Question

The mass of 322 mL of hydrogen gas at 4.0 atm and –73°C is 1.21 grams. What is the density of hydrogen gas at STP?
6.88 × 10–4 g/mL
4.87 X 101
1.45 × 103 g/mL
1.28 × 10–3 g/mL

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Answer 1

To be able to answer this item, we assume that the given hydrogen gas is ideal such that we are able to use the Ideal Gas equation,
                               PV = nRT
At STP, the values of volume, pressure, and temperature are 22.4 L, 1 atm, and 273.15 K. Solving for n,
                              n = (1 atm x 22.4 L) / (0.0821 L.atm/mol K x 273.15 K)
                                                  n = 0.9988 mols
Each mol of hydrogen gas is 2 g.
                                                 m = (0.9988 mols) x (2 g/1 mol)
                                                   m = 1.9977 g
Density is the quotient of mass and volume,
                           density = 1.9977 g/ 22400 mL
                            density = 8.92 x 10^-5 g/mL