Question

What is the molecular formula of a compound that has a molecular mass of 54 and the empirical formula C2H3?

Answer 1

The molecular formula is `"C"_4"H"_6"`.

Refer to the explanation for the process.

Explanation:

You have been given the empirical formula for a hydrocarbon. You need to determine the empirical formula mass. Then divide the molecular mass by the empirical mass. Then multiply the subscripts of the empirical formula by the result.

`color(blue)("Empirical Mass of C"_2"H"_3"`
Multiply the subscript of each element by its atomic mass and add.

`"C"_2"H"_3:` `(2xx12.011"u C") + (3xx1.008 "u H")="27.046 u C"_2"H"_3"`

`color(blue)("Determine Molecular Formula"`
Divide the molecular mass by the empirical mass.

`54/(27.046)=2.0` rounded to two sig figs.

Multiply the subscripts in the empirical formula by 2 to get the molecular formula.

`""C_(2xx2)""H_(3xx2)"=C"_4"H"_6"`

The molecular formula is `"C"_4"H"_6"`.