Elemental analysis of a compound, once used as a pesticide, was found to be 74.2% carbon, 8.64% hydrogen, and 17.2% nitrogen. What is the empirical formula of this compound?
Take a 100 g sample and that contains
74.2 g C
8.64 g H
17.2 g N
Convert to mols
74.2/12 = ?
8.64/1 = ?
17.2/14 = ?
Now find the ratio of these three elements to each other with the lowest number being 1.00. The easy way to do that is to divide the smallest number by itself (making it 1.00 of course), then divide the other values by the same number. Round to whole numbers. Those whole numbers will give you the subscripts for CxHyNz. Post your work if you get stuck.
To determine the empirical formula of a compound, we need to find the simplest whole-number ratio of the elements present in the compound.
Let's assume we have 100 grams of the compound. From the given percentages, this means we have:
- 74.2 grams of carbon (C)
- 8.64 grams of hydrogen (H)
- 17.2 grams of nitrogen (N)
Next, we need to find the moles of each element. To do this, we divide the mass of each element by its molar mass.
The molar mass of carbon (C) is 12.01 g/mol.
The molar mass of hydrogen (H) is 1.008 g/mol.
The molar mass of nitrogen (N) is 14.01 g/mol.
For carbon:
moles of carbon = mass of carbon (g) / molar mass of carbon
moles of carbon = 74.2 g / 12.01 g/mol = 6.18 mol
For hydrogen:
moles of hydrogen = mass of hydrogen (g) / molar mass of hydrogen
moles of hydrogen = 8.64 g / 1.008 g/mol = 8.57 mol
For nitrogen:
moles of nitrogen = mass of nitrogen (g) / molar mass of nitrogen
moles of nitrogen = 17.2 g / 14.01 g/mol = 1.23 mol
Next, we need to find the simplest whole-number ratio of these moles. We divide each mole value by the smallest mole value to get a ratio.
Dividing by 1.23 mol gives us the following ratios:
moles of carbon = 6.18 mol / 1.23 mol = 5.02
moles of hydrogen = 8.57 mol / 1.23 mol = 6.97
moles of nitrogen = 1.23 mol / 1.23 mol = 1
Now, we have the ratio of the elements in the simplest whole-number form: C5H7N. Therefore, the empirical formula of the compound is C5H7N.