Question

A compound containing only carbon, nitrogen, and hydrogen is analyzed to contain 58.82% carbon, 27.45% nitrogen, and 13.73% hydrogen (by mass), What is its simplest formula?

Answer 1

When given percents for an empirical formula problem, first consider all the percents as grams.

58.82% carbon —> 58.82 g carbon
27.45% nitrogen —> 27.45 g nitrogen
13.73% hydrogen —> 13.73 g hydrogen

Then convert the grams of all the elements to moles, based on their molar masses.

Carbon - 58.82 g / 12.01 g/mol = 4.898 mol carbon

Nitrogen - 27.45 g / 14.01 g/mol = 1.959 mol nitrogen

Hydrogen - 13.73 g / 1.008 g/mol = 13.62 mol hydrogen

Then divide all of the mole numbers by the smallest number of moles, which is in this case, the 1.959 mol of nitrogen.

Carbon - 4.898 / 1.959 = 2.5

Nitrogen - 1.959 / 1.959 = 1

Hydrogen - 13.62 / 1.959 = 7

You want whole numbers for all of your mole numbers, so multiply all of them by 2, since 2.5 isn’t a whole number.

Final answer: C5N2H14