When 100ml sample of methane and ethane along with excess of oxygen is subjected to electric spark , the contraction in volume was observed to 212ml , when resulting gas is passed through KOH solution , further contraction in volume was ?

Dear Student

According to the question, the reaction taking place is -
CH₄ (g)  +  2O₂ (g) ----> CO₂ (g)   +  2H₂O (l)
  (x)                (2x)            (x)


C₂H₆ (g)      +      7/2O₂ (g)       ---->     ​2O₂ (g)    +   3H₂O (l)
 (100 - x)            ​7/2(100 - x)                2(100 - x)

So, the total contraction in volume would be-
2x + 2.5(100 -x) = 212
2x + 250 - 2.5x = 212
2x - 2.5x = 212 - 250
-0.5 x = - 38
x = 76

So, the contraction in volume when passed through KOH solution would be = Volume of CO₂ evolved
                                                                                                                          = x + 2(100 - x) = 76 + 200 - (2 x 76)
                                                                                                                          = 276 - 152 = 124 ml

Regards