A sample of hydrogen gas was collected by displacement of water in a large gas buret. The total pressure in the buret was measured as 764.2 torr, the temperature was 23.0 °C, and the buret contained 511 mL of the collected gas. How many moles of hydrogen were collected?(At 23.0 °C, the vapor pressure of water is 21.1 torr.)

Question

Quizplus · Accepted Answer

To find the moles of hydrogen, first subtract the vapor pressure of water from the total pressure to get the pressure of hydrogen: 764.2 torr - 21.1 torr = 743.1 torr. Convert this pressure to atm: 743.1 torr / 760 torr/atm = 0.977 atm. Convert the volume to liters: 511 mL = 0.511 L. Use the ideal gas law: PV = nRT, where R = 0.0821 L·atm/mol·K and T = 23.0 °C = 296.15 K. Solving for n gives n = PV / RT = (0.977 atm)(0.511 L) / (0.0821 L·atm/mol·K)(296.15 K) = 0.0206 moles.

A Sample of Hydrogen Gas Was Collected by Displacement of Water