Question

Give one chemical test to distinguish between Iron (II) chloride and iron (III) chloride solution.

Answer 1

• Iron (II) chloride solution reacts with sodium hydroxide solution to form a dirty green precipitate of iron (II) hydroxide, which is insoluble in excess of sodium hydroxide.

$$\begin{gathered} {\mathrm{FeCl}}_2\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right) \\ \mathrm{Iron}\left(\mathrm{II}\right)\mathrm{chloride}\mathrm{Sodium}\mathrm{hydroxide}\mathrm{Iron}\left(\mathrm{II}\right)\mathrm{hydroxide}\mathrm{Sodium}\mathrm{chloride} \end{gathered}$$

• Iron (III) chloride reacts with sodium hydroxide solution to form a reddish brown precipitate of iron (III) hydroxide, which is insoluble in excess of sodium hydroxide.
• $$\begin{gathered} {\mathrm{FeCl}}_3\left(\mathrm{s}\right)+3\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_3\left(\mathrm{aq}\right)+3\mathrm{NaCl}\left(\mathrm{aq}\right) \\ \mathrm{Iron}\left(\mathrm{III}\right)\mathrm{chloride}\mathrm{Sodium}\mathrm{hydroxide}\mathrm{Iron}(\mathrm{III})\mathrm{hydroxide}\mathrm{Sodium}\mathrm{chloride} \end{gathered}$$