Class 10 Acids, Bases and Salts Previous Years Questions : Solutions

Acids, Bases and Salts Previous Years Questions : Solutions

1. If 10 ml of H₂SO₄ is mixed with 10 ml of Mg(OH)₂ of the same concentration, the resultant solution will give the following colour with universal indicator: [1 Mark] [CBSE 2020]
   1. Red
   2. Yellow
   3. Green
   4. Blue
      Sol:
      The Correct option is (c) Green
2. 2 mL of sodium hydroxide is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed, a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with dilute solution of a strong acid. [3 Marks] [CBSE 2018]
   Sol:
   When Zinc (Zn) is added to solution of sodium Hydroxide (NaOH) :
   2NaOH + Zn → Na₂ZnO₂ + H₂
   Here, The product form is Sodium Zincate (Na₂ZnO₂) and Evolution of Hydrogen (H₂)
   Hydrogen Gas test : When a burning candle is held near the evolved it continues burning with pop sound indicating Evolution of Hydrogen gas.
   Zinc reacts with a strong acid forms:
   Zn + H₂SO₄ → ZnSO₄ + H₂ ↑
3. The pH of salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses. [3 Marks] [CBSE 2018]
   Sol:
   Salt is Baking Soda, NaHCO₃ ( Sodium Bicarbonate or, Sodium Hydrogen Carbonate)
   The reaction involved in the formation of NaHCO₃ :
   NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
   Uses of Baking soda (NaHCO₃) :
   (i) It is used as an antacid.
   (ii) It is used in soda-acid fire extinguishers.
4. State the effect of concentration of H⁺ (aq) ions on the nature of the solution. Do basic solutions also have H⁺ (aq) ions ? If yes, then why are these basic? [3 Marks] [CBSE 2019]
   Sol:
   The concentration of H⁺ in a solution determines the nature of the soluton is acidic. If the concentration of H⁺ ions will increases then the solution will be more acidic and if the concentration of OH^– ions will increases then the solution will be basic.
   yes, basic solutions also have H⁺ ions But they act as basic because the concentration of OH^– ions is much more than H⁺ ions in a solution.
5. Write the chemical formula of washing soda. How can it be obtained from baking soda ? List two industries in which washing soda is used for other purposes than washing clothes. [3 Marks] [CBSE 2019]
   Sol:
   The chemical formula of Washing soda is (Na₂CO₃.10H₂O) Hydrated Sodium bicarbonate.
   2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
   Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O
   Uses :
   (i) It is used in glass, soap and paper industries.
   (ii) It is used as a cleansing agent in industries.
6. A chemical compound ‘X’ is used in the soap and glass industry. It is prepared from brine.
   1. Write the chemical name, common name and chemical formula of ‘X’.
   2. Write the equation involved in its preparation.
   3. What happens when it is treated with water containing Ca or Mg salts? [3 Marks] [CBSE 2020]
      Sol:
      (1) The chemical name of X is Hydrated Sodium carbonate.
      The common name is washing soda.
      The chemical formula is Na₂CO₃.10H₂O
      (2) The equation involved in its formation :
      NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
      2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
      Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O
      (3) Washing soda helps in removing of permanent hardness of water. It forms insoluble Ca or Mg salts in the form of scum when it is treated with water containing Ca or Mg salts.