Question

${Fe\left(OH\right)}_3$ can be separated from ${Al\left(OH\right)}_3$ by the addition of:

• A. $NaCl$ solution
• B. dil.$HCl$ solution
• C. $NaOH$ solution
• D. ${NH}_{4}Cl$ and ${NH}_{4}OH$

Answer 1

The correct option is C $NaOH$ solution

${Fe}^{3+}$ and ${Al}^{3+}$ both beongs to group IIIrd of inorganic analysis and both are precipitated as their hydroxides on adding group reagent, ie, ${NH}_{4}OH$ in presence of ${NH}_{4}Cl$.
${Fe}^{3+}+3{OH}^{-}⟶{Fe\left(OH\right)}_3$
${Al}^{3+}3{OH}^{-}⟶{Al\left(OH\right)}_3$
but only ppt of ${Al\left(OH\right)}_3$ is soluble in $NaOH$ solution.