Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate

Question

(i) Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate. Give an activity to illustrate how these two are inter convertible.

(ii) Write chemical names and formulae of plaster of paris and gypsum.

Answer 1

(i) Hydrated copper sulphate – CuSO4.5H2O
Anhydrous copper sulphate – CuSO4
Solutions
Activity :
(a) Heat a few crystals of copper sulphate in a dry boiling tube.
(b) Add 2 – 3 drops of water on the sample of copper sulphate obtained after heating. Water is removed and salt turns white. If crystals are moisten again with water, blue colour reappears. Water of crystallisation is fixed number of water molecules present in one formula unit of a salt. Five water molecules are present in one formula unit of copper sulphate.
(ii) Calcium sulphate hemihydrate — CaSO4.H2O (Plaster of paris)
Calcium sulphate dihydrate — CaSO4.2H2O (Gypsum)
OR
(i) Chemical name — Sodium carbonate decahydrate
Formula — Na2CO3.10H2O
(ii) NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
2NaHCO3 → Na2CO3 + CO2↑ + H2O
Na2CO3 + 10H2O → Na2CO3.10H2O
(iii) It is a basic salt because when dissolved in water, it gives a strong base NaOH. It is used as a cleaning agent, in paper and glass industry.