Question

(g) The mole fraction of O2 in atmospheric air is 0.21. Calculate the concentration of O2 in a sample of atmospheric air in a 10 L container at a pressure of 650 mmHg and temperature of 160 °C.

Answer 1

Answer:

The concentration of O₂ in the sample is 5,1x10⁻³ M (mol/L)

Explanation:

To obtain the moles of gas you should use ideal gas formula:

PV/RT = n

Where:

P is pressure: 650 mmHg or 650 mmHg* ( 1 atm / 760 mmHg) = 0,855 atm

V is volume: 10 L

R is gas constant: 0,082 atm·L/mol·K

T is temperature: 160°C or 160 + 273,15 = 433,15 K

And n is mol number

Thus, replacing bold values in ideal gas formula:

n =  0,24 mol

The mole fraction of O₂ in atmospheric air is 0,21. Thus, the moles of O₂ there are:

0,24 moles of atmospheric air ₓ 0,21 = 0,051 O₂ moles

There are many ways to express concentration but we will express it in molarity (mol of solute / L of solution) understanding solute as O₂ and solution as atmospheric air. So:

0,051 O₂ moles / 10 L = 5,1x10⁻³ M -M is molarity-

I hope it helps!