Aim: How to calculate Percent Composition

[Pages:16]Aim: How to calculate Percent Composition

DO NOW: 1. What is the number of moles of

potassium chloride present in 148 g? 2. What is the molar mass of CuSO4 5H2O? 3. What is the mass of 3.01 x 1023 atoms of

carbon?

Percent Composition

The percent composition is the mass percentage of each type of atom (element) in a compound.

%

mass

of

element

=

x

100%

Percent Composition from Mass

Data

Percent composition can be calculated from experimental data.

A student prepares a compound of tungsten chloride from 3.946 g of tungsten and 3.806 g of chlorine. Calculate the percent composition.

%

W

=

2

x

100%

=

3.946 7.752

x

100%

=

50.9

%

% Cl = x 100% = 3.806 x 100% = 49.1 %

2

7.752

Percent Composition from Chemical Formula

% mass = 1 x 100%

Percent Composition from Chemical Formula

To calculate the percent composition of a component in a compound:

1. Find the molar mass of the compound by adding up the masses of each atom in the compound.

2. Calculate the molar mass of the component in the compound for which you are solving.

3. Divide the molar mass of the component by the total molar mass of the compound and multiply by 100

Percent Composition from Chemical Formula

Step1 8C + 10H +4N + 2O (8 x 12.0 g/mol) + (10 x 1.0 g/mol) + ( 4 x 14.0 g/mol) + (2 x 16.0 g/mol) = 194.0 g/mol

Step 2 Carbon: 8 12.0 / x 100% = 49.5 %

194 /

Hydrogen: 10 1.0 / x 100% =5.1 %

194 /

Nitrogen: 4 14.0 / x 100% = 28.9 %

194 /

Oxygen: 100% - (49.5 + 5.1 + 28.9) = 16.5 %

Percent Composition of Crystal Hydrates

A HYDRATE is a CRYSTALLINE compound in which ions are attached to one or more WATER molecules.

Example: Na2CO3 10H2O Notice how WATER molecules are BUILT INTO the

chemical formula

Substances without water built into the formula are called ANHYDRATES.

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