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PERCENT COMPOSITION

PERCENT COMPOSITION. Section 6.1. THE LAW OF DEFINITE PROPORTIONS. The elements in a chemical compound are always present in the SAME proportions by mass Ex: H 2 O: the proportion of Hydrogen and Oxygen stays constant. MASS PERCENT OF AN ELEMENT. % Composition = Mass of element x 100%

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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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