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

Answer:

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

Answer:

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"#.