Question

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

Answer 1

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`.

Answer 2

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"`.