CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 5

The purple colour of the alkaline potassium permanganate disappears as each drop is added, because it is used up in oxidising the propanol; once all the propanol has been oxidised, the purple colour of further drops persists. Alkaline ${\text{KMnO}}_4$ acts as an oxidising agent, and propyl alcohol (propanol) is oxidised to propanoic acid: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3{\text{CH}}_2\text{COOH}$ or ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}+2[\text{O}]\to {\text{CH}}_3{\text{CH}}_2\text{COOH}+{\text{H}}_2\text{O}$.