Question

The simplest formula for butane is C2H5 and its molecular mass is about 60. What is the molecular formula of butane?

Answer 1

The molecular formula for butane is `"C"_4"H"_10"`.

Explanation:

To determine the molecular formula from the empirical (simplest) formula, you need to compare the empirical formula mass to the molecular formula mass.

Divide the molecular formula mass by the empirical formula mass. The result is the factor by which the subscripts in the empirical formula will be multiplied to determine the subscripts of the molecular formula.

To determine the empirical formula mass, multiply the subscript of each element by its atomic weight on the periodic table.

The empirical formula mass is:

`(2xx"12.011 u C") + (5xx"1.008 u H")="29.062 u C"_2"H"_5"`

`"60 u"/"29.062 u"=2` rounded to one significant figure.

Multiply the subscripts of the empirical formula by `2`.

`C_((2xx2))H_((2xx5))="C"_4"H"_10"`

The molecular formula for butane is:

`"C"_4"H"_10`