Question

Which solution gives a white precipitate with excess ammonium hydroxide solution.

• A. Zinc Chloride
• B. Ferrous chloride
• C. Ferric chloride
• D. Copper chloride

Answer 1

The correct option is A

Zinc Chloride

Explanation for the correct answer:-

Option (A) Zinc Chloride

• When Zinc chloride reacts with Ammonium hydroxide, it forms a white gelatinous ppt of Zinc hydroxide along with Ammonium chloride
• Upon further addition of Ammonium hydroxide dissolves this ppt.
• The complete reaction is:

$$\begin{gathered} \underset{\mathrm{Zinc}\mathrm{chloride}}{{\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonum}\mathrm{hydroxide}}{2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Zinc}\mathrm{hydroxide}}{\mathrm{Zn}(\mathrm{OH}{)}_2\downarrow (\mathrm{s}\left)\right(\mathrm{white})}+\underset{\mathrm{Ammonium}\mathrm{chloride}}{2{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)} \\ \underset{\mathrm{Zinc}\mathrm{hydroxide}}{\mathrm{Zn}(\mathrm{OH}{)}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{chloride}}{2{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonum}\mathrm{hydroxide}}{2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{excess}\right)\left(\mathrm{aq}\right)}\to \underset{\mathrm{tetraamminezinc}\left(\mathrm{II}\right)\mathrm{chloride}}{{\left[\mathrm{Zn}{\left({\mathrm{NH}}_3\right)}_4\right]}_2{\mathrm{Cl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)} \end{gathered}$$

• Hence it is the correct option.

Explanation for the incorrect answer:-

Option (A) Ferrous chloride

• When Ferrous chloride reacts with Ammonium hydroxide to form Ammonium chloride and a green ppt of Ferrous hydroxide.
• The complete reaction is:

$\underset{\mathrm{Ferrous}\mathrm{chloride}}{{\mathrm{FeCl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{hydroxide}}{2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)}⟶\underset{\mathrm{Ammonium}\mathrm{chloride}}{2{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Ferrous}\mathrm{hydroxide}}{\mathrm{Fe}(\mathrm{OH}{)}_2\left(\mathrm{s}\right)(\downarrow )\left(\mathrm{green}\right)}$

• Hence it is the incorrect option.

Option (A) Ferric chloride

• When Ferric chloride reacts with Ammonium hydroxide to form Ammonium chloride and a reddish-brown ppt of Ferric hydroxide.
• The complete reaction is:

$\underset{\mathrm{Ferric}\mathrm{chloride}}{{\mathrm{FeCl}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Ammonium}\mathrm{hydroxide}}{3{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)}⟶\underset{\mathrm{Ammonium}\mathrm{chloride}}{3{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Ferric}\mathrm{hydroxide}}{\mathrm{Fe}(\mathrm{OH}{)}_3\left(\mathrm{s}\right)(\downarrow )(\mathrm{reddish}-\mathrm{brown})}$

• Hence it is the incorrect option.

Option (A) Copper chloride

• When Copper chloride reacts with Ammonium hydroxide to form Ammonium chloride and a pale blue ppt of Copper hydroxide.
• This Copper hydroxide dissolves in excess Ammonium hydroxide and forms a deep blue colouration of Tetrammine copper(II) chloride.
• The complete reaction is:

$$\begin{gathered} \underset{\mathrm{Cooper}\mathrm{chloride}}{{\mathrm{CuCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Ammonium}\mathrm{hydroxide}}{2{\mathrm{NH}}_4\mathrm{OH}\left(\mathrm{aq}\right)}⟶\underset{\mathrm{Ammonium}\mathrm{chloride}}{2{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Copper}\mathrm{hydroxide}}{\mathrm{Cu}(\mathrm{OH}{)}_2\left(\mathrm{s}\right)(\downarrow )(\mathrm{pale}\mathrm{blue})} \\ \underset{\mathrm{Copper}\mathrm{hydroxide}}{\mathrm{Cu}\left(\mathrm{OH}{)}_2\right(\mathrm{s})}+\underset{\mathrm{Ammonium}\mathrm{chloride}}{4{\mathrm{NH}}_4\mathrm{Cl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Tetrammine}\mathrm{copper}\left(\mathrm{II}\right)\mathrm{chloride}}{\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]·2\mathrm{Cl}\left(\mathrm{aq}\right)(\mathrm{Deep}\mathrm{blue})}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Hydrochloric}}{2\mathrm{HCl}\left(\mathrm{aq}\right)} \end{gathered}$$

• Hence it is the incorrect option.