A gaseous alkane on complete combustion gives `CO_(2)` and `H_(2)O`. If the ratio of moles `O_(2)` needed for compustion and moles of `CO_(2)` formed is `5:3` find out the formula of alkane.

Explanation

Let the alkane be `C_(n)H_(2n+2)`
`C_(n)H_(2n+2)+[n+(n+1)/(2)]O_(2)rarrnCO_(2)+(n+1)H_(2)O`
`("Mole of"O_(2))/("Mole of" CO_(2))=(n+(n+1)/(2))/(n)=(5)/(3) or n=3`
Thus, alkane is `C_(3)H_(8)`.