Question

a sample of oxygen is collected over water at a total pressure of 1.08atm at 30° C the vapor pressure of water at 31.82 mmHg. How many moles of oxygen are present if the volume of the gases is 775 mL?

Answer 1

pH2O = 31.82 mmHg

pH2O = 31.82/760 atm

pH2O = 0.0419 atm

pO2 = ptotal - pH2O

= 1.08 atm - 0.0419 atm

= 1.038 atm

we have:

P = 1.038 atm

V = 775.0 mL

= (775.0/1000) L

= 0.775 L

T = 30.0 oC

= (30.0+273) K

= 303 K

find number of moles using:

P * V = n*R*T

1.038 atm * 0.775 L = n * 0.08206 atm.L/mol.K * 303 K

n = 3.23*10^-2 mol

Answer: 3.23*10^-2 mol