Hydrocarbon contains 18.18% hydrogen and 81.82% carbon. One litre of this gas has the same mass as carbon dioxide. What is the molecular formula of this hydrocarbon?

1 Answer
Sep 25, 2016

Given the percentage composition of HC as #C->81.82% and H->18.18%#

So the ratio of number if atoms of C and H in its molecule can will be

#C:H=81.82/12:18.18/1#

#C:H=6.82:18.18#
#=6.82/6.82:18.18/6.82=1:2.66~~3:8#

So the Empirical Formula of hydrocarbon is #C_3H_8#

As the mass of one litre of hydrocarbon is same as that of #CO_2# The molar mass of the HC will be same as that of #CO_2# i.e #44g/"mol"#

Now let Molecular firmula of the HC be #(C_3H_8)_n#

Using molar mass of C and H the molar mass of the HC from its molecular formula is
#(3xx12+8xx1)n=44n#

So

#44n=44=>n=1#

Hence the molecular formula of HC is #C_3H_8#