Question

Identify the cations for the following case:

$\mathrm{NaOH}$ the solution, when added to the solution (A), gives a reddish brown precipitate

Answer 1

• Reaction as per the question is given below:

$\underset{\mathrm{Ferric}\mathrm{chloride}}{{\mathrm{FeCl}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{3\mathrm{NaOH}\left(\mathrm{s}\right)}\to \underset{\mathrm{Ferric}\mathrm{hydroxide}}{\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{chloride}}{3\mathrm{NaCl}\left(\mathrm{s}\right)}$

• Ferric chloride $\left({\mathrm{FeCl}}_3\right)$ reacts with Sodium hydroxide $\left(\mathrm{NaOH}\right)$ undergoes a double decomposition reaction to gives an insoluble compound in the form of a reddish brown precipitate of Ferric hydroxide $\left(\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\right)$and another soluble compound Sodium chloride$\left(\mathrm{NaCl}\right)$ as products.
• The reaction in which radicals are exchanged in their solution state is known as the double decomposition (double displacement) reaction.
• Thus, the solution (A) which is added is Sodium hydroxide.