# Percent Composition Percent Composition The gram formula mass

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Percent Composition

Percent Composition The gram formula mass of a compound represents the TOTAL MASS of the compound What percent of the total mass is each element in the compound? Remember: percent means “out of 100”

For example…. This cup contains a total mass of 100 g of liquid. 75 g are “coffee” and 25 g are “cream”. What is the percent composition of the liquid in the cup? 75 g coffee 100 g total x 100 = 75% coffee 25 g cream 100 g total x 100 = 25% cream

What is the percent composition of potassium chlorate? Formula = KCl. O 3 Gram Formula Mass : K = 1 x 39 = 39 Cl = 1 x 35. 5 = 35. 5 O = 16 x 3 = 48 +______ 122. 5 g What percent of the total mass (122. 5 g) is each of the elements (K, Cl, and O) in the compound?

K = 39 g 122. 5 g x 100 = 31. 8 % Cl = 35. 5 g 122. 5 g x 100 = 29. 0 % O 3 = 48 g 122. 5 g x 100 = 39. 2 % + ____ 100 %

Percent composition formula is in Table T (back page) mass of part mass of whole x 100

You try it! What is the percent composition of Mg. Br 2? Mg = 24 g x 1 = 24 g Br = 80 g x 2 = 160 g +_____ 184 g Mass of whole % Mg 24 g (mass of part) 184 g x 100 % Br 160 g 184 g = x 100 = 13. 0 % 87. 0 %

% Composition and Hydrates Same as other compounds, except treat the “water” as a part: What is the % composition of water in the hydrated compound Na 2 CO 3 • 10 H 2 O

Na 2 CO 3 • 10 H 2 O Total mass (GFM) = 286 g Mass of water (the “part”) = 10 x 18 g = 180 g % composition of water = 180 g x 100 = 62. 9 % water 286 g

You try it! What is the percent composition of water and calcium sulfate in the hydrated compound Ca. SO 4 • 2 H 2 O 21 % water 79 % calcium sulfate