Question

Which one of these salts will form a basic solution upon dissolving in water?

A) KBr

B) KClO3

C) LiCl

D) NaNO3

E) NH4NO3

Please explain how you got the answer for my own reference, I really appreciate it.

Answer 1

Let AB be the salt of an acid AH and the base HOB.

There are 2 possibilities with AH and HOB i.e. AH can be strong/weak acid and HOB can be strong/weak base.

Depending on this we can have 4 possible combinations as,

i)AH –Strong acid, HOB- Strong base (SASB)

ii)AH- Strong acid, HOB- Weak Base (SAWB)

iii)AH-Weak acid , HOB-Strong base (WASB)

iv)AH- Weak acid, HOB- Weak base (WAWB)

And depending on this AB can be a salt of SASB, SAWB, WASB, WAWB.

When salt dissolves in water it get hydrated back to its constituent acid and base (from which it was formed)

AB + H-OH ------------ > AH + HOB.

And these acid and base dissociates in water as per there strength. i.e. strong acid/base dissociates completely and weak dissociates partially.

If on hydrolysis we get weak AH and strong HOB formation then there will be very high concentration of OH^- (hydroxyl ion) and H⁺ proton concentration will be very small. Hence very few OH^- ions will neutralize these H⁺ ions and very large number of OH^- ions will remains in the solution which makes the solution basic.

Hence we can say that a salt of WASB (Weak acid Strong Base) on dissolution in water makes the solution basic.

Simmilarly,

A salt of SASB will make solution neutral as both acid and base are strong hence ionizes completely and equal concentration of H⁺ and OH^- ions. Net solution is neutral.

A salt solution of SAWB will be acidic.

A salt solution of WAWB will acidic if acid formed is comparively more stronger than that of base. And it will be basic if base formed is comparatively stronger than acid.

Let us have solvation reactions of all salts.

A) KBr

KBr + H-OH --------- > KOH + HBr

Both KOH and HBr are strong and hence solution will be neutral.

B) KClO3

KClO3 + H-OH --------- > KOH + HClO3

KOH is strong base and HClO3(chloric acid) is comparatively weak acid and hence solution will be Basic.

C) LiCl

LiCl + H-OH ------- > LiOH + HCl

Both LiOH and HCl are strong hence solution will be neutral.

D) NaNO3

NaNO3 + H-OH ------ > NaOH + HNO3

Both NaOH and HNO3(Nitric acid) are strong hence solution will be neutral.

E) NH4NO3

NH4NO3 + H-OH -------> NH4OH + HNO3

NH4OH is weak base and HNO3 is strong acid hence solution will be acidic.

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