Question

Identify the reagent that separates fe3+ from zn2+. explain the chemistry of the separation

Answer 1

The reagent that can separate Fe³⁺ from Zn²⁺ is NaOH.

Explanation :

NaOH precipitates Fe³⁺ and Zn²⁺ ions in the form of their insoluble hydroxides.

The net ionic equations for these reactions are given below.

$Fe^{3+} (aq)+ 3OH^{-}(aq)\rightarrow Fe(OH)_{3}(s)$

$Zn^{2+} (aq)+ 2OH^{-}(aq)\rightarrow Zn(OH)_{2}(s)$

But when excess of NaOH is added, Zinc hydroxide forms a soluble complex ion known as "zincate" ion and gets dissolved in the solution . The reaction is given below.

$Zn^{2+} (aq)+ 4OH^{-}(aq)\rightarrow [Zn(OH)_{4}]^{2-}(aq)$

Therefore in order to separate a mixture of Fe³⁺ and Zn²⁺, we have to add excess of NaOH and boil the mixture in water bath to ensure that the reaction goes to completion.

During this process, Fe³⁺ gets precipitated as Fe(OH)₃ whereas Zn²⁺ forms a soluble complex ion [Zn(OH)₄]²⁻ which remains in the solution.

When we filter the mixture, Fe³⁺ gets filtered off as a precipitate whereas Zn²⁺ remains in the solution. In this manner , the given ions can be separated.