Question

What colour precipitates are formed when aqueous ammonia reacts with:

Ferrous sulphate
State the solubility of each precipitate in excess of ammonium hydroxide.

Answer 1

Reaction with iron(II) sulphate (Ferrous sulphate) ($\left({\mathrm{FeSO}}_4\right)$:

• Ammonium hydroxide reacts with iron(II) sulphate solution to form a dirty green colored precipitate of $\mathrm{Fe}(\mathrm{OH}{)}_2$, which is insoluble in excess of ammonium hydroxide.
• One mole of Ferrous sulphate reacts with two moles of Ammonium hydroxide to form one mole of $\mathrm{Fe}(\mathrm{OH}{)}_2$ and one mole of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$.
• ${\mathrm{FeSO}}_4\left(\mathrm{aq}\right)+2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)⟶\mathrm{Fe}(\mathrm{OH}{)}_2\left(\mathrm{s}\right)\downarrow +{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4(\mathrm{aq})$

Therefore, dirty green colored precipitate is formed when aqueous ammonia reacts with ferrous sulphate which is insoluble in excess of ammonium hydroxide.