(a) Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate. Giving an activity illustrate how these are interconvertible.
(b) Write chemical names and formula of plaster of Paris and gypsum.
(a) CuSO4.5H2O is hydrated copper sulphate. CuSO4 is anhydrous copper sulphate.
Aim: To show crystalline salts contain water of crystallization.
Material Required: CuSO4.5H2O (Blue vitriol), boiling tube, burner, cork, delivery tube, test tube, clamp stand.
Procedure:
1. Take 2g of CuSO4.5H2O in a boiling tube fitted in a clamp stand.
2. Observe its colour. Fit it with cork and delivery tube bent at two right angles which dips into a test tube.
3. Heat crystals in boiling tube.
4. Observe vapours being condensed in test tube.
5. Cool the crystals and add few drops of water into it.
Observation: Water vapours get condensed in a test tube and colour of blue crystals changes into white. On adding water to anhydrous copper sulphate it changes into blue again.
Chemical Reaction :
CuSO4.5H2O + heat →CuSO4 + 5H2O
Conclusion : Crystalline substances have water of crystallization which are lost on heating. When we add water in CuSO4 till a saturated solution is formed. On cooling, it gets converted into CuSO4.5H2O crystals and it shows that both are inter convertible.
(b) CaSO4.1/2H2O Calcium sulphate hemihydrate
CaSO4.2H2O Calcium sulphate dihydrate