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Calculating Empirical Formula of Urea When The Masses of Its Components Are Known

February 17th, 2008

Chemistry Tutor Site Exercise
Urea one of useful fertilizer contains 1.121 g N, 0.161 g H, 0.480 g C, and 0.640 g O. What is the empirical formula of urea?

Chemistry Tutor Site Solution
Because the mass of each element in urea has been known, so we can calculate the moles of the atoms:

Mole N = 1.121 / 14.01 = 0.08 mol

Mole H = 0.161 / 1.008 = 0.1597 mol

Mole C = 0.480 / 12.01 = 0.039 mol

Mole O = 0.640 / 16.00 = 0.04 mol

Next step is dividing each mole value by 0.039 ( the smallest number of moles present) we obtain:

N : H : C : O = (0.08/0.039) : (0.1597/0.059) : (0.039/0.039) : (0.04/0.039)

N : H : C : O = 2 : 4 : 1 : 1

So the empirical formula of urea is N2H4CO or we can write as (NH2)2CO

Entry Filed under: Determining Formula