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?

Question

30607 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-09-25T14:22:26

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 $C_3H_8$