Question

Which of the following statements is falsc? (1) Hydrolysis of the salt of strong acid and weak base is called cationic hydrolysis (2) Hydrolysis of the salt of weak acid and strong base is known as anionic hydrolysis (3) Aqueous solution of aluminium chloride is acidic due to hydrolysis of \(\mathrm{Al}^{3}\) ion (4) Aqueous solution of sodium carbonate is basic due to hydrolysis of \(\mathrm{Na}\) ion

Short answer

Statement 4 is false because sodium ion does not hydrolyze.

Step-by-step solution

- Analyze Statement 1

Hydrolysis of the salt of a strong acid and a weak base is known as cationic hydrolysis. Since the cation of the weak base hydrolyzes, this statement is correct.

- Analyze Statement 2

Hydrolysis of the salt of a weak acid and a strong base is called anionic hydrolysis. Since the anion of the weak acid hydrolyzes, this statement is correct.

- Analyze Statement 3

Aqueous solution of aluminium chloride is acidic due to hydrolysis of \(\text{Al}^{3+}\) ion. The \(\text{Al}^{3+}\) ion reacts with water to form \(\text{Al(OH)}^{2+}\) and \(\text{H}^{+}\) ions, making the solution acidic. This statement is correct.

- Analyze Statement 4

Aqueous solution of sodium carbonate is basic due to hydrolysis of \(\text{Na}\) ion. This is incorrect because sodium ion (Na\(\text{Na}^{+}\)) from sodium carbonate does not hydrolyze; instead, the carbonate ion (CO_3^{2-}) hydrolyzes to form hydroxide ion (OH^{-}), making the solution basic.

Key concepts

cationic hydrolysis

In cationic hydrolysis, a salt formed from a strong acid and a weak base reacts with water. The cation, which originates from the weak base, hydrolyzes.
For example, consider ammonium chloride (NH4Cl). When it dissolves in water, it forms NH4+ and Cl- ions. The NH4+ ion undergoes cationic hydrolysis by reacting with water to form NH4OH and H+ ions.
This process makes the solution acidic because of the presence of H+ ions.

• The general reaction for cationic hydrolysis can be written as:
  \text{BH\(^{+}\) + H\( _{2} \)O ↔ B + H\(_{3} \)O\(^{+}\)}

anionic hydrolysis

Anionic hydrolysis happens when the salt of a weak acid and a strong base dissolves in water. Here, the anion from the weak acid is the one that hydrolyzes.
For instance, take sodium acetate (CH3COONa). When it dissolves in water, it forms CH3COO- and Na+ ions. The CH3COO- ion undergoes anionic hydrolysis by reacting with water to form CH3COOH and OH- ions.
This process makes the solution basic due to the presence of OH- ions.

• The general reaction for anionic hydrolysis is:
  \text{A- + H\( _{2} \)O ↔ HA + OH\(^{-}\)}

acidic solutions

An acidic solution has an excess of hydrogen ions (H+).
When salts undergo cationic hydrolysis, they often produce acidic solutions.
For example, aluminium chloride (AlCl3) in water forms Al3+ and Cl- ions. The Al3+ ion reacts with water to form Al(OH)2+ and H+ ions, increasing the H+ concentration in the solution.
This hydrolysis reaction can be written as:
\text{Al\( ^{3+} \) + 3H\(_{2}\)O ↔ Al(OH)\(_{3}\) + 3H}\(^{+}\)

• In general, solutions with high H+ concentration are acidic.

basic solutions

A basic solution has an excess of hydroxide ions (OH-).
When salts undergo anionic hydrolysis, they often produce basic solutions.
For example, sodium carbonate (Na2CO3) in water forms Na+ and CO3^2- ions. The CO3^2- ion reacts with water to form HCO3- and OH- ions, increasing the OH- concentration in the solution.
This hydrolysis reaction can be written as:
\text{CO\(_{3}^{2-}\) + H\(_{2}\)O ↔ HCO\(_{3}^{-}\) + OH}\(^{-}\)

• In general, solutions with high OH- concentration are basic.