What mass of `H_(2)C_(2)O_(4). 2H_(2)O (mol.mass=126)` should be dissoved in water to prepare 250mL of centinormal solution which act as a reducing agent?

Options

A. 0.63g
B. 0.1575g
C. 0.126g
D. 0.875g

Answer

To find the mass of `H2C2O4.2H2O` (oxalic acid dihydrate) needed to prepare a 250 mL centinormal solution, we can follow these steps:

### Step 1: Understand the term "centinormal"
A centinormal solution has a normality of \( \frac{1}{100} \) N. This means that 1 L of the solution contains 0.01 equivalents of the solute.

### Step 2: Calculate the number of equivalents
For a 250 mL solution:
\[ \text{Normality (N)} = \frac{\text{Number of equivalents}}{\text{Volume in L}} \]
Given that the volume is 250 mL (or 0.250 L):
\[ \text{Number of equivalents} = \text{Normality} \times \text{Volume in L} = \frac{1}{100} \times 0.250 = 0.0025 \text{ equivalents} \]

### Step 3: Determine the valency factor (n-factor)
Oxalic acid (`H2C2O4`) acts as a reducing agent and has a valency factor of 2 because it can donate 2 electrons per molecule during the redox reaction.

### Step 4: Calculate the number of moles
Using the relationship between equivalents, moles, and valency factor:
\[ \text{Number of equivalents} = \text{Number of moles} \times n \]
Rearranging gives:
\[ \text{Number of moles} = \frac{\text{Number of equivalents}}{n} = \frac{0.0025}{2} = 0.00125 \text{ moles} \]

### Step 5: Calculate the mass of `H2C2O4.2H2O`
Using the molar mass (given as 126 g/mol):
\[ \text{Mass} = \text{Number of moles} \times \text{Molar mass} = 0.00125 \text{ moles} \times 126 \text{ g/mol} = 0.1575 \text{ grams} \]

### Conclusion
The mass of `H2C2O4.2H2O` that should be dissolved in water to prepare 250 mL of a centinormal solution is **0.1575 grams**.

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