Question

Tollen's reagent gives .................. with acetaldehyde

• A. brown fumes
• B. pink solution
• C. silver mirror
• D. none of these

Answer 1

Answer: (C)

silver mirror

Tollen's reagent gives silver mirror with acetaldehyde. Tollens' reagent contains the diamminesilver(I) ion, $\left[Ag\right(N{H}_3{)}_2{]}^{+}$. This is made from silver(I) nitrate solution. Aldehydes reduce the diamminesilver(I) ion to metallic silver. Because the solution is alkaline, the aldehyde itself is oxidised to a salt of the corresponding carboxylic acid. The colourless solution produces a grey precipitate of silver, or a silver mirror on the test tube.

$2\left[Ag\right(N{H}_3{)}_2{]}^{+}+RCHO+3O{H}^{-}\to 2Ag+RCO{O}^{-}+4N{H}_3+2H_{2}O$