Question

calculate the number of moles of H2 gas collected over water that filled a graduated cylinder with 75.2 ml of gas at a temp perature of 19C and an atmospheric pressure of 749 torr. The vapor pressure of water at 19C = 16.48 torr. R = 62.363
I got .00309 mol H2, but missed one point on this question. Not sure what I did wrong. Will someone help me step by step, please? Thank you so much.

Answer 1

First we need to know the pressure of just the hydrogen gas. To find that, subtract the vapor pressure from the total pressure:
(749torr-16.48torr) = 732.52torr H2 gas

Now use the ideal gas law to find moles of H2 gas:
n= PV/RT
(732.52torr)(.0752L)/(62.63)(292K) = 0.003mol H2
:)