Question

What happens when $NaB{H_4}$ is dissolved in water?
A. It decomposes with the evaluation of ${H_2}$ .
B. $N{a^ + }$ and $B{H_4}^ -$ are formed, which are stable.
C. $B{H_4}^ -$ ions formed initially, decompose to produce $O{H^ - }$ ions, which prevent further decomposition.
D. $NaH$ and ${B_2}{H_6}$ are produced.

Answer 1

Sodium borohydride is crystalline powder with the color appearance of white to grayish. It is a very strong reducing agent with the molecular formula $NaB{H_4}$ . When it is dissolved in water some ions are formed initially and hydrogen gas as a by-product, sodium hydroxide ions prevent further decomposition.

Complete answer:
The major application of sodium borohydride is the production of sodium dithionite from sulphur dioxide and Sodium dithionite is used as a bleaching agent for wood pulp and in the dyeing industry.
As sodium hydride is soluble in water but when it is dissolved in water, it reacts with water and as a by-product hydrogen gas is formed which is extremely flammable. Also when it is dissolved in water, sodium borohydride decomposes to form sodium hydroxide ions and hydrogen gas. The formation of sodium hydroxide ions prevents the further decomposition of the salt.

So, Option C is correct.
Note:
Sodium borohydride is a strong reducing agent and hence reduces many organic compounds mostly carbonyls depending on the conditions at which reaction takes place. Generally it is used in the conversion of ketones and aldehydes to alcohols. It mainly reduces acyl chlorides, anhydrides, thioesters, and imines at room temperature or below to the room temperature. $NaB{H_4}$ reacts with water and also with alcohols and evolves hydrogen gas and borates, the reaction being especially fast at low $pH$ .
Sodium borohydride also reduces aldehydes and ketones to give the related alcohols. This application is used in the production of various antibiotics. Various steroids and vitamin A are prepared using sodium borohydride in at least one step. Sodium borohydride is also used to reduce foxing in old books and documents.