Question

What is the volume (in $\text{dm}^3$) occupied by 75 g ethane at S.T.P. ?

• A. 60.0
• B. 56.0
• C. 22.4
• D. 44.8

Hint:

Remember the metric equivalencies! 1 Liter (L) is exactly identical in volume to 1 cubic decimeter ($\text{dm}^3$). Don't let the different units trick you into performing unnecessary conversions.

Answer 1

The Correct Option is B

Step 1: Find the moles of ethane.
Ethane $\text{C}_2\text{H}_6$ has molar mass $30\ \text{g/mol}$. So $n = \dfrac{75}{30} = 2.5\ \text{mol}$.

Step 2: Use molar volume at STP.
At STP one mole of any gas takes up $22.4\ \text{dm}^3$.

Step 3: Multiply.
$$V = 2.5 \times 22.4 = 56.0\ \text{dm}^3$$
\[ \boxed{56.0\ \text{dm}^3} \]