Question on volatile liquid compund...

Question

A volatile liquid compound was found to be composed of carbon and hydrogen in the ratio of one mole of carbon atoms to two moles of hydrogen. If 0.124g of the vapour at 100 degrees celcius and one atmosphere pressure gives rise to 45cm^3 of volume then:

1. what is the gram molecular mass of the liquid?

2. what is the molecular formular of the liquid?

Answer 1

find moles:

PV=nRt

(1atm)(0.045 litres) = n (0.08206 L-atm / mol-K) (373K)

n= 1.47e-3 moles

1. what is the gram molecular mass of the liquid

0.124 grams / 1.47e-3 = 84.35 grams / mole

your answer ( 3 sig figs): 84.4 g/mol

2. what is the molecular formular of the liquid,

if CH2 has an empirical formula mass of 14 g/mol, the molar mass @ 84 , is 7 times larger, .... so the molecular formula is 7 times larger:

your answer is C7H14