Question

Which compound will form an acidic solution when dissolved in water?

MgSO4

NH4I

NaI

K2CO3

Answer 1

NH4I forms an acidic solution when dissolved in water.

NH4I is a salt of weak base NH4OH and strong acid HI. Thus the NH4+ ion undergoes hydrloysis in water to give an acidic solution.

NH4+ + I- + H2O -----------> NH4OH + H+ + I-

The salts MgSO4 and NaI are salts of strong bases Mg(OH)2 and NaOH with strong acids H2SO4 and HI respectively. They do not undergo hydrolysis, their solutions are neutral .

K2CO3 is a salt of strong base KOH and weak acid H2CO3, thus undergoes hydrolysis to give basic solution in water.