Percent Composition and Empirical Formula

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# Percent Composition and Empirical Formula - PowerPoint PPT Presentation

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

Chemistry

Dr. Davis

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)
B. Examples:
• 1. Determine the percent composition of the elements in the following compounds:
• A) H2O
• B) C6H12O6
• C) Ba(NO3)2
C. Practice:
• A) HF
• B) NH3
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
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.
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.
D. Practice
• Calculate the empirical formula of each of the following substances:
• 1. A compound is 38.77% Cl and 61.23% O.
D. Practice
• 2. Magnetic iron oxide is 72.4% iron and 27.6% oxygen.
D. Practice
• 3. A liquid compound is 18.0% C, 2.26% H, and 79.7% Cl.