What is the mass of 8.55 L of phosphine gas (PH_3) at STP? Round your answer to 3 significant figures.

• A. 11.0 g
• B. 8.55 g
• C. 3.84 g
• D. 13.2 g

Answer: (D)

Verified step by step guidance

1. Identify the given information: volume of phosphine gas (PH\_3) is 8.55 L, and the conditions are at STP (Standard Temperature and Pressure). At STP, 1 mole of any ideal gas occupies 22.4 L.
2. Calculate the number of moles of PH\_3 gas using the formula: \(\text{moles} = \frac{\text{volume}}{\text{molar volume at STP}} = \frac{8.55\, \text{L}}{22.4\, \text{L/mol}}\).
3. Determine the molar mass of phosphine (PH\_3) by adding the atomic masses: Phosphorus (P) is approximately 30.97 g/mol and Hydrogen (H) is approximately 1.008 g/mol. So, \(\text{molar mass} = 30.97 + 3 \times 1.008\) g/mol.
4. Calculate the mass of the phosphine gas using the formula: \(\text{mass} = \text{moles} \times \text{molar mass}\).
5. Round the final mass to 3 significant figures as requested.