Unit #1Unit #2Unit #3Unit #4Unit #5Unit #6Unit #7Unit #8Unit #9Unit #10
spacerUNIT # 7  
spacerspacerIntroduction
spacerspacerObjectives
spacerspacerReading

spacer7.1 Calculation of
spacerFormula
spacerMass

spacer7.2 Mole
spacerConcept

spacer7.3 Atomic Mass
spacerRevisited

spacer7.4 Calculation of
spacerMolar Mass
spacer
7.5 Calculations
spacerinvolving
spacerAvogadro #

spacerMass to mole conversion and vice-versa
spacermole to number of particles conversion and vice-versa
spacerMass in grams to number of particles conversion
spacer
7.6 Molar Volume
spacerof a Gas
spacerMolar volume calculations
spacer
7.7 Percent
spacerComposition
spacer
7.8 Empirical
spacerFormula

spacer7.9 Empirical
spacerMass to
spacerMolecular
spacerFormula



spacerProblems
spacer1 | 2
| 3 | 4 | 5

Unit #7CALCULATIONS BASED ON FORMULAE

7.8 - Determination of Empirical Formula

In section 7.7, we learned that percent composition establishes the relative proportions of the elements in a compound in terms of mass. From a given chemical formula, we learned to generate a list of percent compositions of the elements that make up the compound.

In this section, we will carry out the opposite task. We will be given the percent compositions of the elements that make up the compound. From that, we will derive the chemical formula of the compound.

For example:

An analysis of a substance shows that it is made up of carbon, hydrogen, and oxygen. The percentage composition of the elements in the compound are determined to be:

  • 39.10 % carbon,
  • 8.77 % hydrogen, and
  • 52.13 % oxygen.

From the above data we can derive the ratio of carbon, hydrogen and oxygen in the substance. We will put it in the form, CxHyOz, where x, y and z are the simplest whole-number ratio of carbon, hydrogen to oxygen of the substance. This chemical formula is called the empirical formula of a substance.

The empirical formula of the above example is C3H8O3*.

 

 


* It should be noted that the empirical formula may or may not be the true chemical formula of the substance. We will examine this in greater detail in section 7.9.


Section 8.5
Calculation of Empirical (Simplest) and Molecular Formulas ..p200

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