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Percentage Composition: Calculation and Examples

Learn how to calculate the percentage composition of compounds using their formula and experimental mass analysis. Includes step-by-step examples.

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Percentage Composition: Calculation and Examples

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  1. 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

  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 58.44 g/mol • There is 1 atom of Na in each NaCl formula unit • The molar mass of Na is 22.99 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 = (12.01 + 1.01 + 3 × 35.45)g/mol = 119.37g/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 = (12.011 + 1.00797 + 3 × 35.453)g = 119.377g 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 = (12.011 + 1.01 + 3 × 35.45)g = 119.37g 1(M) %C = ------------ × 100% MCHCl3 1(12.01) %C = -------------- × 100% = 10.061% 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 = (12.01 + 1.01 + 3 × 35.45)g = 119.37g 1(1.01) %H = -------------- × 100% = 0.846109% 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 = (12.01 + 1.01 + 3 × 35.45)g = 119.37g 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 = 119.37g %C = 10.061% C = 10.06% C %H = 0.846109% H = 0.85% H %Cl = 89.093% Cl = 89.09% 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.

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