A strong acid is titrated with weak base. At equivalence point, pH will be :

Options

A. ` lt 7`
B. `gt 7`
C. 0
D. Cannot predict

Explanation

To determine the pH at the equivalence point when a strong acid is titrated with a weak base, we can follow these steps:

### Step 1: Understand the Reaction
In this titration, we are mixing a strong acid (like HCl) with a weak base (like NH₃). At the equivalence point, all the strong acid will have reacted with the weak base to form a salt (NH₄Cl in this case) and water.

**Hint:** Remember that at the equivalence point, the moles of acid equal the moles of base.

### Step 2: Identify the Products
The reaction between HCl (strong acid) and NH₃ (weak base) produces NH₄⁺ (ammonium ion) and Cl⁻ (chloride ion). The ammonium ion is the conjugate acid of the weak base.

**Hint:** Identify the conjugate acid and base in the reaction.

### Step 3: Analyze the pH
At the equivalence point, the solution contains NH₄⁺ ions. Since NH₄⁺ is a weak acid, it will partially ionize in water to produce H⁺ ions (or hydronium ions, H₃O⁺):

\[ \text{NH}_4^+ + \text{H}_2\text{O} \rightleftharpoons \text{NH}_3 + \text{H}_3\text{O}^+ \]

This reaction increases the concentration of H₃O⁺ ions in the solution, leading to a decrease in pH.

**Hint:** Consider how the conjugate acid behaves in water.

### Step 4: Conclusion on pH
Since the solution now contains an excess of H₃O⁺ ions due to the ionization of NH₄⁺, the pH will be less than 7, indicating that the solution is acidic.

**Hint:** Recall that a pH less than 7 indicates an acidic solution.

### Final Answer
At the equivalence point of titrating a strong acid with a weak base, the pH will be less than 7.