0.1 mol of an acidic substance P requires `25 cm^(3)` of `8.0 "mol/dm"^(3)` sodium hydroxide for complete neutralisation P could be

Options

A. Hydrochloric acid
B. Sulphuric acid
C. Acetic acid
D. Phosphoric acid.

Answer

To solve the problem, we need to determine which acidic substance P corresponds to the given neutralization reaction with sodium hydroxide (NaOH). We know that 0.1 moles of substance P requires 25 cm³ of 8.0 mol/dm³ NaOH for complete neutralization.

### Step-by-step Solution:

1. **Calculate the moles of NaOH used**:
- First, we convert the volume of NaOH from cm³ to dm³:
\[ 25 \, \text{cm}^3 = 25 \times 0.001 \, \text{dm}^3 = 0.025 \, \text{dm}^3 \]
- Now, we can calculate the moles of NaOH using the formula:
\[ \text{Moles of NaOH} = \text{Molarity} \times \text{Volume} = 8.0 \, \text{mol/dm}^3 \times 0.025 \, \text{dm}^3 = 0.2 \, \text{mol} \]

2. **Determine the ratio of moles of acid to base**:
- We have 0.1 moles of acidic substance P and 0.2 moles of NaOH.
- The ratio of moles of P to NaOH is:
\[ \text{Ratio} = \frac{0.1 \, \text{mol}}{0.2 \, \text{mol}} = \frac{1}{2} \]

3. **Identify the possible acidic substances**:
- We need to find an acid that reacts with NaOH in a 1:2 ratio. The candidates are:
- Hydrochloric acid (HCl): reacts in a 1:1 ratio.
- Sulfuric acid (H₂SO₄): reacts in a 1:2 ratio.
- Acetic acid (CH₃COOH): reacts in a 1:1 ratio.
- Phosphoric acid (H₃PO₄): reacts in a 1:3 ratio.

4. **Conclusion**:
- The only acid that fits the 1:2 ratio with NaOH is sulfuric acid (H₂SO₄).

Thus, the acidic substance P could be **sulfuric acid (H₂SO₄)**.