Which of the following statements about a weak acid strong base titration is//are correct?

Options

A. The `pH` after the equivalence point of the weal acid string base titration is determined by using the `K_(b)` expression for the conjugate base.
B. A buffer solution of weal acid and its conjugate base is formed before the equivalence is reached.
C. The `pH` at the equivalence point of a weak monoprotic acid strong base titration is equal to the `pH` at the equivalence point of a strong acid-strong base titration.
D. The increase in `pH` in the region near the equivalence point of a weak acid strong base titration is grater than the `pH` change in the same region of a strong acid strong base titration

Answer

To determine which statements about a weak acid-strong base titration are correct, we can analyze each statement one by one:

### Step 1: Analyze the First Statement
**Statement:** "pH after the equivalence point of the weak acid and strong base titration is determined by using the KB expression for the conjugate base."

**Analysis:**
At the equivalence point of a weak acid-strong base titration, all the weak acid has been neutralized by the strong base, resulting in the formation of the conjugate base of the weak acid. The pH after the equivalence point is influenced by this conjugate base, which can hydrolyze in water to produce hydroxide ions (OH⁻). Therefore, to calculate the pH, we use the KB expression for the conjugate base.

**Conclusion:** This statement is correct.

### Step 2: Analyze the Second Statement
**Statement:** "A buffer solution of weak acid and its conjugate base is formed before the equivalence point is reached."

**Analysis:**
Before reaching the equivalence point, there will be a mixture of the weak acid and its salt (formed from the weak acid and the strong base). This combination creates a buffer solution, which can resist changes in pH upon the addition of small amounts of acid or base.

**Conclusion:** This statement is also correct.

### Step 3: Analyze the Third Statement
**Statement:** "The pH at the equivalence point of a weak monoprotic acid and strong base titration is equal to the pH of a strong acid and strong base titration."

**Analysis:**
In a strong acid-strong base titration, the resulting solution is neutral, leading to a pH of 7 at the equivalence point. However, in a weak acid-strong base titration, the resulting solution contains the conjugate base of the weak acid, which makes the solution basic. Therefore, the pH at the equivalence point of a weak acid-strong base titration is greater than 7.

**Conclusion:** This statement is incorrect.

### Step 4: Analyze the Fourth Statement
**Statement:** "The increase in pH in the region near the equivalence point of a weak acid-strong base titration is greater than the pH change in the region of strong acid and strong base."

**Analysis:**
In a weak acid-strong base titration, the pH changes gradually until the equivalence point is reached, where it may change rapidly. However, in a strong acid-strong base titration, the pH changes significantly as the equivalence point is approached. The buffer region in the weak acid-strong base titration means that the pH does not change as dramatically as in the strong acid-strong base titration.

**Conclusion:** This statement is incorrect.

### Final Conclusion
The correct statements about a weak acid-strong base titration are:
1. The first statement is correct.
2. The second statement is correct.
3. The third statement is incorrect.
4. The fourth statement is incorrect.

### Summary of Correct Statements
- **Correct Statements:** 1 and 2.
- **Incorrect Statements:** 3 and 4.