What is the mass of 3 L of water vapor at 120◦C and 388 torr?

Use gas equation to calculate mol of H2O gas:

P = pressure = 389/760 = 0.512atm

V = volume = 4L

n=?

R = 0.082057

T = 121+273 = 394K

0.512 * 4 = n*0.082057*394

n = (0.512*4) / (0.082057*394)

n = 2.048 / 32.33

n = 0.063 mol H2O

Molar5 mass H2O = 18g/mol

Mass of water = 0.063*18

Mass of water valour = 1.14g