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Percent Composition and Empirical Formula

Percent Composition and Empirical Formula. Chemistry Dr. Davis. A. Percent Composition: the percentage by mass of each element in a compound.

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Percent Composition and Empirical Formula

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  1. Percent Composition and Empirical Formula Chemistry Dr. Davis

  2. A. Percent Composition: the percentage by mass of each element in a compound • 1. Looking at the formula for FeO, we might assume the percent compositions of both elements to be 50%. However, because the percent is based on mass, the percent of Fe is 77.7% and oxygen is 22.3% (Oxygen weighs less)

  3. B. Examples: • 1. Determine the percent composition of the elements in the following compounds: • A) H2O • B) C6H12O6 • C) Ba(NO3)2

  4. C. Practice: • A) HF • B) NH3

  5. II. Determining Empirical Formulas from Percent Composition • A. Empirical Formulas – a chemical formula that shows the composition of a compound in terms of the simplest ratio. • B. Steps • 1. Convert mass percentage of each element to grams • 2. Convert grams to moles using molar mass • 3. Compare amounts of moles to find the simplest whole-number ratios

  6. C. Examples: • 1. Chemical analysis of a liquid shows that it is 60.0% C, 13.4% H, and 26.6% O by mass. Calculate the empirical formula of this substance.

  7. C. Examples • 2. A dead alkaline battery is found to contain a compound of Mn and O. Its analysis gives 69.6% Mn and 30.4% O. Calculate the empirical formula of this substance.

  8. D. Practice • Calculate the empirical formula of each of the following substances: • 1. A compound is 38.77% Cl and 61.23% O.

  9. D. Practice • 2. Magnetic iron oxide is 72.4% iron and 27.6% oxygen.

  10. D. Practice • 3. A liquid compound is 18.0% C, 2.26% H, and 79.7% Cl.

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