Question

$C{H}_{3}CHO$ and $C_6{H}_{5}C{H}_{2}CHO$ can be distinguished chemically by :

• A. Iodoform test
• B. Tollen's reagent test
• C. Fehling solution test
• D. Benedict test

Answer 1

Answer: (A)

$C{H}_{3}CHO$ and $C_6{H}_{5}C{H}_{2}CHO$ are aliphatic aldehydes and hence react with Tollen's reagent, Febling- solution and Benedict solution. These reagents cannot be used to distinguish them $C{H}_{3}CHO$ reacts with $NaOH$ and $I_2$ to form yellow crystalline iodoform while $C_6{H}_{5}C{H}_{2}CHO$ does not react with it.
$\mathrm{CH}{}_3\mathrm{CHO}+3\mathrm{I}{}_2+4\mathrm{NaOH}\to \underset{\mathrm{Yellow}\mathrm{crystalline}\mathrm{ppt}}{\mathrm{CHI}{}_3}+3\mathrm{Nal}+3\mathrm{H}{}_2\mathrm{O}$
$C_6{H}_{5}C{H}_{2}CHO+3I_2+4NaOH\to No$reaction
$\therefore$ Iodoform test can be used to distinguish between $C{H}_{3}CHO$ and $C_6{H}_{5}C{H}_{2}CHO$