Two gases A and B have molecular weight 60 and 45. 0.6 g of A and 0.9 g of B are mixed in a closed vessel. Total pressure is 720 mm. The partial pressure of A is

Options

A. 240 mm
B. 480 mm
C. 600 mm
D. None of these

Explanation

To find the partial pressure of gas A in a mixture of two gases A and B, we can follow these steps:

### Step 1: Calculate the number of moles of gas A
The formula to calculate the number of moles is:
\[ \text{Number of moles} = \frac{\text{Mass}}{\text{Molar mass}} \]
For gas A:
- Mass of A = 0.6 g
- Molar mass of A = 60 g/mol

Calculating the moles of A:
\[ \text{Moles of A} = \frac{0.6 \, \text{g}}{60 \, \text{g/mol}} = 0.01 \, \text{moles} \]

### Step 2: Calculate the number of moles of gas B
Using the same formula for gas B:
- Mass of B = 0.9 g
- Molar mass of B = 45 g/mol

Calculating the moles of B:
\[ \text{Moles of B} = \frac{0.9 \, \text{g}}{45 \, \text{g/mol}} = 0.02 \, \text{moles} \]

### Step 3: Calculate the total number of moles in the mixture
Now, we can find the total number of moles by adding the moles of A and B:
\[ \text{Total moles} = \text{Moles of A} + \text{Moles of B} = 0.01 + 0.02 = 0.03 \, \text{moles} \]

### Step 4: Calculate the mole fraction of gas A
The mole fraction (X) of gas A is given by:
\[ X_A = \frac{\text{Moles of A}}{\text{Total moles}} = \frac{0.01}{0.03} = \frac{1}{3} \]

### Step 5: Calculate the partial pressure of gas A
Using Dalton's Law of Partial Pressures, the partial pressure of gas A can be calculated using the formula:
\[ P_A = X_A \times P_{\text{total}} \]
Where:
- \(P_{\text{total}} = 720 \, \text{mm Hg}\)

Calculating the partial pressure of A:
\[ P_A = \frac{1}{3} \times 720 \, \text{mm Hg} = 240 \, \text{mm Hg} \]

### Final Answer
The partial pressure of gas A is **240 mm Hg**.

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