Chemistry Gas Law

Question

1) What is the mass of 4 L of water vapor at 120◦C and 396 torr?

Answer 1

Pressure (P) = 396 torr x 1 atm/760 torr = 0.521 atm

Volume (V) = 4 L

Temperature (T) = 120ºC + 273 = 393K

n = moles = ?

Assuming water vapor behaves ideally, and using the ideal gas law PV = nRT and solving for n, we have...

n = PV/RT = (0.521 atm)(4 L)/(0.0821 Latm/Kmol)(393K)

n = 0.0646 moles H2O vapor

mass = 0.0646 moles x 18 g/mole = 1.16 g