A carbon compound contains 12.8% carbon 2.1% Hydrogen 85.1% bromine. The molecular weight of the compound is 187.9 calculate the molecular formula.

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Detailed Solution

Element	%	Atomic Weight	%/At.wt	Simple ratio
C	12.8	12	$\frac{12.8}{12} = 1.067$	$\frac{1.067}{1.067} = 1$
H	2.1	1	$\frac{2.1}{1} = 2.1$	$\frac{2}{1.067} = 2$
Br	85.1	80	$\frac{85.1}{80} = 1.067$	$\frac{1.067}{1.067} = 1$

Empirical formula = CH₂Br
Empirical formula weight
= 12 + (2 × 1) + 80 = 94
The molecular weight =187.9 (given)
$n = \frac{molecular weight}{empirical formula weight} = \frac{187.9}{94} = 2$
Molecular formula = (Empirical formula)_n
${({CH}_{2} Br)}_{2} = C_{2} H_{4} {Br}_{2}$