`0.1M HCl` is added to an unknown strength of `NaOH` solution. Identify the correct diagram

Options

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Answer

To solve the problem of identifying the correct pH versus volume graph when adding 0.1M HCl to an unknown strength of NaOH solution, we can follow these steps:

### Step 1: Understand the Reaction
When HCl (a strong acid) is added to NaOH (a strong base), they react to form NaCl (a neutral salt) and water. This neutralization reaction can be represented as:
\[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]

### Step 2: Analyze Initial Conditions
Initially, we have only NaOH in the solution. The pH of a NaOH solution is typically high (around 12-14, depending on its concentration). Therefore, at the start (when no HCl is added), the pH will be at its maximum.

### Step 3: Adding HCl
As we begin to add HCl to the NaOH solution, the pH will start to decrease. This is because the strong acid (HCl) will neutralize the strong base (NaOH).

### Step 4: Determine the Equivalence Point
The equivalence point occurs when all the NaOH has reacted with HCl. At this point, the solution will consist of NaCl and water, and the pH will be neutral (around 7).

### Step 5: Post-Equivalence
After the equivalence point, if more HCl is added, the solution will become acidic, and the pH will drop further below 7.

### Step 6: Sketch the pH vs. Volume Graph
1. Start with a high pH (around 12-14) when only NaOH is present.
2. As HCl is added, the pH will gradually decrease.
3. At the equivalence point, the pH will sharply drop to around 7.
4. After the equivalence point, the pH will continue to decrease as more HCl is added.

### Conclusion
Based on this analysis, the correct graph will show a high initial pH that decreases gradually, then drops sharply at the equivalence point, and continues to decrease as more HCl is added.