Question

A sample of N2(g) was collected over water at 25°C and 730 torr in a container with a volume of 340 mL. The vapor pressure of water at 25°C is 23.76 torr. What mass of N2 was collected?
A. 0.58 g
B. 0.72 g
C. 0.91 g
D. 0.36 g
E. 0.080 g

Answer 1

Answer:

D. 0.36 g

Explanation:

When a gas is collected over water, the total pressure is the sum of the pressure of the gas and the pressure of the water vapor.

Ptotal = Pwater + PN₂

PN₂ = Ptotal - Pwater = 730 torr - 23.76 torr = 706 torr

We can find the mass of N₂ using the ideal gas equation.

$P.V=n.R.T=\frac{m}{M} .R.T\\m=\frac{P.V.M}{R.T} =\frac{730torr.0.340L.28g/mol}{(0.08206atm.L/mol.K).298K} .\frac{1atm}{760torr} =0.36g$