CBSE Class 10 Science 2020 · Paper 31/3/1 · Question 26

(a) Composition: soaps are sodium or potassium salts of long-chain carboxylic (fatty) acids, whereas detergents are generally ammonium or sulphonate salts that also have a long hydrocarbon chain (sodium salts of long-chain sulphonic acids, or ammonium salts with chloride or bromide ions): their charged end is a sulphonate or ammonium group instead of the carboxylate group of a soap. Cleansing action in hard water: soaps react with the calcium and magnesium ions of hard water and form an insoluble scum, so they do not clean well; detergents do not form any scum and clean well even in hard water. (b) Sodium reacts with ethanol, evolving hydrogen gas and forming sodium ethoxide: $2\text{Na}+2{\text{CH}}_3{\text{CH}}_2\text{OH}⟶2{\text{CH}}_3{\text{CH}}_2{\text{O}}^{-}{\text{Na}}^{+}+{\text{H}}_2$. Ethanol behaves like an acid in this reaction. (c) Cyclohexane, ${\text{C}}_6{\text{H}}_{12}$: six carbon atoms joined by single bonds in a ring, each carbon bonded to two hydrogen atoms (structure drawn in the solution). (d) Ethanal (acetaldehyde), ${\text{CH}}_3\text{CHO}$.