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Understanding the Mole: The Essential Unit of Chemical Measurement

The mole is a fundamental unit in chemistry that allows us to quantify particles, such as atoms and molecules. Much like a dozen indicates a quantity of 12, a mole represents approximately 6.02 x 10^23 particles, known as Avogadro's Number. This concept simplifies the measurement of atomic scales to a more practical level for laboratory use. For example, the atomic mass of an element, expressed in grams, equals one mole of that element. Discover how to use the mole to calculate quantities in chemistry efficiently.

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Understanding the Mole: The Essential Unit of Chemical Measurement

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  1. TheMole Unit 3

  2. The Mole • So far we have been dealing with numbers on the atomic scale… • Atomic Number = # of protons • Mass Number = # of protons + # of neutrons • Atomic Mass = # of amu in one average atom

  3. The Mole • This is a really small scale. • Is it logical to try to measure out chemicals for labs this way? • NO! • We need a bigger scale to use for everyday measurements and calculations.

  4. The Mole • We need… • The MOLE! • The MOLE is a unit of measure – a unit of “how many”.

  5. The Mole • Just like a dozen eggs tells us “how many” eggs, a mole tells us “how many” particles. • 1 dozen eggs = 12 eggs • 1 mole = 6.02 x 1023 particles • Particles can be anything – atoms, molecules, eggs, etc.

  6. The Mole • This number (6.02 x 1023) is called Avogadro’s Number, in honor of Amedeo Avogadro’s contributions to chemistry. • Unfortunately for him, his ideas weren’t really recognized as important until after he died.

  7. The Mole • But wait, where did we get this number? • Scientists have found that there is exactly 1 mole of atoms in the atomic mass of an element when that mass is expressed in grams. • Huh?

  8. The Mole • For example: • What is the atomic mass of C-12? • (Hint – there is only one isotope here, so think mass number) • Atomic mass = 12 amu

  9. The Mole • Then express that mass in grams  12 g • In exactly 12 grams of C-12, there is one mole (6.02 x 1023) of atoms. • This also works for our average atomic masses (from the periodic table).

  10. The Mole • So, in exactly 12.01 g of natural carbon there are 6.02 x 1023 atoms. • AND, 6.02 x 1023 atoms = 1 mole. So 1 mole of carbon = 12.01 g. • Hmm…..those sounds suspiciously like conversion factors… • Time for examples!

  11. The Mole • How many atoms are in 1.00 mole of gold? 6.02 x 1023 atoms 6.02 x 1023 Atoms Au 1.00 mole Au = 1 mole

  12. The Mole • How many molecules are in 2.00 moles of water? 6.02 x 1023 molecules 1.20 x 1024 Molecules H2O 2.00 mole H2O = 1 mole

  13. The Mole • How many marbles are in 1.00 mole of marbles? (Enough to cover the entire Earth to a depth of 50 miles!) 6.02 x 1023 marbles 1.00 mole marbles = 1 mole 6.02 x 1023 marbles

  14. The Mole • How many grams are in 1.00 mole of neon? 6.02 x 1023 atoms 20.18 g Ne 1.00 mole Ne 1 mole Ne 6.02 x 1023 atoms = 20.2 g Ne

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