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ICSE Class 10 Chemistry Question 19 of 28

Acids, Bases and Salts — Question 4

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Question

Question 4

How would you prepare :

(a) copper sulphate crystals from a mixture of charcoal and black copper oxide.

(b) zinc sulphate crystals from zinc dust (powdered zinc and zinc oxide),

(c) sodium hydrogen carbonate crystals.

(d) calcium sulphate from calcium carbonate.

Answer

(a) Copper sulphate crystals from a mixture of charcoal and black copper oxide

Method of preparation: Neutralization of insoluble base

Reaction:
CuO + H2SO4 ⟶ CuSO4 + H2O
CuSO4 + 5H2O ⟶ CuSO4.5H2O (blue vitriol)

Procedure:

  1. Take dilute sulphuric acid in a beaker and heat it on wire gauze.
  2. Add black cupric oxide in small quantities at a time, with stirring till no more of it dissolves and the excess compound settles to the bottom.
  3. Filter it hot and collect the filtrate in a china dish. Evaporate the filtrate by heating to the point of crystallization and then allow it to cool and
  4. Collect the bright blue crystals of copper (II) sulphate pentahydrate CuSO4.5H2O (blue vitriol) and dry the crystals.

(b) Zinc sulphate crystals from Zinc dust

Method of preparation: Displacement — By the action of dilute acid (dil. H2SO4) on an active metal (Zinc, Iron).

Reaction:
Zn(s) + H2SO4(aq) ⟶ ZnSO4 + H2↑
ZnSO4 + 7H2O ⟶ ZnSO4.7H2O (white vitriol)

Procedure:

  1. Take dilute sulphuric acid in a beaker and heat it on a wire gauze. Add some granulated zinc pieces with constant stirring.
  2. Effervescence take place because of the liberation of hydrogen gas.
    Add zinc till the Zinc settles at the base of the beaker.
    When effervescence stops, it indicates that all the acid has been used up.
  3. The excess of zinc is filtered off.
  4. Collect the solution in a china dish and evaporate the solution to get crystals. Filter, wash them with water and dry them between the folds of a filter paper. The white, needle-shaped crystals are of hydrated Zinc sulphate.

(c) Sodium hydrogen carbonate crystals:

Method of preparation: By passing carbon dioxide gas into a cold solution of sodium carbonate.

Reaction:
Na2CO3 + CO2 + H2O ⟶ 2NaHCO3

Procedure:

  1. Dissolve 5 grams of anhydrous sodium carbonate in about 25 cm3 of distilled water in a flask.
  2. Cool the solution by keeping the flask in a freezing mixture.
  3. Pass carbon dioxide gas in the solution.
  4. Crystals of sodium bicarbonate will precipitate out after some time.
  5. Filter the crystals and dry it in the folds of filter paper.

(d) calcium sulphate from calcium carbonate.

Method of preparation: By Double Decomposition (precipitation)

Reaction:
CaCO3 + 2HNO3 ⟶ Ca(NO3)2 + H2O + CO2↑
Ca(NO3)2 + Na2SO4 ⟶ CaSO4↓ + 2NaNO3

Procedure:

  1. First insoluble Calcium Carbonate [CaCO3] is converted to soluble Calcium Nitrate [Ca(NO3)2] with the help of dilute nitric acid.
  2. The resulting solution is then treated with Sodium Sulphate [Na2SO4] and a precipitate of Calcium Sulphate is obtained.