CBSE Class 10 Science 2020 · Paper 31/3/2 · Question 26

(a) (i) Ethanol heated at 443 K with excess concentrated sulphuric acid loses water (dehydration): ${\text{CH}}_3{\text{CH}}_2\text{OH}\underset{443\text{K}}{\overset{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$ (ii) Ethanol heated with alkaline potassium permanganate (or acidified potassium dichromate) is oxidised: ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{alkaline KMnO}}_4+\text{heat}}{\to }{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ (b) Addition reaction: an unsaturated compound adds atoms across its double or triple bond, giving a single product; for example, unsaturated hydrocarbons add hydrogen in the presence of a nickel or palladium catalyst to give saturated hydrocarbons: ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni catalyst}}{\to }{\text{CH}}_3-{\text{CH}}_3$ Substitution reaction: one type of atom or group of atoms in a compound takes the place of another, giving two products; for example, in sunlight chlorine replaces a hydrogen atom of methane: ${\text{CH}}_4+{\text{Cl}}_2\stackrel{\text{sunlight}}{\to }{\text{CH}}_3\text{Cl}+\text{HCl}$ (Any other correct example earns credit.)