First, you need to find the empirical formula of the compound (histamine).
To find the empirical formula convert all the data given in mass units (miligrams) into mole numbers.
You do that by using the formula: number of moles = mass in grams / atomic mass.
To find the mass in grams divide the mass in miligrams by 1,000.
Build a table:
Element mass (g) atomic mass (g/mol) number of moles (mol)
C 0.208 12.011 0.0173
H 0.031 1.008 0.0307
N 0.146 14.007 0.0104
Now, find the ratio C:H:N, for which you divide every number of moles by the smallest number of moles: 0.0104:
- C: 0.0173 / 0.0104 = 1.665
- H: 0.0307 / 0.0104 = 2.957
- N: 0.0104 / 0.104 = 1.002
You must find a multiple that yields 1.665 to a reasonably close integer.
Muliply every amount by 3:
Hence, the empirical formula is C₅H₉N₃.
Now, find the mass of the empirical formula:
- 5(12.011 g/mol) + 9(1.008 g/mol) + 3(14.007 g/mol) = 111.148 g/mol ≈ 111 g/mol.
Since the mass of the empirical formula is the same of the molecular formula, both formulae are the same.
Therefore, the answer is: C₅H₉N₃ ← molecular formula