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PERCENT COMPOSITION

Learn about the law of definite proportions and how to calculate percentage composition of elements in compounds through examples and formulas. Discover how to determine the mass percentage of elements like hydrogen, zinc, sulfur, carbon, hydrogen, and oxygen in chemical compounds using molar mass and calculations.

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PERCENT COMPOSITION

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  1. PERCENT COMPOSITION Section 6.1

  2. THE LAW OF DEFINITE PROPORTIONS • The elements in a chemical compound are always present in the SAME proportions by mass • Ex: H2O: the proportion of Hydrogen and Oxygen stays constant

  3. MASS PERCENT OF AN ELEMENT % Composition = Mass of element x 100% Mass of compound

  4. MASS PERCENT OF AN ELEMENT • Mass percent of hydrogen in water: • Mass of H2 = 2 (1.01) = 2.02 g/mol • Mass of H2O= 18.02 g/mol (Molar mass) • % mass of H2 = mass of H2 100% • mass of H2O = 2.02 g/mol x 100% 18.02 g/mol = 11.2 %

  5. PERCENT COMPOSITION • Tells you the masspercent (%) of all elements in a molecule

  6. PERCENT COMPOSITION Ex 1: A compound with a mass of 48.72 g is found to have 32.69 g of zinc and 16.03g of sulfur. What is the percent composition of the compound? Given: Mass of compound 48.72 g Mass of Zn = 32.69 g Mass of S = 16.03 g

  7. PERCENT COMPOSITION • % Zn = 32.69g x 100% 48.72g • % S = 16.03g x 100% 48.72g = 67.10% = 32.9%

  8. PERCENT COMPOSITION • Can also be calculated using the chemical formula • Ex 2: What is the % composition of each of the elements in C9H8O? • = 9(12.01g/mol) + 8(1.01g/mol) + 16g/mol = 108.09 + 8.08 + 16 = 132.17g/mol

  9. PERCENT COMPOSITION • % C = 108.09 g x 100% 132.17g = 81.78 % • % H = 8.08g x 100% 132.17 g = 6.11 % • % O = 16.00g x 100% 132.17 g = 12. 10%

  10. PERCENT COMPOSITION • Sometimes chemists use % composition when they have unknown compounds to determine the mass of the elements that make up the compound

  11. HOMEWORK • READ Section 6.1 • Page 260: # 1-9 • Page 264: # 11-18 • Page 266: # 21-30

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