2. Friday, April 15 th : “A” Day Monday, April 18 th : “B” Day Agenda  Homework Problems/Questions  Finish Section 7.3 (we’re almost done…)  In-Class: Section 7.3 review, pg. 248: #1-7 (6,7 abc ONLY) Concept Review: “Formulas and Percentage Composition”: #11-15  Quiz over section 7.3 (last ½ hour) Next time: ACT sample science test Lab Write-Up

3. Chemical Formulas can give Percentage Composition  If you know the chemical formula of any compound, you can calculate the percentage composition. 1.From the subscripts, determine the mass contributed by each element and add these to get molar mass. 2.Divide the mass of each element by the molar mass. 3.Multiply by 100 to find the percentage composition of that element.

4. CO and CO 2 are both made up of C and O, but they have different percentage compositions.

5. Using a Chemical Formula to Determine Percentage Composition (Sample Problem I, pg. 247) Calculate the percentage composition of copper (I) sulfide.  The formula for copper (I) sulfide is: Cu 2 S because copper is 1+ and the sulfide ion is 2-

6. Sample Problem I, continued… 1.Find the molar mass of Cu 2 S: Cu = 2 (63.55 g/mol) = 127.1 g/mol S = 32.07 g/mol Molar mass of Cu 2 S: 159.17 g/mol

7. Sample Problem I, continued… 2. Divide the mass of each element in the compound by the molar mass of the compound. 3. Then multiply by 100% to get the % composition. For Cu = 2 (63.55) X 100% = 79.85 % 159.17 For S = 32.07 X 100% = 20.15% 159.17  Check your work, when added together, the sum should be near 100%

8. Additional Practice Determine the percentage composition of H 2 SO 3. 1.Find molar mass of H 2 SO 3. H: 2 (1.01 g/mol) = 2.02 g/mol S: 32.07 g/mol O: 3 (16.00 g/mol) = 48.00 g/mol Molar mass of H 2 SO 3 = 82.09 g/mol

9. Additional Practice 2. Divide the mass of each element in the compound by the molar mass of the compound. 3.Then multiply by 100% to get the % composition For H = 2 (1.01) X 100% = 2.46% 82.09 For S = 32.07 X 100% = 39.07% 82.09 For O = 3 (16.00) X 100% = 58.47% 82.09

10. In-Class Assignments  Section 7.3 review, pg. 248: #1-7 (6,7 a,b,c ONLY)  Concept Review: “Formulas and Percentage Composition”: #11-15

11. Section 7.3 Quiz “Formulas and Percentage Composition”  Use your guided notes and your book to complete this quiz on your own…