Mole Notes

Stoichiometry –

  • the study of the quantitative aspects of chemical reactions

The mole –

  • A counting unit
  • Similar to a dozen, except instead of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000
  • 6.02 X 10 to the 23 power (in scientific notation)

How big is the Mole?

  • Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.
  • If you had Avogadro’s number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to the of over 9 miles.
  • If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

Where did it come form?

  • It was NOT just picked. It was MEASURED
  • One of the better methods of measuring this number was the Millikan Oil Drop Experiment
  • Since then we have found even better ways of measuring using x-ray technology

The Mole

  •  1 dozen cookies= 12 cookies
  • 1 mole of cookies = 6.02 X 10 to the 23 power cookies
  • 1 dozen cars = 12 cars
  • 1 mole of cars = 6.02 X 10 to the 23 power cars
  • 1 dozen Al atoms= 12 Al atoms
  • 1 mole of Al atoms =6.02 X 10 to the 23 power atoms
  • Note that the number is always the same, but the mass is very different.
  • Mole is abbreviated mol

Molar Mass

  • The Mass of 1 mole (in grams)
  • Equal to the numerical value of the average atomic mass
  • 1 mole of C atoms = 12.0 g
  • 1 mole of Mg atoms = 24.3 g
  • 1 mole of Cu atoms = 63.5

Other Name Related to Molar Mass

  • Molecular Mass/ Molecular Weight: If you have a single molecule, mass is measured in amu’s instead of grams. But, the molecular mass/weight is the same numerical value as 1 mole of molecules. Only the units are different.
  • Formula Mass/Formula Weight: Same goes for compounds. But again, the numerical value is the same. Only the units are different.
  • The Point: you may hear all of these terms which mean the same number… just different unites

Converting Moles and Grams

  • Aluminum is often used for the structure of light-weigt bicycle frames.

Types of Formulas

  • Empirical formula: the formula of a compound that expresses the smallest whole number ratio of the atoms present.
  • ionic formula are always empirical formulas.
  • Molecular Formula: the formula that states the actual number of each kind of atom found in one molecule of the compound.

To obtain an Empirical Formula

  1. Determine the mass in grams of each element present, if necessary.
  2. Calculate the number of moles of each element.
  3. Divide each by the smallest number of moles to obtain the simplest whole number ratio.
  4. If whole numbers are not obtained in step 3, multiply through by the smallest number that will give all whole number.
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