Question

A sample of H2 is collected by displacing 145 mL of water. The pressures of the gas and the atmosphere are equalized. The atmospheric pressure is 745 mmHg. The temperature of the water and gas are identical at 26 degrees C. How many moles of H2 have been evolved?

Answer 1

First, get the water vapor pressure at 26C. Subtract that water partial pressure from the pressure in the tube, and you have the pressure of H2, you are given the temp, and the volume.

use n=PV/RT to get moles.