1. Percentage Composition
Chapter 6.1
Percentage Composition

2. Percent Composition
Percent composition is the percentage of each element in a compound (by mass)
Percent composition can be determined from either:
the formula of the compound
the experimental mass analysis of the compound
Note: The percentages may not always total to 100% due to rounding 12

3. Combustion Analysis

4. Percent Composition Calculations
To determine Percent Composition from the chemical formula:
Determine the molar mass of compound
Multiply the molar mass of the element of interest by the number of atoms per molecule then
Divide this value by the molar mass of the compound

5. Percent Composition Calculations
Example: The percent composition of sodium in table salt.
The molar mass of NaCl is g/mol
There is 1 atom of Na in each NaCl formula unit
The molar mass of Na is g/mol

6. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?
MCHCl3 = 1(M)C + 1(M)H + 3(M)Cl
= ( × 35.45)g/mol
= g/mol

7. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?
MCHCl3 = 1(M)C + 1(M)H + 3(M)Cl
= ( × )g
= g
1(M)
%C = × 100
MCHCl3

8. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?
MCHCl3 = 1(M)C + 1(M)H + 3(M)Cl
= ( × 35.45)g
= g
1(M)
%C = × 100%
MCHCl3
1(12.01)
%C = × 100% = % C
119.37

9. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?
MCHCl3 = 1(M)C + 1(M)H + 3(M)Cl
= ( × 35.45)g
= g
1(1.01)
%H = × 100% = % H
119.37
= 0.85 % H

10. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?
MCHCl3 = 1(M)C + 1(M)H + 3(M)Cl
= ( × 35.45)g
= g
3(35.45)
%Cl = × 100% = 89.09% Cl
119.37

11. EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?
MCHCl3 = 1(M)C + 1(M)H + 3(M)Cl
= g
%C = % C = 10.06% C
%H = % H = 0.85% H
%Cl = % Cl = % Cl
100.00% total

12. Percent Composition Calculations
Perform the following % Composition calculations:
The % composition of carbon in carbon monoxide
The % composition of oxygen in water
The % composition of chlorine in sodium hypochlorite (NaClO)

13. One Mole of each Substance
Clockwise from top left:
1-Octanol, C8H17OH;
Mercury(II) iodide, HgI2;
Methanol, CH3OH; and
Sulfur, S8.