Two formulal to calculate number of milli equivalkents (mlQ)
Numbr of miliequivalents `=("weight")/("GEW")xx1000`
Numbr of milliequivalents= volume in ml `xx` Normality of solution
0.09 grams of dibasic acid neutralise 40 ml of `N/20` NaOH solution. Molecular weight of acid is

Options

A. 90
B. 45
C. 180
D. 60

Answer

To find the molecular weight of the dibasic acid that neutralizes a given volume of NaOH solution, we can follow these steps:

### Step 1: Understand the given information
- We have 0.09 grams of a dibasic acid.
- It neutralizes 40 mL of N/20 NaOH solution.
- The acid is dibasic, meaning it can donate 2 protons (H⁺ ions).

### Step 2: Determine the normality of the NaOH solution
- The normality (N) of the NaOH solution is given as N/20.
- Normality can be expressed as:
\[ N = \frac{1}{20} \text{ N} \]

### Step 3: Calculate the number of milliequivalents of NaOH
Using the formula for milliequivalents:
\[ \text{Number of milliequivalents} = \text{Volume (mL)} \times \text{Normality} \]
Substituting the known values:
\[ \text{Number of milliequivalents of NaOH} = 40 \, \text{mL} \times \frac{1}{20} \, \text{N} = 2 \, \text{milliequivalents} \]

### Step 4: Relate the milliequivalents of acid to the milliequivalents of NaOH
Since the acid and base neutralize each other, the number of milliequivalents of acid will equal the number of milliequivalents of NaOH:
\[ \text{Number of milliequivalents of acid} = 2 \, \text{milliequivalents} \]

### Step 5: Use the formula for milliequivalents of the acid
The formula for calculating milliequivalents of the acid is:
\[ \text{Number of milliequivalents} = \frac{\text{Weight (g)}}{\text{Gram Equivalent Weight (GEW)}} \times 1000 \]
For a dibasic acid, the GEW is given by:
\[ \text{GEW} = \frac{\text{Molecular Weight (M)}}{n} \]
where \( n = 2 \) for dibasic acids. Thus,
\[ \text{GEW} = \frac{M}{2} \]

### Step 6: Substitute into the milliequivalents formula
Substituting the values into the milliequivalents formula:
\[ 2 = \frac{0.09}{\frac{M}{2}} \times 1000 \]
This simplifies to:
\[ 2 = \frac{0.09 \times 2000}{M} \]
\[ 2M = 0.09 \times 2000 \]
\[ 2M = 180 \]
\[ M = 90 \]

### Conclusion
The molecular weight of the dibasic acid is **90 g/mol**.

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