Question

A gaseous compound consists of 86% carbon and 14% hydrogen by mass. At s.t.p, 3.2dm³ of the compound has a mass of 6g. (C = 12 H = 1 molar gas volume at s.t.p = 22.4dm³)

1. Calculate its empirical formula  
2. Calculate its molecular formula   

Answer 1

1.  

   Elements	C	H
   % Mass	86	14
   RAM	12	1
   Moles	86/12 =7.166	14/1=14
   Mole ratio	7.166  7.166   1   1	14    7.166  1.95   2

   E.F =CH₂

2. If 3.2dm³   → 6g
    22.4dm³ → ?
   22.4 × 6   =42 
       3.2
   MF=(EF)_n
   n=R.M.M
        E.F.M
    =⁴²/₁₄=3 
   MF =(CH₂)₃
    =C₃H₆