na₂SO₄ ​→ 2NaCl + BaSO₄
   Here, Double displacement reaction will takes place.
   
6. A shining metal ‘M’ on burning gives a dazzling white flame & changes to a white powder ‘N’.
   1. Identify ‘M’ & ‘N’.
   2. Represent the above reaction in the form of a balanced chemical equation .
   3. Does ‘M’ undergo oxidation or reduction in this reaction ? Justify. [3 marks] [CBSE 2020]
      Sol:
      (1) M is Magnesium (Mg)
      and, N is Magnesium oxide
      Magnesium reacts with oxygen present in air and give Magnesium oxide i.e., white powder on burning.
      (2) 2Mg (S) + O₂ (g) → 2MgO (S)
      (3) (M) Magnesium undergo oxidation because oxygen is added to it.
      
7. In the electrolysis of water,
   1. Name the gases liberated at anode & cathode.
   2. Why is it that the volume of gas collected on one electrode is two times that on the other electrode?
   3. What would happen if dilute H₂SO₄ is not added to water? [3 marks] [CBSE 2020]
      Sol:
      (1) Gas liberated at Anode is Oxygen.
      and, Gas liberated at cathode is Hydrogen.
      (2) The amount of hydrogen gas collected at cathode is double the amount of oxygen gas collected at anode because when 2 mole of water is decomposed then, 2 mole of hydrogen gas and 1 mole of oxygen gas is produced.
      (3) It only increases the speed of the reaction. Hence, if we do not add sulphuric acid to water at the time of electrolysis, the conductivity will decrease and the process becomes slow.
      
8. 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 reaction where energy is supplied in the form of heat, light and electricity. [3 marks] [CBSE 2018]
   Sol:
   Thermal Decomposition : Where energy is supplied in the form of Heat.
   CaCO₃ (S) → CaO (S) + CO₂ (g)
   Photo Decompositon : Where energy is supplied in the form of light.
   2AgCl (S) → 2Ag (S) + Cl₂ (g)
   Electrolytic Decomposition : Where energy is supplied in the form of electricity.
   2H₂O (l) → 2H₂ (g) + O₂ (g)
   
9. 1. What is a double displacement reaction? Explain with an example.
   2. A small amount of quick lime is added to water in a beaker.
      1. Name and define the type of reaction that has taken place.
      2. Write balanced chemical equation for the above reaction and the chemical name of the product formed.
      3. List two main observations of this reaction. [3 marks] [CBSE 2019]
         Sol:
         (1) The reaction in which there is an exchange of ions between the reactants is called double displacement reaction.
         Ex:
         Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
         (2) (i) Combination Reaction : The reaction in which two or more substances combine to form a single product is known as combination reaction.
         (ii) CaO + H₂O → Ca(OH)₂ + Heat
         The chemical name of CaO is Quick lime.
         The chemical name of Ca(OH)₂ is Slaked lime.
         (3) (i) It is an exothermic reaction.
         (ii) The product form is Slaked lime.
         
10. .
    1. Design an activity to demonstrate the decomposition reaction of lead nitrate.
    2. Draw labelled diagram of the experimental setup. List two main observations.
    3. Write balanced chemical equation for the reaction stating the physical state of the reactant & the products. [5 marks] [CBSE 2019]
       Sol:
       1.
       (i) Take 2g white lead nitrate powder in a boiling test tube.
       (ii) Heat the boiling test tube over the flame of a burner using the tong.
       (iii) Observe what happened when you are heating lead nitrate in a boiling test tube.
       2.