What is the molecular formula of dichloroacetic acid if the emperical formula is CHOCl and the gram molecular mass is 129.0 g?

Nov 7, 2015

The molecular formula is always a multiple of the empirical formula. $M F$ $=$ $n \times E F$.

Explanation:

So, $\left(C H O C l\right) \times n$ $=$ $M F$;

i.e. $\left(12.011 + 1.00794 + 15.999 + 35.45\right) \times n \cdot g \cdot m o {l}^{-} 1 = 129.0 \cdot g \cdot m o {l}^{-} 1$.

Clearly $n = 2$. The molecular formula, a multiple of the empirical formula, is ${C}_{2} {H}_{2} C {l}_{2} {O}_{2}$, or rather $C {l}_{2} C H - C \left(= O\right) O H$.

Nov 8, 2015

The molecular formula for dichloroacetic acid is $\text{C"_2"H"_2"O"_2"Cl"_2}$ or $\text{CHCl"_2"COOH}$.

Explanation:

The gram molecular mass is a multiple of the empirical formula mass.

Determine the empirical formula mass for $\text{CHOCl}$ by multiplying the subscript of each element times its molar mass (atomic weight on the periodic table in g/mol).

(1xx12.0107 "g/mol")+(1xx1.00794"g/mol")+(1xx15.999"g/mol")+(1xx35.453"g/mol")="64.564 g"

To determine the multiplication factor, $n$, divide the gram molecular mass by the empirical formula mass.

$n = \left(129 \cancel{\text{g/mol")/(64.546cancel"g/mol}}\right) = 2.00$

To determine the molecular formula for dichloroacetic acid, multiply the empirical formula times $2$.

The molecular formula for dichloroacetic acid is $\text{C"_2"H"_2"O"_2"Cl"_2}$ or $\text{CHCl"_2"COOH}$.