18. The density of a gas is 1.43 g/L at STP. What is the molar mass of the gas?

1. Write the formula for density:
\rho = \frac{m}{V}

2. Rearrange the formula to solve for mass \( m \):
m = \rho \cdot V

3. Substitute the given values (density \(\rho = 1.43 \, \text{g/L}\) and volume \(V = 22.4 \, \text{L}\)):
m = 1.43 \, \text{g/L} \times 22.4 \, \text{L}

4. Calculate the mass:
m = 32.032 \, \text{g}

5. Since \(1 \, \text{mol}\) of the gas at STP occupies \(22.4 \, \text{L}\), the mass of \(1 \, \text{mol}\) of the gas is \(32.032 \, \text{g}\).

6. Thus, the molar mass \( M \) of the gas is:
M = 32.032 \, \text{g/mol}

So, the final answer is:
M = 32.032 \, \text{g/mol}