Posted by Susan on .
If 9.03 x 1021 molecules of a compound having general formula CnH2n+2 weigh 1.71g, what is the molar mass of the compound? Give its molecular formula

Chemistry 
DrBob222,
mols = 9.03E21/6.02E23 = 0.015
mol = grams/molar mass
molar mass = grams/mol = 1.71/0.015 = about 114 for molar mass. .
CnH2n means there will be a CH3 on each end with those in the middle being 14. How many units of 14 do we have? That will be 11430(two ends) = 84 and 84/14 = 6; therefore, the formula must be C8H18