Question

Give a chemical test to distinguish between the following pairs of compounds.

Iron II chloride and Iron III chloride solution

Answer 1

Part1:- Test for Iron II chloride and Iron III chloride solution

1. A dirty green precipitate of iron (II) hydroxide is generated when $\mathrm{NaOH}$ solution is added.
2. When Sodium Hydroxide is added to an iron chloride solution, a dirty green precipitate appears, and that dirty green precipitate is due to the formation of Ferrous Hydroxide $\left[\mathrm{Fe}{\left(\mathrm{OH}\right)}_2\right]$ and$\mathrm{NaCl}$, is obtained. When${\mathrm{FeCl}}_3$, which is Iron III chloride, reacts with $\mathrm{NaOH}$ solution a reddish-brown precipitate of Ferric hydroxide$\left[\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\right]$ and$\mathrm{NaCl}$, is obtained.
3. So, if there are dirty green precipitates, it indicates the presence of Iron (II) chloride, and if there is a reddish-brown precipitate, it indicates the presence of Ferric chloride, which is Iron III chloride solution.

Part 2: Reactions involved

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

$$\begin{gathered} {\mathrm{FeCl}}_3\left(\mathrm{aq}\right)+3\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_3\left(\mathrm{s}\right)+3\mathrm{NaCl}\left(\mathrm{aq}\right) \\ (\mathrm{Iron}(\mathrm{III})(\mathrm{Sodium}\left(\mathrm{Iron}\right(\mathrm{III})(\mathrm{Sodium} \\ \mathrm{chloride})\mathrm{hydroxide})\mathrm{hydroxide})\mathrm{chloride}) \end{gathered}$$

Final Answer:-

When $\mathrm{NaOH}$ solution is added to the aforementioned solutions, Iron (II) chloride produces dirty green ppt. whereas Iron (III) chloride produces reddish-brown ppt.