Question

Among the following, the number of halide(s) which is/are inert to hydrolysis is ___________: (A) BF$_3$, (B) SiCl$_4$, (C) PCl$_5$, (D) SF$_6$

Hint:

$SF_6$ is so inert that it is used as a gaseous insulator in high-voltage transformers. Its stability is kinetic (steric shielding) rather than purely thermodynamic.

Answer 1

Correct Answer: 1

Step 1: (A) $BF_3$ hydrolyzes partially to give $H_3BO_3$ and $H[BF_4]$.
Step 2: (B) $SiCl_4$ hydrolyzes readily to $Si(OH)_4$.
Step 3: (C) $PCl_5$ hydrolyzes to $POCl_3$ and then $H_3PO_4$.
Step 4: (D) $SF_6$ is inert to hydrolysis. Due to the steric hindrance of 6 Fluorine atoms and the lack of accessible $d$-orbitals (kinetically), water cannot attack the central Sulfur atom.