10.78 g of `H_3 PO_4` in 550 ml solution is 0.40 N. Thus this acid:

Options

A. has been neutralized to `HPO_(4)^(2-)`
B. has been neutralized to `PO_(4)^(3-)`
C. has been reduced to `HPO_(3)^(2-)`
D. has been neutralized to `H_2 PO_(4)^(-)`

Answer

To solve the problem, we need to determine the species that phosphoric acid (H₃PO₄) can neutralize or reduce to, given the provided data.

### Step-by-Step Solution:

1. **Identify the Given Data**:
- Mass of H₃PO₄ = 10.78 g
- Volume of solution = 550 ml = 0.550 L
- Normality (N) = 0.40 N

2. **Use the Normality Formula**:
The formula for normality is given by:
\[ N = \frac{\text{Given Weight}}{\text{Equivalent Weight} \times \text{Volume in Liters}} \]
Rearranging this formula to find the equivalent weight:
\[ \text{Equivalent Weight} = \frac{\text{Given Weight}}{N \times \text{Volume in Liters}} \]

3. **Calculate the Equivalent Weight**:
Substitute the values into the formula:
\[ \text{Equivalent Weight} = \frac{10.78 \, \text{g}}{0.40 \times 0.550} \]
Calculating this gives:
\[ \text{Equivalent Weight} = \frac{10.78}{0.22} = 49 \, \text{g/equiv} \]

4. **Determine the Molecular Weight of H₃PO₄**:
The molecular weight of H₃PO₄ can be calculated as follows:
- H: 1 g/mol × 3 = 3 g/mol
- P: 31 g/mol
- O: 16 g/mol × 4 = 64 g/mol
\[ \text{Molecular Weight} = 3 + 31 + 64 = 98 \, \text{g/mol} \]

5. **Calculate the n-factor**:
The equivalent weight is also related to the molecular weight and the n-factor:
\[ \text{Equivalent Weight} = \frac{\text{Molecular Weight}}{\text{n-factor}} \]
Rearranging gives:
\[ \text{n-factor} = \frac{\text{Molecular Weight}}{\text{Equivalent Weight}} = \frac{98}{49} = 2 \]

6. **Interpret the n-factor**:
The n-factor of 2 indicates that H₃PO₄ can donate 2 protons (H⁺ ions) in a reaction. This means that it is a dibasic acid.

7. **Identify the Species Formed**:
- When H₃PO₄ donates 2 protons, it can form HPO₄²⁻ (dihydrogen phosphate ion).
- It can also be reduced to HPO₃²⁻ (phosphite ion) by losing additional protons or through redox reactions.

### Conclusion:
From the calculations, we conclude that H₃PO₄ can neutralize to HPO₄²⁻ and can be reduced to HPO₃²⁻.