- Acidic salts
- Basic salts
- Neutral salts
Let us discuss hydrolysis of salts of the following types:
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Salts of strong acid and strong base: Salts formed by the neutralization of strong acid and strong base are neutral in nature as the bonds in the salt solution will not break apart. They generally get hydrated but do not hydrolyse. Therefore, such salts are generally known as neutral salts.
For example: \(NaCl\)
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Salts of weak acid and strong base: Salts formed by the neutralization of weak acid and strong base are basic in nature. For example: \(CH_3COONa\)
\(CH_3COONa~ (aq)~ →~CH_3COO^-~ (aq)~+~ Na^+~ (aq)\)
Acetate ion formed undergoes hydrolysis to form acetic acid and OH– ions.\( CH_3COO^-(aq)~ +~ H_2O~⇋ ~CH_3COOH (aq)~ +~ OH^- (aq) \)As we know acetic acid is a weak acid, it remains unionized in the solution. This results in an increase in concentration of OH– ions which makes the solution alkaline.pH of the solution is greater than7.
Salts of strong acid and weak base: Salts formed by the neutralization of strong acid and weak base are acidic in nature. For example: \( NH_4Cl\)
\( NH_4Cl (aq) ~→ ~Cl^-(aq)~ +~ NH_4^+ (aq)\)
\( NH_4^+ (aq) ~+~ H_2O~ ⇋~ NH_4OH (aq)~ +~ H^+ (aq)\)
\(CH_3COO^- ~+ ~NH_4^+~ +~ H_2O ~⇋~ CH_3COOH ~+~ NH_4OH\)
Degree of hydrolysis in such cases is independent of the concentration of solution and pH of such solutions is given by:
pH= 7 + \( \frac 12 \) (pKa – pKb)
Hence, we can say that the pH of a solution can be less than 7 or greater than 7 depending on the values of pKa and pKb.
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