Question

Write the molecular formula of a salt that, when dissolved in water, produces the solution with an basic Ph?

Answer 1

1) Any species which dissociates in water to give Hydroxyl (OH-) ion and counter cation produce a basic solution.

The general formual for such a salt is Mx(OH)y.Which dissociates as,

Mx(OH)y ----------> xM⁺ + yOH^- .

e.g. NaOH, KOH, Ba(OH)2 etc.

2) The salt of weak acid and strong base also on dissolution in water produces solution with basic of alkaline pH (pH>7)

Dissolution of salt in water is termed as hydrolysis of salt.

Hydrolysis of salt of weak acid and strong base is represented as,

BA + H2O <------------> BOH + HA

Salt Base (strong) Acid (weak)

BOH being strong base ionizes in water completely as, BOH -------> B⁺ + OH^- .

and HA being weak acid ionizes only slightly in water as, AH <----------> A^- + H⁺ .

Hence there is far greater concentration of OH- ions than H+ ions which produces basicity in the solution formed.

e.g. Sodium acetate (CH3COO^-Na⁺) salt. It is a salt of weak organic acid (CH3COOH acetic acid) and strong base (NaOH). I.e. a salt of weak acid and strong base. Hence aqueous solution of sodium acetate will form solution with basic pH (pH>7).