The chemical formula of washing soda is ${\mathrm{Na}}_2{\mathrm{CO}}_3. 10{\mathrm{H}}_2\mathrm{O}$.

Answer the following questions:

• What does $10 {\mathrm{H}}_2\mathrm{O}$ signify?
• Does it make ${\mathrm{Na}}_2{\mathrm{CO}}_3$ wet?
• Are the crystals of salts really dry?

Answer the following:

Write the formula of a salt that contains water of crystsllisation.

State one relevant observation for the following reactions:

• Addition of excess ammonium hydroxide into copper sulphate solution.

Answer the following:

A calcium compound having odour of chlorine is used to remove yellowish-white clothes in laundries. Name the compound.

State one relevant reason for the following:

• Hydrated copper sulphate crystals turn white on heating.

State:

The difference between number of molecules in Gypsum and in Plaster of Paris.

Give one phrase for the following statement:

The property by which certain hydrated salts, when left exposed to atmosphere, lose their water of crystallization and crumble into powder.