5 L of gas at STP weight 6.25 g . What is the gram molecular weight ?

Options

A. 1.25
B. 14
C. 28
D. 56

Answer

To find the gram molecular weight (molar mass) of the gas, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Information:**
- Volume of gas = 5 L
- Weight of gas = 6.25 g
- Standard Temperature and Pressure (STP) conditions imply that 1 mole of gas occupies 22.4 L.

2. **Calculate the Weight of 1 L of Gas:**
- Weight of 1 L of gas = Total weight of gas / Volume of gas
- Weight of 1 L = 6.25 g / 5 L = 1.25 g/L

3. **Relate the Weight of 1 L of Gas to Molar Mass:**
- At STP, 1 mole of gas occupies 22.4 L. Therefore, the weight of 1 mole of gas (molar mass, M) can be expressed as:
- Weight of 1 L of gas = M / 22.4 L
- Rearranging gives us M = Weight of 1 L × 22.4 L

4. **Substitute the Weight of 1 L into the Equation:**
- M = 1.25 g/L × 22.4 L

5. **Calculate the Molar Mass:**
- M = 1.25 × 22.4 = 28 g/mol

6. **Conclusion:**
- The gram molecular weight (molar mass) of the gas is 28 g/mol.

### Final Answer:
The gram molecular weight of the gas is **28 g/mol**.