Question

A) What mass of carbon dioxide is present in 1.00 m3 of dry air at a temperature of 17 ∘C and a pressure of 695 torr ?

B) Calculate the mass percentage of oxygen in dry air.

Answer 1

Assume comopsition of CO2 is constant for dry air, so:

0.04% by mole ---> 0.04/100 = 0.0004 (fraction)

Density of air:

D = P*MW/(RT)

D = (695/760)(29)/(0.082*(17+273))

D = 1.11521 g/mL

in 1 m3 = 1000 L

so

Mass = D*V = 1.11521*1000 = 1115.21 g of air

we know that 0.0004 is CO2 --> 0.0004 *1115.21 = 0.446084 g of CO2

B)

mass of O2 in dry air

Dry air will have 20.9 mol of O2 of O2 per 100 mol of Air

so...

MW of Air = 29 g/mol

MW of O2 = 32 g/mol

mass of O2 = 20.9 *32 = 668.8 g of O2

mass of air = 29*100 = 2900 g

mass frac = O2 / total mass = 668.8 / 2900 = 0.230620

%O2 = 0.230620*100% = 23.06% by mass