1. Percent Composition, Empirical and Molecular Formulas Courtesy www.lab-initio.com

2. Calculating Percentage Composition Calculate the percentage composition of magnesium carbonate, MgCO 3. Formula mass of magnesium carbonate: 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g 100.00

3. Calculate the percent composition of : Sodium phosphate Potassium sulfate

4. Formulas  molecular formula = (empirical formula) n  molecular formula = C 6 H 6 = (CH) 6  empirical formula = CH Empirical formula: the lowest whole number ratio of atoms in a compound. Molecular formula: the true number of atoms of each element in the formula of a compound.

5. Formulas (continued) Formulas for ionic compounds are ALWAYS empirical (lowest whole number ratio). Examples: NaCl MgCl 2 Al 2 (SO 4 ) 3 K 2 CO 3

6. Formulas (continued) Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio). Molecular: H2OH2O C 6 H 12 O 6 C 12 H 22 O 11 Empirical: H2OH2O CH 2 OC 12 H 22 O 11

7. Empirical Formula Determination 1.Base calculation on 100 grams of compound. Determine moles of each element in 100 grams of compound. 2.Divide each value of moles by the smallest of the values. 3.Multiply each number by an integer to obtain all whole numbers.

8. Empirical Formula Determination Adipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula of adipic acid? 1.Treat % as mass, and convert grams to moles

9. Empirical Formula Determination 2. Divide each value of moles by the smallest of the values. Carbon: Hydrogen: Oxygen:

10. Empirical Formula Determination 3. Multiply each number by an integer to obtain all whole numbers. Carbon: 1.50 Hydrogen: 2.50 Oxygen: 1.00 x 2 352 Empirical formula: C3H5O2C3H5O2

11. A compound is 85.75 % C and 14.3% H. Calculate the empirical formula. What is the name of this compound?

12. A compound contains 63 g of manganese and 37 g of oxygen. What is the empirical formula? What is the name of this compound?

13. Finding the Molecular Formula The empirical formula for adipic acid is C 3 H 5 O 2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid? 1. Find the formula mass of C 3 H 5 O 2 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g

14. Finding the Molecular Formula The empirical formula for adipic acid is C 3 H 5 O 2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid? 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g 2. Divide the molecular mass by the mass given by the emipirical formula.

15. Finding the Molecular Formula The empirical formula for adipic acid is C 3 H 5 O 2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid? 3. Multiply the empirical formula by this number to get the molecular formula. (C 3 H 5 O 2 ) x 2 = C 6 H 10 O 4

16. The percentage composition of a compound is 92.3% C and 7.7% H. If the molecular mass is 78 g/mol, what is the molecular formula?

17. Find the molecular formula of a compound with percentage composition 26.7% P, 12.1% N, and 61.2% Cl and a molecular mass of 695 g/mol.