Which of the following graphs shows the change in pH when zinc carbonate is added to hydrochloric acid until it is excess ?

Options

A.
B.
C.
D.

Explanation

To solve the question regarding the change in pH when zinc carbonate (ZnCO3) is added to hydrochloric acid (HCl) until it is in excess, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- When zinc carbonate (ZnCO3) is added to hydrochloric acid (HCl), a chemical reaction occurs. The reaction can be represented as:
\[ \text{ZnCO}_3 + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2\text{O} + \text{CO}_2 \]
- This reaction produces zinc chloride (ZnCl2), water (H2O), and carbon dioxide (CO2).

2. **Initial pH of HCl**:
- Hydrochloric acid is a strong acid, and its pH is typically less than 7. Therefore, the initial pH of the solution will be low (acidic).

3. **Adding Zinc Carbonate**:
- As ZnCO3 is added to the HCl solution, it will start to neutralize the acid. This means the pH will begin to increase as the acid is consumed.

4. **Neutralization Point**:
- The pH will continue to rise until all the HCl is neutralized. At this point, the solution will be neutral (pH = 7).

5. **Excess Zinc Carbonate**:
- Once all the HCl is neutralized, if more ZnCO3 is added, the solution will contain excess ZnCO3. Since ZnCO3 is a salt formed from a weak acid (carbonic acid, H2CO3) and a weak base (zinc hydroxide), the pH will stabilize and not exceed 7 significantly.

6. **Graph Interpretation**:
- The graph showing the change in pH will initially rise as ZnCO3 is added and will plateau at around pH 7 when the acid is neutralized. After that, with excess ZnCO3, the pH will not increase significantly and will remain constant.

7. **Choosing the Correct Graph**:
- Based on the above analysis, the correct graph would show an initial increase in pH followed by a plateau at around pH 7, indicating that the pH does not increase significantly beyond this point with excess ZnCO3.

### Conclusion:
The correct option is the graph that shows the pH increasing to around 7 and then remaining constant.