Question

Which one of the following salts when dissolved in water will hydrolyze?
A. \[NaCl\]
B. \[KCl\]
C. \[N{{H}_{4}}Cl\]
D. \[N{{a}_{2}}S{{O}_{4}}\]

Answer 1

Hint: Water is a neutral substance and very little portion of it is present in the ionised form \[\left( {{H}^{+}}\text{ }and\text{ }O{{H}^{-}} \right)\]. When salt is added, weakly bonded salt is hydrolyzed by water molecules such as the cation of salt attracts anion of water, and anion of salt attracts cation of water. If any salt is formed with a strong chemical bond and that salt will be stable and neutral like water and thus, do not get hydrolyzed in water as water is also a neutral substance. Salt is formed with strong acid and the strong base does not get hydrolyzed as the resultant bond is very strong and neutral.

Complete Step by Step Answer:
Sodium chloride, \[NaCl\] a common salt is formed from the reaction of strong acid \[HCl\] with a strong base \[NaOH\]. As they both are very strong thus, strong acids will easily release \[{{H}^{+}}\]ions and strong base release \[O{{H}^{-}}\]ions, release water and thus, give \[NaCl\]salt. So, as per the hint, strong acid and strong base do not get hydrolyzed in water.

Now potassium chloride is formed such as \[NaCl\]. It is formed when strong acid \[HCl\]reacts with a strong base \[KOH\]. Thus, it will also not get hydrolyzed in water because of the strong bond and it is a neutral \[\left( pH\text{ }=\text{ }7 \right)\]compound like water.

Sodium sulphate, \[N{{a}_{2}}S{{O}_{4}}\] a salt formed by the reaction of strong base \[NaOH\] and strong acid \[{{H}_{2}}S{{O}_{4}}\]. Strong acid release \[{{H}^{+}}\]ions and strong base release \[O{{H}^{-}}\] ions releasing out water in a reaction resulting in the formation of sodium sulphate a neutral substance like water. Due to this, it does not get hydrolyzed by water molecules.

Whereas \[N{{H}_{4}}Cl\] is formed when a weak base \[N{{H}_{3}}\] reacts with strong acid \[HCl\]. Strong acid release \[{{H}^{+}}\]ions in aqueous solution and weak base \[N{{H}_{3}}\]in water accept \[{{H}^{+}}\]ion to form hydroxide and thus do not release \[O{{H}^{-}}\] ion in water . Thus, ammonia and hydrochloride do not form strong bonds and the bond will be acidic (pH less than 7).
Thus, the correct option is C.

Note: Acids are those compounds that can easily give \[{{H}^{+}}\] ion in aqueous solution and base release \[O{{H}^{-}}\]ion in aqueous solution. The salt formed with a weak base means the base is not releasing its \[O{{H}^{-}}\] ion easily thus it cannot form a bond easily with strong or weak acid thus, bond will be weak and get hydrolyze easily in water and same case if acid is weak. In short, if the formation of salt involves weak acid or base that salt will get easily hydrolyzed in water otherwise not get hydrolyzed easily.