1st step - Determine the minimum formula using the percentage formula. We consider that the percentage of each compound is for 100g of the compound. Then, we divide the mass quantity by the atomic mass of the element:
Carbon:
64.67/12 = 5.389
Hydrogen:
5.92/1 = 5.92
Nitrogen:
13.71/14 = 0.9793
Now we divide each number by the smallest number (0.9793):
C - 5.389/0.9793 = 5.5
H - 5.92/0.9793 = 6
N - 0.9793/0.9793 = 1
The value of C is decimal. So we need to transform it into an integrer. Let's multiple by 2:
C - 11
H - 12
N - 2
a) The empirical formula is C11H12N2