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Percent Composition and Empirical Formula

Percent Composition and Empirical Formula. Third week. Percent Composition. % is based on the mass of an item That is Grams to the rest of you! The equation is: Mass of item X 100 Total Mass Molar mass may be used to calculate % composition. Answer. 2 Cl = 2 (35.5) = 71 amu

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Percent Composition and Empirical Formula

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  1. Percent Composition and Empirical Formula Third week

  2. Percent Composition • % is based on the mass of an item • That is Grams to the rest of you! • The equation is: Mass of item X 100 Total Mass • Molar mass may be used to calculate % composition.

  3. Answer • 2 Cl = 2 (35.5) = 71 amu • 2 F = 2 (19) = 38 amu • 1 C = 1 (12) = 12 amu • Molar mass = 121 g/mol • % comp or % mass of Cl in compound = (71/121)x100=58.68

  4. What is the percent mass of oxygen in Ascorbic Acid?

  5. Answer: • 6 Carbons = 72 amu • 8 Hydrogens = 8 amu • 6 Oxygens = 96 amu • Molar mass = 176 g/mol • % composition = (96/176) X100 = 54.55

  6. Empirical Formula • Empirical Formula is the ratio of moles of the elements that are contained in a substance (ionic or molecular). • OR is the lowest whole number ratio of a chemical formula. Remember: • Chemical Formula gives the actual ratio of elements in a chemical.

  7. Using % Composition to calculate Empirical Formula • First- find the % composition of each element. • Second- assume a sample of 100 grams • Third- find the grams of each element • Fourth- convert grams to moles • Fifth- Calculate mole ratio. Divide all moles by the smallest number of mole to make the smallest equal to one. Round all to the closest whole number.

  8. Determining the molecular formula from the Empirical Formula • You can determine the molecular formula if you know the empirical formula and the molar mass. • Find the empirical molar mass. • Divide it by the molar mass. • Multiply the subscripts of the empirical formula by the quotient. • Worksheet

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