1. Percent Composition Thornburg 2014

2. Example 1. Barney has a box of 12 assorted doughnuts. 3 of these doughnuts are chocolate. What percentage of Barney's doughnuts are chocolate? (note, we are talking about total number, not mass, in this case.) number of chocolate doughnuts % of doughnuts that are chocolate = ----------------------------------------------------- x 100 Total number of doughnuts 3 % of doughnuts that are chocolate = ----------- x 100 12 % of doughnuts that are chocolate = 25% Thornburg 2014

3. Example 2. Fred goes to a school that has 258 total students. If 94 of the students are girls, what percentage of the student body is made up of girls? number of girls % of the student body that is made up by girls = -------------------------- x 100 Total number of students 94 % of the student body that is made up by girls = -------------------------- x 100 258 % of the student body that is made up by girls = 36.4% Thornburg 2014

4. In both cases, you found the percent composition by dividing one part by the total and multiplying by 100. percent part composition = --------------------- x 100% whole Thornburg 2014

5. Practice 1.Calculate the percent composition, by mass, of a 600 g solution that contains 2.5 moles of glucose (C 6 H 12 O 6 ). a. What percentage of the solution is water? b. What percentage of the solution is glucose? Thornburg 2014

6. 2. A solution of salt (NaCl) water contains 100 moles of water and 20 moles of NaCl. a. Based on the number of moles, what percent of the solution is NaCl? b. Based on mass, what percent of the solution is NaCl? Thornburg 2014

7. 3.Clyde has mixed a solution of vitamin C and sucrose with water. Clyde’s solution has a mass of 750 g. The solution must be 18% sucrose and 15% vitamin C, by mass. a. How many moles of water should Clyde mix into his solution? b. Based on number of moles, what percentage of the solution is vitamin C? Thornburg 2014