Question

A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide , 0.690 g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate molar mass of the gas.

Answer 1

        CxHy + O2 ==> CO2 + H2O

         Since the mole ratio of C: H is 1:1,

         So, the empirical formula is CH.

Also, n = molar mass/empirical formula mass

Empirical formula mass= 12 + 1 = 13

26.0 g/13 g = 2

Molecular formula = n X empirical formula =2 X CH =C 2H2 (acetylene)