Question

Consider the reaction: $BCl_{3}+6NH_{3} \longrightarrow B(NH_{2})_{3}+3NH_{4}Cl$, what do you infer about acidic/basic character of $BCl_{3}$?

Answer 1

$BCl_3 +6NH_3\rightarrow B(NH_2)_3+ 3(NH_4^+ +Cl^-)$

Boron Trichloride- when added to weak base ammonia that is $NH_3$ gives 3 ammonium cations and 3 chlorine anions.

The ammonium ion formed is acidic in nature.

So, we know that on dissolving boron trichloride in ammonia we shall get a solution with (an ammonium ion) $NH^{4+}$ that makes the solution acidic. So even if the solution has a base involved the reaction shall make the solution acidic.

Answer 2

Answer:

A molecule is said to be a lewis acid if it can accept a lone pair.

When the halide is more electronegative the interelectronic repulsion increases making the molecule difficult to accept a lone pair.

Size of halide also behaves in the same way. Also the degree of hydrolysis increases from fluorine to iodine,so the lewis acidic character increases in the same order.

So,the order of lewis acidity is BBr

3

>BCl

3

>BF

3

.

Hence, the correct option is B.