The actual amount of substance doesn’t matter for this problem, so assume an easy mass of compound using the percentages: 82.63 g C and 17.37 g H. There is also no need to worry about significant figures in an empirical formula problem.
Find the number of moles of each element:
[tex](82.63 \text{ g C})(\frac{1 \text{ mol C}}{12.011 \text{ g C}} )=6.88 \text{ mol C}\\(17.37 \text{ g H})(\frac{1 \text{ mol H}}{1.0078 \text{ g H}} )=17.2 \text{ mol H}[/tex]
Find the ratio of the elements, and simplify until there are whole numbers that you can put into the empirical formula.
[tex]\frac{17.2 \text{ mol H}}{6.88 \text{ mol C}} =\frac{2.5 \text{ mol H}}{1 \text{ mol C}}=\frac{5 \text{ mol H}}{2 \text{ mol C}}[/tex]
There are 5 mol H for every 2 mol C, so the empirical formula should be [tex]{\text{C}}_2{\text{H}}_5[/tex].
