Question

The correct statement is (1) \(\mathrm{NII}_{4} \mathrm{Cl}\) gives an alkalinc solution in water (2) \(\mathrm{CII}_{3}\) COONa gives an acidic solution in water (3) \(\mathrm{CII}_{3} \mathrm{COOII}\) is a weak acid (4) \(\mathrm{NII}_{4} \mathrm{OII}\) is a strong base

Short answer

(3) \(\text{CH}_3\text{COOH}\) is a weak acid.

Step-by-step solution

- Evaluate \(\text{NH}_4\text{Cl}\)

\text{NH}_4\text{Cl} is formed from a strong acid (HCl) and a weak base (NH_3). In water, it dissociates into \(\text{NH}_4^+\) and \(\text{Cl}^-\). \(\text{NH}_4^+\) will dissociate to form \(\text{NH}_3 + \text{H}^+\), resulting in an acidic solution, not alkaline.

- Evaluate \(\text{CH}_3\text{COONa}\)

\text{CH}_3\text{COONa} is formed from a weak acid (CH_3COOH) and a strong base (NaOH). In water, it dissociates into \(\text{CH}_3\text{COO}^-\) and \(\text{Na}^+\). \(\text{CH}_3\text{COO}^-\) hydrolyzes to form \(\text{CH}_3\text{COOH} + \text{OH}^-\), resulting in a basic solution.

- Evaluate \(\text{CH}_3\text{COOH}\)

\text{CH}_3\text{COOH} is acetic acid, a well-known weak acid. Thus, the statement \(\text{CH}_3\text{COOH}\) is a weak acid is correct.

- Evaluate \(\text{NaOH}\)

\text{NaOH} is a strong base, and there is no compound known as \(\text{NH}_4\text{OH}\) being called a strong base. \(\text{NH}_4^{2+}\) is not a valid ion for a base. The correct strong base mentioned here would be NaOH.

Key concepts

Strong acids and bases

Strong acids and bases fully dissociate in water. This means they break apart completely into ions.
Examples of strong acids include HCl (hydrochloric acid) and HNO₃ (nitric acid).
Strong bases, like NaOH (sodium hydroxide) and KOH (potassium hydroxide), also dissociate completely.
For instance, NaOH dissociates into Na⁺ and OH^-.
Because of this complete dissociation, strong acids and bases conduct electricity well and have drastic pH changes upon dilution.

Weak acids and bases

Weak acids and bases only partially dissociate in water.
This incomplete dissociation means that not all of the acid or base molecules break into ions.
An example of a weak acid is acetic acid (CH₃COOH).
In water, acetic acid partially dissociates into H⁺ and CH₃COO^-.
On the other hand, weak bases like NH₃ (ammonia) partially ionize to form NH₄⁺ and OH^-.
As a result, solutions of weak acids and bases have a moderate pH and show less conductivity compared to their strong counterparts.

Salt hydrolysis

Salt hydrolysis occurs when a salt formed from a strong acid and a weak base (or vice versa) reacts with water, affecting the solution's pH.
For example, NH₄Cl is formed from the strong acid HCl and the weak base NH₃.
When NH₄Cl dissolves in water, it dissociates into NH₄⁺ and Cl^-.
NH₄⁺ can release H⁺ ions, making the solution acidic.
Conversely, CH₃COONa is formed from the weak acid CH₃COOH and the strong base NaOH.
It dissociates into CH₃COO^- and Na⁺.
CH₃COO^- can accept H⁺ ions, making the solution basic.

Acidic and basic solutions

Solutions can be classified as acidic or basic based on their pH levels.
Acidic solutions have a pH less than 7 and contain a higher concentration of H⁺ ions.
Examples include vinegar (which contains acetic acid) and lemon juice (which contains citric acid).
Basic solutions have a pH greater than 7 and contain a higher concentration of OH^- ions.
Examples include baking soda solution (which contains sodium bicarbonate) and soap solution.
The pH scale ranges from 0 to 14, with 7 being neutral (like pure water).
Understanding the nature of acids, bases, and salts can help predict whether a solution will be acidic or basic.