Acid Identification

Acids are substances that donate protons (H⁺ ions) when dissolved in water. They can be classified as either strong acids or weak acids based on their degree of dissociation in water.

• Strong Acids: These acids dissociate almost completely in water, releasing a high concentration of H⁺ ions.
• Weak Acids: These acids dissociate only partially in water, releasing a lower concentration of H⁺ ions compared to strong acids of the same concentration.

Analyzing Acid Options

Let's examine each option provided in the question:

1. $\text{HCl}$ (Hydrochloric Acid): Hydrochloric acid is a common strong acid. It dissociates extensively in water according to the reaction: $\text{HCl(aq)} \rightarrow \text{H}^+\text{(aq)} + \text{Cl}^-\text{(aq)}$.
2. $\text{HNO}_3$ (Nitric Acid): Nitric acid is also a strong acid. It undergoes nearly complete dissociation in water: $\text{HNO}_3\text{(aq)} \rightarrow \text{H}^+\text{(aq)} + \text{NO}_3^-\text{(aq)}$.
3. $\text{CH}_3\text{COOH}$ (Acetic Acid): Acetic acid is the main component of vinegar. It is a weak acid because it only partially dissociates in water. The equilibrium reaction is: $\text{CH}_3\text{COOH(aq)} \rightleftharpoons \text{H}^+\text{(aq)} + \text{CH}_3\text{COO}^-\text{(aq)}$.
4. $\text{H}_2\text{SO}_4$ (Sulfuric Acid): Sulfuric acid is a strong acid, particularly for its first dissociation step. The first dissociation is nearly complete: $\text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{H}^+\text{(aq)} + \text{HSO}_4^-\text{(aq)}$. The second dissociation of $\text{HSO}_4^-$ is weaker, but overall, $\text{H}_2\text{SO}_4$ is considered a strong acid.

Weak Acid Identification

Based on the classifications, $\text{HCl}$, $\text{HNO}_3$, and $\text{H}_2\text{SO}_4$ are all strong acids. Acetic acid ($\text{CH}_3\text{COOH}$) is the only weak acid among the given options. Its partial dissociation in water is characteristic of a weak acid.

Therefore, the weak acid among the given options is $\text{CH}_3\text{COOH}$.