CBSE Class 10 Science 2020 · Paper 31/1/1 · Question 17

(i) 5 g of potassium permanganate (${\text{KMnO}}_4$) is dissolved in water and the volume is made up to 100 mL, that is, 5 g of ${\text{KMnO}}_4$ in about 100 mL of water. (ii) Alkaline potassium permanganate acts as an oxidising agent: it supplies oxygen that oxidises ethanol to ethanoic acid, and its purple colour disappears as it is used up. When it is added in excess, the purple colour persists, because no ethanol is left to be oxidised. (iii) ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ (ethanol to ethanoic acid).