please help - grams of air
 

How many grams of air would be in an otherwise empty 2.00-liter beverage container at a pressure of 750 torr and temperature of 27 °C? Since air is about one-fifth oxygen and four-fifths nitrogen, we often treat it as a single gas with an average molar mass of 29 g/mol.

Again we have to use this formula:

p*V = n*R*T

p in Pa... 750 torr = 99991.78 Pa
V in cubic metres = 0.002 m3
R is a constant = 8.3145 whatever
T is in Kelvin = 300.15 K

n = (99991.78*0.002)/(8.3145*300.15) = 0.08 mol

So we have 0.08 mol gas in the bottle, and we know the molar mass.

1 mol of the gas is 29 g.
So 0.08 mol of the gas is 29*0.08 mol = 2.32 g of air. Pretty light huh?