Question

A salt is added to the neutral ferric chloride solution to give deep red colour which on heating decomposes to a brown-red precipitate. Which of the following will be present in the salt?

• A. Nitrite ion
• B. Carbonate ion
• C. Acetate ion
• D. Sulphate ion

Answer 1

The correct option is C Acetate ion

Acetate gives deep red colour on reaction with neutral ferric chloride solution due to the formation of complex ion which decomposes on heating to give Iron (III) dihydroxyacetate as brown red precipitate.
$6C{H}_{3}CO{O}^{–}+3F{e}^{3+}+2H_{2}O\to \left[F{e}_3\right(OH{)}_2(C{H}_{3}COO{)}_6{]}^{+}+2H^{+}[F{e}_3\left(OH{)}_2\right(C{H}_{3}COO{)}_6{]}^{+}+4H_{2}O\to \underset{\text{Iron(III)dihydroxyacetate}\text{(Brown-red precipitate)}}{3\left[Fe\right(OH{)}_2\left(C{H}_{3}COO\right)]}+3C{H}_{3}COOH+H^{+}$