Question

Question one: Assume that dry air consists of only 20.00% oxygen and 80.00% nitrogen by volume.

What is the density of dry air at 0.90030 atm and 22.31 ∘C?

Answer in g/L to four significant figures.

Question two: A flask has a volume of 148.5 mL . When filled with air at a pressure of 834.6 torr and a temperature of 24.74 ∘C, the flask and air have a mass of 67.887 g . When filled with carbon dioxide at the same temperature and pressure, the mass of the flask and CO₂ is 67.992 g .

Part A - What is the mass of the carbon dioxide gas in the flask (when the flask is filled with carbon dioxide)?

Answer 1

I have a doubt with problem 2, but I can help in problem 1.

With that percent, let's calculate the average MW of dry air:

0.20(32) + 0.80(28) = 28.8 g/mol

If PV = nRT

n = m/MW so replacing above:

PV = mRT/MW

P = mRT/MW V d = m/V so:

P = dRT/MW

d = P*MW/RT

d = 0.90030 * 28.80 / 0.0821 * 295.31

d = 1.069 g/L

Now for the second question, I have my doubt but let me tell you what I can think of. all that we know is the mass of flask + CO2 and flask + air. We also have the volume, Pressure and temperature.

As they are asking mass of CO2 in the flask, we can calculate the number of moles of CO2:

n = PV/RT

P = 834.6 torr / 760 torr = 1.098 atm T = 24.74 + 273 = 297.74 K

n = 1.098 * 0.1485 / 0.0821 * 297.74

n = 6.67x10^-3 moles.

This would be the moles that are inside the flask (in theory). We assume that the volume of the flask is the same as CO2 cause the volume of any gase is equal to the volume of the recipient or flask within.

With the molecular weight of CO2 = 32+12 = 44 g/mol

m CO2 = 44 * 6.67x10^-3 = 0.2934 g

This is, in theory, the mass of the CO2. My doubt is that I don't know what to do with the mass of the flask. Maybe we'll use it on another part.

Tell me in a comment if there's something else, or something that need to be fixed.

Hope this helps