1. Aim: How do I calculate Percent Composition?
DO NOW:
Write down the steps needed to calculate % composition in pairs of two.
What % of total mass of H2O is due to the mass of hydrogen?
Take out your HW and place it on the right corner of your desk.
More Practice: Review Book: More Practice( Pgs. 46- top of 51)
HW: Bring Review Book in tomorrow + Finish worksheet

2. Percent Composition
The percent composition is the mass percentage of each type of atom (element) in a compound.
% mass of element = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 x 100%
How to Calculate % Composition

3. How Can We Use % composition in our daily life?
How to Calculate % Composition

4. Percent Composition from Chemical Formula : Table T
Take Out Table T on your reference table.
% mass = mass of part/mass of whole X 100

5. Percent Composition from Chemical Formula
To calculate the percent composition of a component in a compound:
Find the molar mass of the compound by adding up the masses of each atom in the compound.
Calculate the molar mass of the component in the compound for which you are solving.
Divide the molar mass of the component by the total molar mass of the compound and multiply by 100
How to Calculate % Composition

6. Percent Composition of Nitrogen in C8H10N4O2?
Step1 find molar mass
C8H10N4O2
8C + 10H +4N + 2O
(8 x 12.0 g/mol) + (10 x 1.0 g/mol) + ( 4 x g/mol) + (2 x 16.0 g/mol) = g/mol
How to Calculate % Composition

7. Calculate the molar mass of the component you are solving for in the problem.
C8H10N4O2?
Step 2
Nitrogen: x 100% = 28.9 %
STEP 3: DIVISION AND MULTIPLY BY 100- 28.9 %

8. Percent Composition from Mass Data
Percent composition can be calculated from experimental data.
A student prepares a compound of tungsten chloride from g of tungsten and g of chlorine. Calculate the percent composition.
% W = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑊 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑊 𝐶𝑙 2 x 100% = 𝑔 x 100% = 50.9 %
% Cl = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐶𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑊 𝐶𝑙 2 x 100% = 𝑔 x 100% = 49.1 %

9. 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.
How to Calculate % Composition

10. Problem: What is the percentage by mass of water in sodium carbonate crystals (Na2CO3 10H2O)?
Step 1: Calculate the formula mass for the hydrate.
Na = 2 x 23.0 g/ mol = g/mol
C = 1 x g/mol = 12.0 g/mol
O = 3 x g/mol = 48.0 g/mol
H2O = 10 x 18.0 g/mol = 180 g/mol
Formula mass of hydrate = 286 g/mol

11. Step 2: Set up and Calculate
% composition by mass = mass of part/ mass of whole X 100%
% H2O by mass =(180 g/mol)/(286 g/mol) x 100%
% H2O by mass = 62.9 %
How to Calculate % Composition