B. Example Calculations
1. An oxide of aluminum is formed by the reaction of 4.151 g of aluminum with 3.692 g of oxygen. Calculate the empirical formula for this compound?
Elements: Al O
Grams: 4.151g 3.692g
Mole: 0.1538 mol 0.2308 mol
Lowest mole: 0.1538 0.1538
mole/lowest mole: 1 3.002
Ratio: 2 3
Answer is Al2O32. The molecular formula is molar mass of Molecular formula divided by molar mass of empirical formula.
A compound with empirical formula CH2 was found by experiment to have a molar mass of approximately 84 g. What is the molecular formula of this compound?
84/14.0268=5.98=6
(CH2)6
The answer is C6H12
3. Identify the different types of Chemical Formulas:
C4H8O4 Answer: empirical
C12H4Cl4O2 Answer: molecular
C3H8N Answer: empirical
4. For Percent Composition, take a compound such as CH and find the percent of C in the compound.
Find the molar mass of the whole compound which is 13.0189. Then take the molar mass of C which is 12.011. Then take 12.011/13.0189 times 100 to find the percent composition of C.
The answer is 92%.
5. What is the molar mass of Fr2S?
Answer: 478g/mol
Elements: Al O
Grams: 4.151g 3.692g
Mole: 0.1538 mol 0.2308 mol
Lowest mole: 0.1538 0.1538
mole/lowest mole: 1 3.002
Ratio: 2 3
Answer is Al2O32. The molecular formula is molar mass of Molecular formula divided by molar mass of empirical formula.
A compound with empirical formula CH2 was found by experiment to have a molar mass of approximately 84 g. What is the molecular formula of this compound?
84/14.0268=5.98=6
(CH2)6
The answer is C6H12
3. Identify the different types of Chemical Formulas:
C4H8O4 Answer: empirical
C12H4Cl4O2 Answer: molecular
C3H8N Answer: empirical
4. For Percent Composition, take a compound such as CH and find the percent of C in the compound.
Find the molar mass of the whole compound which is 13.0189. Then take the molar mass of C which is 12.011. Then take 12.011/13.0189 times 100 to find the percent composition of C.
The answer is 92%.
5. What is the molar mass of Fr2S?
Answer: 478g/mol