Percent Composition of Mixtures and Compounds. What is a Percent? A part of a whole A fraction x 100 How many parts out of 100.

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Presentation transcript:

Percent Composition of Mixtures and Compounds

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

The “Percent Formula”

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!

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 g 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%

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)

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!

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