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What is a Mole in Chemistry? (Chapter 10)

What is a Mole in Chemistry? (Chapter 10). Today’s Learning Objectives. Understand what a mole is in chemistry Know the relationship of Avogadro’s number to the mole Be able to calculate molar mass (molecular weight) of an element and a compound

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What is a Mole in Chemistry? (Chapter 10)

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  1. What is a Mole in Chemistry? (Chapter 10)

  2. Today’s Learning Objectives • Understand what a mole is in chemistry • Know the relationship of Avogadro’s number to the mole • Be able to calculate molar mass (molecular weight) of an element and a compound • * An appreciation for how big Avogadro’s number really is*

  3. What if you had … 2 pairs of shoes = 4 shoes 3 dozen eggs = 36 eggs Do you know how many eggs are in a flat? In a crate? mole Do you know how many carbon atoms are in a _______?

  4. Avogadro’s Number 6.02 X 1023 Do you know how many carbon atoms are in a mole? Do you know how many protons are in a mole? Do you know how molecules of H2O are in a mole? Do you know how many footballs are in a mole?

  5. It’s a big number!!! • It’s 602 billion trillion 602,000,000,000,000,000,000,000 - 6.02 X 1023 (in scientific notation) His most important contribution to chemistry is known as Avogadro’s Law, which states that all gases that are at the same volume, temperature, and pressure contain the same number of molecules. This law allows chemists to calculate the molecular weight of gases, and if the molecular formula is known, the weight of each atom in the gas. Though it was not well received at the time of publication, it was verified by various other scientists after his death. Any chemist will agree that Avogadro’s Law was a massive step forward in the evolution of chemistry. Amedeo Avogadro 1776-1856

  6. How was this number discovered? It had been estimated by several scientists over the years with crude experiments, but in 1911 Robert Millikan did his famous oil drop experiment which determined the charge on a single electron. For years scientists had known the charge on a mole of electrons, so a simple calculation led to Avogadro’s number. Scientific American article about discovery of Avogadros number

  7. Just How Big is a 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 a depth 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.

  8. The Mole • 1 dozen cookies = 12 cookies • 1 mole of cookies = 6.02 X 1023 cookies • 1 dozen cars = 12 cars • 1 mole of cars = 6.02 X 1023 cars • 3 dozen Al atoms = 36 Al atoms • 3 mole of Al atoms = 3 x 6.02 X 1023 atoms Note that the NUMBER is always the same, but the MASS is very different!

  9. Molar Mass (Molecular Weight) • Defined as: mass of 1 mole of element or molecule (in grams) • Equal to the atomic mass from periodic table. Easy!!! 1 mole of C atoms = 12.0 g/mol 1 mole of Mg atoms = 24.3 g/mol 1 mole of Cu atoms = 63.5 g/mol

  10. Learning Check! Find the molar mass (usually we round to the tenths place) = 79.9 g/mole • 1 mole of Br atoms • 1 mole of Sn atoms = 118.7 g/mole

  11. Molar Mass of Compounds Mass in grams of 1 mole of a compound equals the sum of the molar mass of each element in that compound What is the molar mass of CaCl2? Or written in another way …. How much does 1 mole of CaCl2 weigh? CaCl2 = 1 Ca + 2 Cl = 1 x 40.1 g/mol + 2 x 35.5 g/mol = 40.1 g/mol + 71.0 g/mol = 111.1 g/mol

  12. Learning Check! A. Molar Mass of K2O = ? Grams/mole B. MolarMass of antacid (Tums or Rolaids) Al(OH)3 = ? Grams/mole

  13. Cool Down!!!! Prozac (flouxetine), C17H18F3NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. Find its molar mass.

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