Question

The empirical formula of a compound is $ C{{H}_{2}} $ 1 mole of this compound has a mass of $ 42g $ . Its molecular formula is:

• A. $ {{C}_{2}}{{H}_{2}} $
• B. $ C{{H}_{2}} $
• C. $ {{C}_{3}}{{H}_{8}} $
• D. $ {{C}_{3}}{{H}_{6}} $

Answer 1

Answer: (D)

Empirical formula weight of $ C{{H}_{2}}=12+(1\times 2) $
$ =12+2 $ $ =14 $
Mass of 1 mole of the compound = its molecular weight
$ =42 $ $ n=\frac{molecular\,weight}{empirical\,formula\,weight} $
$ =\frac{42}{14}=3 $
$ \therefore $ molecular formula = (empirical formula) $ \times n $
$ =(C{{H}_{2}})\times 3 $ $ ={{C}_{3}}{{H}_{6}} $