Question

Which one of these salts will form an acidic solution upon dissolving in water?

:

A)

KOH

B)

NH4Br

C)

NaCN

D)

LiBr

Answer 1

A) KOH + H₂O basic solution of KOH

KOH is a strong base all by itself. It is not a salt. It yields a basic solution.

B) NH₄Br + H₂O ​  NH₄OH + HBr (Hydrobromic acid)

NH₄Br when dissolved in water, produces a cation, NH₄⁺ (weak acid) - Acidic and an anion, Br- (HBr conjugate acid) - Neutral . Hence the resulting salt is Acidic. since NH₄⁺ is stronger, the solution is acidic.

C) NaCN + H₂O ​ NaOH+ HCN (hydrocyanic acid)

NaCN is a salt of a weak acid (HCN) and a strong base (NaOH) and the resulting solution is basic.

LiBr + H₂O ​  LiOH + HBr (Hydrobromic acid)

LiBr is made from a strong acid (HBr) and a strong base (LiOH). A salt formed from a strong acid and strong base is pretty much neutral because the stronger the acid/base, the weaker the conjugate acid/base. Hence the salt is not acidic.