Answer the questions.[Che-5M]

Question 15 Marks

Common salt is a very important raw material as many compounds of industrial use can be prepared from it. Explain, giving chemical equations, the method of preparation of washing soda from sodium chloride. List four industrial/domestic uses of washing soda.

Answer

The method of preparation of washing soda from sodium chloride are as follows
- Concentrated solution of sodium chloride reacts with ammonia and carbon dioxide to obtain sodium hydrogen carbonate and ammonium chloride.
$\mathrm{NaCl}+\mathrm{NH}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{NaHCO}_{3}+\mathrm{NH}_{4} \mathrm{Cl}$
- When sodium hydrogen carbonate is heated strongly, sodium carbonate is obtained.
$ 2 \mathrm{NaHCO}_{3} \xrightarrow{\text { Heat }} \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} $
- Sodium carbonate is dissolved in water to obtain washing soda.
$\mathrm{Na}_{2} \mathrm{CO}_{3}+10 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}$
Uses:
- In glass, soap and paper industries.
- Manufacture of borax.
- As cleaning agent for domestic purposes.
- For removing permanent hardness of water.

View full question & answer→

Question 25 Marks

Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds?

Answer

The water of crystallization is the fixed number of water molecules present in one formula unit of a salt.
For example
$\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}$ (Copper sulfate Penta hydrate) Blue vitriol.
$\mathrm{FeSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ (Ferrous sulfate heptahydrate) Green vitriol.
- By heating these salts they lose their water molecules and hence result in a change in state and color taking place.
- Blue vitriol is blue as it contains 5 molecules of water of crystallization.
- When it is heated, it loses water of crystallisation and becomes anhydrous copper sulfate ( $\mathrm{CuSO}_{4}$ ) which is grey-white.
- On heating green vitriol, anhydrous ferrous sulfate $\left(\mathrm{FeSO}_{4}\right)$ is formed, which is white.
- Anhydrous ferrous sulfate ( $\mathrm{FeSO}_{4}$ ) on further heating, decomposes into ferric oxide ( $\mathrm{Fe}_{2} \mathrm{O}_{3}$ ), Sulfur dioxide ( $\mathrm{SO}_{2}$ ), and sulfur trioxide ( $\mathrm{SO}_{3}$ ) gas is released.

View full question & answer→

Science Answer the questions.[Che-5M]

Test yourself on this topic