A 1.00-g sample of a gaseous compound of boron and hydrogen occupies 0.820 L at 1.00 atm and 3°C. What is the molecular formula for the compound?

Question

Quizplus · Accepted Answer

First, convert the temperature to Kelvin (K) by adding 273 to the Celsius temperature: 3°C + 273 = 276 K. Use the ideal gas law PV = nRT to find the moles of gas (n). R is the ideal gas constant (0.0821 L·atm/mol·K). n = PV / RT = (1.00 atm)(0.820 L) / (0.0821 L·atm/mol·K)(276 K) ≈ 0.036 mol. The molar mass of the compound is the mass of the sample divided by the number of moles: 1.00 g / 0.036 mol ≈ 27.8 g/mol. The molecular formula that corresponds to a molar mass of approximately 27.8 g/mol is BH3, which is choice A.

A 100-G Sample of a Gaseous Compound of Boron and Hydrogen