Question

# Part A A mixture of He, Ar, and Xe has a total pressure of 2.90 atm...

Part A

A mixture of He, Ar, and Xe has a total pressure of 2.90 atm . The partial pressure of He is 0.450 atm , and the partial pressure of Ar is 0.250 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.

A)

Use Dalton Laws of partial pressure

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

2.90 atm = 0.450 atm + 0.250 atm + p(Xe)

p(Xe) = 2.20 atm

B)

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:

Mol of He = total mol - mol of N2 - mol of O2

= 0.8035 mol - 0.250 mol - 0.250 mol

= 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

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