Question

28cm3 of a gas weighs 0.4g at STP.Calculate the molecular mass of the gas.

Answer 1

well, 1 mole fills 22.4L
28cm^3 = 0.028L

So, you have .028/22.4 = 0.00125 moles (1/800 moles)

Thus, if the mol wt is x grams,

x/800 = 0.4
x = 320