Analyzing Statements about Salts, Acids, and Bases

Let's examine each statement to determine which one is correct regarding salts, acids, and bases.

Statement 1: Hydrolysis of a neutral Salt gives rise to acid and base

Hydrolysis is the reaction of a salt with water. A neutral salt is typically formed from the reaction of a strong acid and a strong base (e.g., \(\text{NaCl}\) from \(\text{HCl}\) and \(\text{NaOH}\)).

• When a neutral salt like \(\text{NaCl}\) dissolves in water, it dissociates into ions (\(\text{Na}^+\) and \(\text{Cl}^-\)).
• These ions come from a strong base (\(\text{NaOH}\)) and a strong acid (\(\text{HCl}\)).
• Ions from strong acids and strong bases do not react significantly with water (they do not undergo hydrolysis) because the conjugate acids and bases formed would be very weak.
• Therefore, the solution remains neutral, not producing significant amounts of separate acid and base compounds.

This statement is incorrect because hydrolysis of a neutral salt results in a neutral solution.

Statement 2: Acid and base reacts to give neutral salt always.

The reaction between an acid and a base is called neutralization, and it typically produces a salt and water:

\(\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}\)

However, the nature of the resulting salt (whether it is acidic, basic, or neutral) depends on the strength of the acid and the base that reacted:

• Strong Acid + Strong Base: Forms a neutral salt (e.g., \(\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}\)).
• Strong Acid + Weak Base: Forms an acidic salt (e.g., \(\text{HCl} + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl}\)).
• Weak Acid + Strong Base: Forms a basic salt (e.g., \(\text{CH}_3\text{COOH} + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O}\)).
• Weak Acid + Weak Base: The salt's nature depends on the relative strengths of the acid and base.

Since the salt formed can be acidic, basic, or neutral, stating that it "always" gives a neutral salt is incorrect.

Statement 3: Citric acid is neutralised by Caustic soda to give neutral salt.

Let's identify the substances:

• Citric acid is a weak acid (\(\text{C}_6\text{H}_8\text{O}_7\)).
• Caustic soda is Sodium Hydroxide (\(\text{NaOH}\)), which is a strong base.

As discussed earlier, the reaction between a weak acid and a strong base produces a basic salt. For example, the reaction of citric acid with \(\text{NaOH}\) can form sodium citrate. Sodium citrate, when dissolved in water, undergoes hydrolysis, making the solution basic.

This statement is incorrect because the reaction between a weak acid (citric acid) and a strong base (caustic soda) produces a basic salt, not a neutral one.

Statement 4: Ammonium Nitrate is an acidic salt.

Let's consider the parent acid and base of Ammonium Nitrate (\(\text{NH}_4\text{NO}_3\)):

• The cation \(\text{NH}_4^+\) comes from Ammonia (\(\text{NH}_3\)), which is a weak base.
• The anion \(\text{NO}_3^-\) comes from Nitric acid (\(\text{HNO}_3\)), which is a strong acid.

A salt formed from a weak base and a strong acid is an acidic salt. The cation from the weak base (\(\text{NH}_4^+\)) undergoes hydrolysis in water:

\(\text{NH}_4^+(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{NH}_3(aq) + \text{H}_3\text{O}^+(aq)\)

This hydrolysis reaction produces hydronium ions (\(\text{H}_3\text{O}^+\)), increasing the acidity of the solution. Therefore, Ammonium Nitrate is indeed an acidic salt.

This statement is correct.

Conclusion

Based on the analysis of each statement, the only correct statement is that Ammonium Nitrate is an acidic salt.