A mixture of CH4 and C2H2 occupied a certain volume at a total pressure equal to 63 torr. The same gas mixture was burnt to CO2(g) and H2O(1). The CO2(g) alone wascollected in the same volume and at the same temperature, the pressure was found to be 69 torr.What was the mole fraction of CH4 in the original gas mixture?

Let no. of moles of CH4 present: n, mol. Let no. of moles of C2H2 present = n2 mol.∴ n1+n2=63 torr                       (1)CH4+2O2→CO2(g)+2H2O(l)n1mol→n1molC2H2+3O2→2CO2(g)+H2O(l)n2mol→2n2mol.'. After combustion total no. of moles=n1+2n2=69 torr            (2)∴ n2=6 torr and n1=57 torr ∴ Mole fraction of CH4 in the original gas mix =57 torr 63 torr =1921