Calculating Oxygen Mass in a 4.0x7.0x2.5 Room

[Zhalfirin88]

Homework Statement

What is the total mass (in grams) of oxygen in a room measuring 4.0 by 7.0 by 2.5? Assume that the gas is at STP and that air contains 20.95% oxygen by volume.

The Attempt at a Solution

I don't know where to begin.

 

[mgb_phys]

Do you know the ideal gas law PV = nRT ?

http://en.wikipedia.org/wiki/Ideal_gas_law

 

[Zhalfirin88]

Yes.

 

[mg0stisha]

Then you have everything you need except the variable n, or the number of moles. There's also an equation that relates n (number of moles) to the mass. Do you know of this equation?

 

[mgb_phys]

Then that gives you the number of moles of air -
Find the average molecular mass of air by assuming that the rest is N2 (mass=28)

Then you know the number of moles of O2 - and so the mass

 

[Zhalfirin88]

V = (4*7*2.5) = 70m^3
P = 1atm
T = 273 K
R = .000082
n = PV/RT
n = 3126.95
1 mole of oxygen is 32 g/mol so
32 * 3126.95 = 1000062.53 but you only want 20.95% of that so
1000062.53 * .2095 = 20963.10
= 2.10 x 10^ 4

 

[Borek]

2.10 x 10^ 4

Pounds? Talents? Stones? Carats? Maunds? Catties? Wiarduneks?