Q.Describe the important uses of caustic soda.

Sodium hydroxide (caustic soda) is a strong, cheap industrial alkali with wide use across manufacturing industries.

Important uses of caustic soda ($NaOH$):

1. Soap and detergent industry — used to saponify fats and oils in the manufacture of soap.
2. Paper industry — used in pulping wood and processing paper.
3. Textile industry — used for mercerising cotton fabric, improving its strength, lustre, and dye affinity.
4. Metallurgy — used in the Bayer process to purify bauxite ore ($Al_2O_3 \cdot 2H_2O$) during the extraction of aluminium, as it dissolves amphoteric $Al_2O_3$ as sodium aluminate.
5. Rayon (artificial silk) manufacture — used in the viscose process.
6. Petroleum refining — used to remove acidic impurities from petroleum fractions. …

Match each s-block compound to its characteristic property based on its known chemistry.

1. Na2CO3.10H2O (washing soda): On heating (effloresces), it loses its water of crystallisation and converts to anhydrous Na2CO3, known as soda ash → matches (iii) Forms soda ash on heating.
2. NaHCO3 (baking soda): Because it decomposes on heating to release CO2 (which smothers flames), it is used in some fire extinguishers → matches (iv) Used in fire extinguishers.
3. Ca(OH)2 (slaked lime): When chlorine gas is passed over dry slaked lime, it forms calcium oxychloride (bleaching powder) → matches (ii) Preparation of bleaching powder. …