Percent composition and empirical formula
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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.

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Percent Composition and Empirical Formula

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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

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

B. Examples:

  • 1. Determine the percent composition of the elements in the following compounds:

    • A) H2O

    • B) C6H12O6

    • C) Ba(NO3)2


C practice

C. Practice:

  • A) HF

  • B) NH3


Ii determining empirical formulas from percent composition

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

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 examples1

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

D. Practice

  • Calculate the empirical formula of each of the following substances:

  • 1. A compound is 38.77% Cl and 61.23% O.


D practice1

D. Practice

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


D practice2

D. Practice

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


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