The equivalent weight of phosphoric acid `(H_(3)PO_(4))` in the reaction `NaOH+H_(3)PO_(4) rarr NaH_(2)PO_(4)+H_(2)O` is

Options

A. `25`
B. `98`
C. `59`
D. `49`

Explanation

To find the equivalent weight of phosphoric acid (H₃PO₄) in the given reaction, we can follow these steps:

### Step 1: Understand the Reaction
The reaction provided is:
\[ \text{NaOH} + \text{H}_3\text{PO}_4 \rightarrow \text{NaH}_2\text{PO}_4 + \text{H}_2\text{O} \]

In this reaction, phosphoric acid (H₃PO₄) reacts with sodium hydroxide (NaOH) to form sodium dihydrogen phosphate (NaH₂PO₄) and water.

### Step 2: Determine the Change in Valency
Equivalent weight is defined as the molecular weight divided by the change in valency (or valence factor). In acid-base reactions, the valence factor typically corresponds to the number of H⁺ ions that can be donated by the acid.

In this case, H₃PO₄ can donate 1 H⁺ ion when it reacts with NaOH to form NaH₂PO₄. Therefore, the change in valency (valence factor) is 1.

### Step 3: Calculate the Molecular Weight of H₃PO₄
The molecular weight of phosphoric acid (H₃PO₄) can be calculated as follows:
- Hydrogen (H): 1 g/mol × 3 = 3 g/mol
- Phosphorus (P): 31 g/mol × 1 = 31 g/mol
- Oxygen (O): 16 g/mol × 4 = 64 g/mol

Adding these together:
\[ \text{Molecular Weight of H}_3\text{PO}_4 = 3 + 31 + 64 = 98 \text{ g/mol} \]

### Step 4: Calculate the Equivalent Weight
Now we can calculate the equivalent weight using the formula:
\[ \text{Equivalent Weight} = \frac{\text{Molecular Weight}}{\text{Change in Valency}} \]

Substituting the values we have:
\[ \text{Equivalent Weight} = \frac{98 \text{ g/mol}}{1} = 98 \text{ g/equiv} \]

### Conclusion
The equivalent weight of phosphoric acid (H₃PO₄) in the given reaction is **98 g/equiv**.

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