Question

Most chloride compounds are water soluble.
Which of the following chloride compounds is NOT soluble in water?

• A. $Fe{Cl}_3$
• B. $NaCl$
• C. $Ca{Cl}_2$
• D. $Pb{Cl}_2$
• E. $Al{Cl}_3$

Answer 1

Answer: (A)

$Fe{Cl}_3$

FeCl${}_3$ is a salt of weak base and strong acid. So, the rate of dissociation of Cl${}^{-}$ ions is very high that=n Fe${}^{3+}$ ions in water. So, in water, we have more undissociated Fe (OH)${}_3$ and more dissociated Cl${}^{-}$ ions and H${}^{+}$ ion. So, the following equilibrium is achieved:

$F{e}^{3+}$ (aq) + $H_{2}O$ $\rightleftharpoons$ $Fe\left(O{H}_3\right)$ (aq) + $H^{+}$ (aq)

Now, Fe ${}^{3+}$ ions tends to combine with OH${}^{-}$ in the solution and in accordance with LeChatelier's principle the equilibrium shifts towards $Fe(OH{)}_3$

So, a precipitate of $Fe(OH{)}_3$ is formed. Hence, $FeC{l}_3$ is not soluble in water.

$FeC{l}_3$+ $3H_{2}O$ $\to$ $Fe(OH{)}_3$ +$3HCl$