1. Chapter 7 Preview Lesson Starter Objectives Formula Masses Molar Masses Molar Mass as a Conversion Factor Percentage Composition Section 3 Using Chemical Formulas

2. Chapter 7 Section 3 Using Chemical Formulas Lesson Starter The chemical formula for water is H 2 O. How many atoms of hydrogen and oxygen are there in one water molecule? How might you calculate the mass of a water molecule, given the atomic masses of hydrogen and oxygen? In this section, you will learn how to carry out these and other calculations for any compound.

3. Chapter 7 Section 3 Using Chemical Formulas Objectives Calculate the formula mass or molar mass of any given compound. Use molar mass to convert between mass in grams and amount in moles of a chemical compound. Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound. Calculate the percentage composition of a given chemical compound.

4. Chapter 7 A chemical formula indicates: the elements present in a compound the relative number of atoms or ions of each element present in a compound Chemical formulas also allow chemists to calculate a number of other characteristic values for a compound: formula mass molar mass percentage composition Section 3 Using Chemical Formulas

5. Chapter 7 Formula Masses The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all atoms represented in its formula. example:formula mass of water, H 2 O average atomic mass of H: 1.01 amu average atomic mass of O: 16.00 amu Section 3 Using Chemical Formulas average mass of H 2 O molecule: 18.02 amu

6. Chapter 7 Formula Masses The mass of a water molecule can be referred to as a molecular mass. The mass of one formula unit of an ionic compound, such as NaCl, is not a molecular mass. The mass of any unit represented by a chemical formula (H 2 O, NaCl) can be referred to as the formula mass. Section 3 Using Chemical Formulas

7. Chapter 7 Formula Masses, continued Sample Problem F Find the formula mass of potassium chlorate, KClO 3. Section 3 Using Chemical Formulas

8. Chapter 7 Formula Masses, continued Sample Problem F Solution The mass of a formula unit of KClO 3 is found by adding the masses of one K atom, one Cl atom, and three O atoms. Atomic masses can be found in the periodic table in the back of your book. In your calculations, round each atomic mass to two decimal places. Section 3 Using Chemical Formulas

9. Chapter 7 Formula Masses, continued Sample Problem F Solution, continued Chapter 7 Section 3 Using Chemical Formulas formula mass of KClO 3 = 122.55 amu

10. Chapter 7 Molar Masses The molar mass of a substance is equal to the mass in grams of one mole, or approximately 6.022 × 10 23 particles, of the substance. example: the molar mass of pure calcium, Ca, is 40.08 g/mol because one mole of calcium atoms has a mass of 40.08 g. The molar mass of a compound is calculated by adding the masses of the elements present in a mole of the molecules or formula units that make up the compound. Section 3 Using Chemical Formulas

11. Chapter 7 Molar Masses, continued One mole of water molecules contains exactly two moles of H atoms and one mole of O atoms. The molar mass of water is calculated as follows. Section 3 Using Chemical Formulas molar mass of H 2 O molecule: 18.02 g/mol A compound’s molar mass is numerically equal to its formula mass.

12. Chapter 7 Calculating Molar Masses for Ionic Compounds Chapter 7 Section 3 Using Chemical Formulas

13. Chapter 7 Molar Masses, continued Sample Problem G What is the molar mass of barium nitrate, Ba(NO 3 ) 2 ? Section 3 Using Chemical Formulas

14. Chapter 7 Molar Masses, continued Sample Problem G Solution One mole of barium nitrate, contains one mole of Ba, two moles of N (1 × 2), and six moles of O (3 × 2). Chapter 7 Section 3 Using Chemical Formulas molar mass of Ba(NO 3 ) 2 = 261.35 g/mol

15. Chapter 7 Molar Mass as a Conversion Factor The molar mass of a compound can be used as a conversion factor to relate an amount in moles to a mass in grams for a given substance. To convert moles to grams, multiply the amount in moles by the molar mass: Amount in moles × molar mass (g/mol) = mass in grams Section 3 Using Chemical Formulas

16. Chapter 7 Mole-Mass Calculations Chapter 7 Section 3 Using Chemical Formulas

17. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem H What is the mass in grams of 2.50 mol of oxygen gas? Section 3 Using Chemical Formulas

18. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem H Solution Given: 2.50 mol O 2 Unknown: mass of O 2 in grams Solution: moles O 2 grams O 2 amount of O 2 (mol) × molar mass of O 2 (g/mol) = mass of O 2 (g) Section 3 Using Chemical Formulas

19. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem H Solution, continued Calculate the molar mass of O 2. Section 3 Using Chemical Formulas Use the molar mass of O 2 to convert moles to mass.

20. Chapter 7 Converting Between Amount in Moles and Number of Particles Chapter 7 Section 3 Using Chemical Formulas

21. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem I Ibuprofen, C 13 H 18 O 2, is the active ingredient in many nonprescription pain relievers. Its molar mass is 206.31 g/mol. a.If the tablets in a bottle contain a total of 33 g of ibuprofen, how many moles of ibuprofen are in the bottle? b.How many molecules of ibuprofen are in the bottle? c.What is the total mass in grams of carbon in 33 g of ibuprofen? Section 3 Using Chemical Formulas

22. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem I Solution Given:33 g of C 13 H 18 O 2 molar mass 206.31 g/mol Unknown:a. moles C 13 H 18 O 2 b. molecules C 13 H 18 O 2 c. total mass of C Solution:a. grams moles Section 3 Using Chemical Formulas

23. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem I Solution, continued b. molesmolecules Section 3 Using Chemical Formulas c. moles C 13 H 18 O 2 moles C grams C

24. Chapter 7 Molar Mass as a Conversion Factor, continued Sample Problem I Solution, continued Section 3 Using Chemical Formulas a. b. c.

25. Chapter 7 Percentage Composition It is often useful to know the percentage by mass of a particular element in a chemical compound. To find the mass percentage of an element in a compound, the following equation can be used. Section 3 Using Chemical Formulas The mass percentage of an element in a compound is the same regardless of the sample’s size.

26. Chapter 7 Percentage Composition, continued The percentage of an element in a compound can be calculated by determining how many grams of the element are present in one mole of the compound. Section 3 Using Chemical Formulas The percentage by mass of each element in a compound is known as the percentage composition of the compound.

27. Chapter 7 Percentage Composition of Iron Oxides Chapter 7 Section 3 Using Chemical Formulas

28. Chapter 7 Percentage Composition Calculations Chapter 7 Section 3 Using Chemical Formulas

29. Chapter 7 Percentage Composition, continued Sample Problem J Find the percentage composition of copper(I) sulfide, Cu 2 S. Section 3 Using Chemical Formulas

30. Chapter 7 Percentage Composition, continued Sample Problem J Solution Given: formula, Cu 2 S Unknown: percentage composition of Cu 2 S Solution: formula molar mass mass percentage of each element Section 3 Using Chemical Formulas

31. Chapter 7 Percentage Composition, continued Sample Problem J Solution, continued Section 3 Using Chemical Formulas Molar mass of Cu 2 S = 159.2 g

32. Chapter 7 Percentage Composition, continued Sample Problem J Solution, continued Section 3 Using Chemical Formulas