a sample of natural gas is 85.2% methan, CH4, and 14.8% ethane, C2H6, by mass. What is the density of this mixture @ 18C and 748mmHg.

Question

so i know that i have to use this formula
d=(PM)/(RT) but i don't know how to convert the percentages into g/mol (molecular weight)
can someone help me please?
thanks

Answer 1

0.852 x 16 = ?? for the methane part.
0.148 x 30 = ?? for the ethane part.
mass methane part + mass ethane part = effective molar mass of the mixture.

Answer 2

just for future references can u also put the units so i know what to cancel out and what units i will end up with?
thanks

Answer 3

0.852 x (16.04 g/mol) = 13.666 grams/mol.
0.148 x (30.07 g/mol) = 4.45036 grams/mol
18.11636 g/mol which rounds to 18.1 to three s.f.
Actually you are only using molar masses and multiplying them by a fraction so you still have molar mass when finished.

Answer 4

thanks :D