Question

The molecule which is not hydrolyzed by water at $25$ degree celsius is__?

• A. ${\mathrm{AlCl}}_3$
• B. ${\mathrm{SiCl}}_4$
• C. ${\mathrm{BF}}_3$
• D. ${\mathrm{SF}}_6$

Answer 1

The correct option is D

${\mathrm{SF}}_6$

Explanation for correct option

(D)${\mathrm{SF}}_6$

Hydrolysis

• Decomposition of a chemical compound on reacting with water is called as hydrolysis.
• The reaction involves splitting of a bond and the addition of the hydrogen cation and the hydroxide anion of water.

Sulfur hexafluoride

• Sulfur hexafluoride (${\mathrm{SF}}_6$) is an inert gas. Due to the presence of sterically protected sulfur atom by six fluorine atoms which does not permit the reactions with water.

Explanation for incorrect options

• Aluminum chloride$\left({\mathrm{AlCl}}_3\right)$reacts with water to from aluminum hydroxide $\left(\mathrm{Al}{\left(\mathrm{OH}\right)}_3\right)$and Hydrogen chloride $\left(\mathrm{HCl}\right)$ gas. ${\mathrm{AlCl}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\to \mathrm{Al}{\left(\mathrm{OH}\right)}_3\left(\mathrm{aq}\right)+3\mathrm{HCl}\left(\mathrm{l}\right)$
• Silicon tetrachloride (${\mathrm{SiCl}}_4$) gets hydrolyzed to form Silicic acid $\left(\mathrm{Si}{\left(\mathrm{OH}\right)}_4\right)$ and fumes of Hydrogen chloride$\left(\mathrm{HCl}\right)$. ${\mathrm{SiCl}}_4\left(\mathrm{l}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Si}{\left(\mathrm{OH}\right)}_4\left(\mathrm{aq}\right)+4\mathrm{HCl}\left(\mathrm{aq}\right)$
• Boron trifluoride reacts with water to form boric acid $\left({\mathrm{H}}_3{\mathrm{BO}}_3\right)$ and fluoroboric acid $\left({\mathrm{HBF}}_4\right)$.
• $4{\mathrm{BF}}_3\left(\mathrm{g}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_3{\mathrm{BO}}_3\left(\mathrm{s}\right)+3{\mathrm{HBF}}_4\left(\mathrm{l}\right)$
• Hence, options (A), (B), and (C) are incorrect.

Hence, option (D) is correct. The molecule which is not hydrolyzed by water at $25$ degree celsius is ${\mathrm{SF}}_6$.