`10 mL` of a gaseous hydrocarbon is exploded with `100 mL` of oxygen. The residual gas on cooling is found to measure `95 mL` of which `20 mL` is absorbed by caustic soda and the remainder by alkaline pyrollgallol. The fomula of the hydrocarbon is

Options

A. `CH_(4)`
B. `C_(2)H_(6)`
C. `C_(2)H_(4)`
D. `C_(2)H_(2)`

Answer

D

Explanation

`underset({:(1 mL),(10mL):})(C_(x)H_(y)) + underset({:((x + (y)/(4)) mL),(10(x + (y)/(4))mL):})((x + (y)/(4)) O_(2)) rarr underset({:(x mL),(10 x mL):})(xCO_(2)) + underset({:((y)/(2) ml):})((y)/(2) H_(2)O`
Volume absorbed by `KOH =` volume of `CO_(2)`
Volume of `CO_(2) = 20 mL`
`:. 10 x = 20`
`x = 2 mL = 2 "mol"`
volume obserbed by alkaline pyrogallol = volume of `O_(2)`
`= 95 - 20`
`= 75 mL`
Excess of `O_(2) = 75 mL`
Total `O_(2) = 100 mL`
volume of `O_(2)` reacted `= 100 - 75 = 25 mL`
`:. 10 (x + (y)/(4)) = 25 ml`
`:. y = 2`
Formula of hydrocarbon `= C_(2) H_(2)`