CBSE Class 10 Science 2019 · Paper 31/5/1 · Question 16(b)

(a) Compounds that have the same molecular formula but different structural formulae (different arrangements of atoms) are called isomers. (b) The two compounds are propanal, an aldehyde, ${\text{CH}}_3-{\text{CH}}_2-\text{CHO}$, and propanone (acetone), a ketone, ${\text{CH}}_3-\text{CO}-{\text{CH}}_3$. In propanal the C=O group is on the end carbon, which also carries a hydrogen atom; in propanone it is on the middle carbon. Their full structural formulae are drawn in the solution. (c)(i) Ethanol is heated at $443$ K with excess concentrated sulphuric acid, which removes water: ${\text{CH}}_3{\text{CH}}_2\text{OH}\stackrel{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$. (ii) Propanol is heated with alkaline potassium permanganate (or acidified potassium dichromate), which oxidises it: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3{\text{CH}}_2\text{COOH}$.