Question

40 ml of hydrocarbon on combustion gave 120 ml $C{O}_2$ and 80 mI water vapour. The molecular formula of hydrocarbon is:

• A. $C_2{H}_6$
• B. $C_3{H}_6$
• C. $C_3{H}_8$
• D. $C_3{H}_4$

Answer 1

Answer: (D)

$C_3{H}_4$

all the Carbon from the hydrocarbon is in the $C{O}_2$

40 ml of hydrocarbon produces 120 ml $C{O}_2$,

1 : 3 ratio

So 1 mole hydrocarbon has 3moles Carbon

All the H ends up in the water

40 ml hydrocarbon produces 80 ml water,

1 : 2 ratio,

but also each water has 2 H atoms

So 1 mole hydrocarbon has 4 moles Hydrogen

which gives

$C_3{H}_4$

answer is D