Question

Part A

A mixture of He, Ar, and Xe has a total pressure of 2.70 atm . The partial pressure of He is 0.450 atm , and the partial pressure of Ar is 0.450 atm . What is the partial pressure of Xe?

Express your answer to three significant figures and include the appropriate units.

Part B

A volume of 18.0 L contains a mixture of 0.250 mole N2 , 0.250 mole O2 , and an unknown quantity of He. The temperature of the mixture is 0 ∘C , and the total pressure is 1.00 atm . How many grams of helium are present in the gas mixture?

Express your answer to three significant figures and include the appropriate units.

Answer 1

A)

Use Dalton law of partial pressure:

Ptotal = p(He) + p(Ar) + p(Xe)

2.70 atm = 0.450 atm + 0.450 atm + p(Xe)

p(Xe) = 1.80 atm

Answer: 1.80 atm

B)

1st calculate the total mol of gas.

Given:

P = 1.0 atm

V = 18.0 L

T = 0.0 oC

= (0.0+273) K

= 273 K

find number of moles using:

P * V = n*R*T

1 atm * 18 L = n * 0.08206 atm.L/mol.K * 273 K

n = 0.8035 mol

Now use:

total mol of gas = mol of N2 + mol of O2 + mol of He

0.8035 mol = 0.250 mol + 0.250 mol + mol of He

mol of He = 0.3035 mol

Molar mass of He = 4.003 g/mol

use:

mass of He,

m = number of mol * molar mass

= 0.3035 mol * 4.003 g/mol

= 1.215 g

Answer: 1.22 g