1. Percent Composition of Mixtures and Compounds

2. What is a Percent? A part of a whole A fraction x 100 How many parts out of 100

3. The “Percent Formula”

4. Percent Composition of Mixtures (by mass)  The “whole” will be the mass of the whole entire mixture.  The “part” will be the mass of the part of the mixture you are interested in.  The “percent” will express the part out of 100 equal parts. All percents must add to 100!

5. Example: Percent Composition of a Mixture (by mass) Julia makes a Chex Mix with 150. grams of pretzels, 220. grams of peanuts, and 125 grams of cereal. What is the percent composition of her Chex Mix? Whole = ? 150. g + 220. g + 125 g = 495 g % Pretzels = (150. g / 495 g) * 100 = 30.3% % Peanuts = (220. g / 495 g) * 100 = 44.4% % Cereal = (125. g / 495 g) * 100 = 25.3%

6. Percent Composition of a Compound (by mass) A compound is a “chemical” mixture since a chemical reaction between elements forms a compound (although the elements cannot be separated physically anymore). Ex: 2Na (s) + Cl 2 (g) → 2NaCl (s)

7. Percent Composition of Compounds (by mass)  The “whole” will be the mass of the whole compound (which you can get from the Law of Conservation of Mass)  The “part” will be the mass of the part of the compound you are interested in (which element)  The “percent” will express the part out of 100 equal parts. All percents must add to 100!

8. Example: Percent Composition of a Compound (by mass) 63.98 grams of sodium (Na) metal reacts completely with 70.90 grams of chlorine gas (Cl 2 ) to produce pure sodium chloride (table salt). What is the percent composition of table salt (by mass)? Whole = ? 63.98 g + 70.90 g = 134.88 g (by the Law of Conservation of Mass) % Sodium = (63.98 g/ 134.88 g) * 100 = 47.43 % % Chlorine = (70.90 g / 134.88 g) * 100 = 52.57% Ex: 2Na (s) + Cl 2 (g) → 2NaCl (s)