0.45 g an acid (mol wt.=90) required 20 ml of 0.5 N KOH for complete neutralization. Basicity of acid is

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To solve the problem step by step, we will determine the basicity of the acid using the given data.

### Step 1: Identify the given data
- Mass of the acid (W_A) = 0.45 g
- Molecular weight of the acid (M) = 90 g/mol
- Volume of KOH solution (V_KOH) = 20 mL = 0.020 L
- Normality of KOH (N_KOH) = 0.5 N

### Step 2: Calculate the number of equivalents of KOH
Normality (N) is defined as the number of equivalents per liter of solution. Therefore, we can calculate the number of equivalents of KOH used:

\[ \text{Number of equivalents of KOH} = N_{KOH} \times V_{KOH} = 0.5 \, \text{N} \times 0.020 \, \text{L} = 0.01 \, \text{equivalents} \]

### Step 3: Determine the equivalent weight of the acid
The equivalent weight (EW) of the acid can be calculated using the formula:

\[ \text{Normality} (N) = \frac{W_B \times 1000}{\text{Equivalent weight} \times V} \]

Rearranging this formula to find the equivalent weight gives:

\[ \text{Equivalent weight} = \frac{W_A \times 1000}{N_{KOH} \times V_{KOH}} \]

Substituting the known values:

\[ \text{Equivalent weight} = \frac{0.45 \, \text{g} \times 1000}{0.5 \, \text{N} \times 20 \, \text{mL}} = \frac{450}{10} = 45 \, \text{g/equiv} \]

### Step 4: Calculate the basicity of the acid
Basicity (b) of the acid is defined as the number of replaceable hydrogen ions (H⁺) per molecule of acid, which can be calculated using the formula:

\[ \text{Basicity} = \frac{\text{Molecular weight}}{\text{Equivalent weight}} \]

Substituting the values:

\[ \text{Basicity} = \frac{90 \, \text{g/mol}}{45 \, \text{g/equiv}} = 2 \]

### Conclusion
The basicity of the acid is 2.