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

2 Answers
Nov 7, 2015

The molecular formula is always a multiple of the empirical formula. MF = nxxEF.

Explanation:

So, (CHOCl)xxn = MF;

i.e. (12.011 + 1.00794 + 15.999 + 35.45)xxn*g*mol^-1 = 129.0*g*mol^-1.

Clearly n=2. The molecular formula, a multiple of the empirical formula, is C_2H_2Cl_2O_2, or rather Cl_2CH-C(=O)OH.

Nov 8, 2015

The molecular formula for dichloroacetic acid is "C"_2"H"_2"O"_2"Cl"_2" or "CHCl"_2"COOH".

Explanation:

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

Determine the empirical formula mass for "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=(129cancel"g/mol")/(64.546cancel"g/mol")=2.00

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

The molecular formula for dichloroacetic acid is "C"_2"H"_2"O"_2"Cl"_2" or "CHCl"_2"COOH".