Determine the empirical formula of an unknown Compound having a percent composition of 3.74% H, 17.83% C, and 38.43 % Pb.(Molar mass: Pb =207.20 g/mol; C=12.01 g/mol; H = 1.01 g/mol).
To determine the empirical formula, we need to find the smallest whole number ratio of atoms in the compound.
1. Calculate the number of moles of each element:
H: 3.74 g / 1.01 g/mol = 3.71 mol
C: 17.83 g / 12.01 g/mol = 1.48 mol
Pb: 38.43 g / 207.2 g/mol = 0.185 mol
2. Find the smallest mole ratio by dividing each value by the smallest number of moles:
H: 3.71 mol / 0.185 mol = 20.05 ≈ 20
C: 1.48 mol / 0.185 mol = 8
Pb: 0.185 mol / 0.185 mol = 1
3. Write the empirical formula using the whole number ratios:
Empirical formula = PbC8H20
To determine the empirical formula of the unknown compound, we need to find the simplest whole-number ratio of the elements present in the compound.
Step 1: Convert the percent composition to grams.
- Assume we have a 100 g sample of the compound.
- 3.74% H is equal to 3.74 grams of H.
- 17.83% C is equal to 17.83 grams of C.
- 38.43% Pb is equal to 38.43 grams of Pb.
Step 2: Determine the moles of each element.
- Divide the mass of each element by its molar mass (given in the problem).
- Moles of H = 3.74 g / 1.01 g/mol = 3.70 mol H
- Moles of C = 17.83 g / 12.01 g/mol = 1.48 mol C
- Moles of Pb = 38.43 g / 207.20 g/mol = 0.185 mol Pb
Step 3: Find the simplest whole-number ratio.
- Divide each mole value by the smallest mole value to get the simplest ratio.
- Moles of H / Moles of Pb = 3.70 mol H / 0.185 mol Pb = 20
- Moles of C / Moles of Pb = 1.48 mol C / 0.185 mol Pb = 8
The simplest whole-number ratio of elements is H20C8. So, the empirical formula of the unknown compound is H20C8.