Which of the following plot represents the graph of pH against volume of alkali added in the titration of NaOH and HCl

Options

A.
B.
C.
D.

Answer

To determine which plot represents the graph of pH against the volume of alkali added in the titration of NaOH and HCl, we need to understand the behavior of pH during this titration process.

### Step-by-Step Solution:

1. **Identify the Reaction**:
- The titration involves a strong acid (HCl) and a strong base (NaOH). The reaction can be represented as:
\[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]

2. **Understand the pH Scale**:
- The pH scale ranges from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic.

3. **Initial pH of HCl**:
- Before any NaOH is added, the solution is acidic due to HCl. The pH will be less than 7, typically around 1-3 depending on the concentration of HCl.

4. **Adding NaOH**:
- As NaOH is gradually added, the pH will start to increase. Initially, the pH will rise slowly as the acid is neutralized.

5. **Equivalence Point**:
- At the equivalence point, where all the HCl has reacted with NaOH, the solution will be neutral, and the pH will be around 7.

6. **Post-Equivalence**:
- After the equivalence point, adding more NaOH will cause the pH to rise sharply above 7, indicating a basic solution.

7. **Graph Characteristics**:
- The graph of pH versus the volume of NaOH added will show a gradual increase in pH at first, followed by a steep rise around the equivalence point (pH = 7), and then a leveling off as more NaOH is added.

8. **Identifying the Correct Plot**:
- The correct plot will show a sharp increase in pH around the volume where the equivalence point occurs (between pH 4 and 7). It should not show a gradual slope throughout but rather a steep rise indicating the transition from acidic to neutral to basic.

### Conclusion:
- The third option is the correct representation of the graph, as it shows the steep increase in pH around the equivalence point, indicating the transition from acidic to neutral to basic.