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Percent Composition

Honors Chemistry

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The relative amounts of each element in a compound are expressed as the percent composition, which is the percent by mass of each element in the compound.

It is sometimes useful to know the relative amounts of each of the components compound.

In other words, what is the percentage of nitrogen that you get from the compound sodium nitrate (NaNO3) ?

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The amount of fertilizer that you put on the grass in your yard or on plants in your garden is important.

The relative amount , or the percentage, or each nutrient in the fertilizer is also important.

In spring you may use a fertilizer that has a relatively high percentage of nitrogen, which “greens” you plants.

In the fall you may use a fertilizer that has a higher percentage of potassium to strengthen the root system of your plants.

Real Life Example

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Calculating Percent Composition of a Compound

The following general formula is used to The following general formula is used to determine the percent composition of determine the percent composition of each element in a compound:each element in a compound:

Mass of element (in 1 mole of compound) X 100 Molar Mass of Compound

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What is the percent composition What is the percent composition of each element in Ca(NOof each element in Ca(NO33))22 ? ?

Step 1: Find the molar mass of Ca(NOStep 1: Find the molar mass of Ca(NO33))22 Ca 40.1 grams/moleCa 40.1 grams/mole = 40.1 g/mol = 40.1 g/mol N 2 x (14.0) grams/mole = 28.0g/molN 2 x (14.0) grams/mole = 28.0g/mol O 6 x (16.0) grams/mole = O 6 x (16.0) grams/mole = 96.0 g/mol96.0 g/mol 164.1 g/mole164.1 g/mole

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Step 2: Divide the mass of each element by the Step 2: Divide the mass of each element by the molar mass and multiply by 100 to get the percent.molar mass and multiply by 100 to get the percent.

% Ca = % Ca = 40.140.1g x 100% = 24.4 % Calciumg x 100% = 24.4 % Calcium 164.1g164.1g    % N = % N = 28.028.0g x 100% = 17.1% Nitrogeng x 100% = 17.1% Nitrogen 164.1 g164.1 g    % O = % O = 96.0g96.0g x 100% = 58.5 % Oxygen x 100% = 58.5 % Oxygen 164.1g164.1g

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*Note percent composition can also be done given masses *Note percent composition can also be done given masses

of a compound and each element in the compoundof a compound and each element in the compound..

Calculate the percent composition of a compound that is made of 29.0 grams of Ag with 4.30 grams of S.

29.0 g Ag

33.3 g totalX 100 = 87.1 % Ag

4.30 g S

33.3 g totalX 100 = 12.9 % S

Total = 100 %

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To determine mass of an element that could be recovered from a compound

How many grams of silver can be recovered from a 500gram sample of AgNO3?

% Ag = 107.9 g Ag x 100

169.87g AgNO3

= 63.52% Ag

What is 63.52% of 500grams?

(0.6352) (500) = 317.6 grams Ag

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Using the Mole Concept You can also calculate the last

example as follows.

500 g AgNO3 1 mole AgNO3

169.87 g AgNO3

1 mole Ag

1 mol AgNO3

107.9 g Ag

1 mol Ag

= 317.6 grams Ag

500 g AgNO3