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The Mole

Learn how to count common items like nails and chemical compounds using units such as dozens, pounds, and moles. Understand the concept of Avogadro's number and its significance in chemistry.

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The Mole

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  1. The Mole

  2. Common Counting Units • eggs • dozen (12) • paper • ream (500 sheets) • shoes • pair (2) • pencils • gross (144)

  3. Counting Nails by the Pound • I want some nails for a project, but the hardware store sells nails by the pound! • How do I know how many nails I am buying when I buy a pound of nails? • Analogy • How many atoms in a certain mass of an element?

  4. Counting Nails by the Pound A hardware store customer buys 2.60 pounds of nails. A dozen of the nails has a mass of 0.150 pounds. How many nails did the customer buy? Solution map:

  5. Counting Nails by the Pound • The customer bought 2.60 lbs of nails and received 208 nails. He counted the nails by weighing them!

  6. Counting Nails by the Pound • What if he bought a different size nail? • Would a dozen still weight 0.150 lbs? • Would there be 208 nails in 2.60 lbs? • How would this effect the conversion factors?

  7. Chemist’s Counting Units • need a counting unit for atoms and molecules • since they are extremely small • mole = SI unit to measure the amount of a substance (element or compound) • 1 mole = the number of atoms in exactly 12 grams of pure carbon-12

  8. mole • SI base unit to measure the amount of a substance (element or compound)

  9. Counting Atoms by Moles • The number of atoms in 12 grams of Carbon-12 is 6.022 x 1023 and we call this a mole • 1 mole = 6.022 x 1023 things • Like 1 dozen = 12 things

  10. Chemical Packages - Moles • mole = number of atoms in 12 g of C-12 • 1 atom of C-12 weighs exactly 12 amu • 1 mole of C-12 weighs exactly 12 g • The number of atoms in 1 mole is called Avogadro’s Number = 6.0221421 x 1023 • 1 mole of C atoms weighs 12.01 g and has 6.022 x 1023 atoms • the average mass of a C atom is 12.01 amu

  11. Avogadro’s Number Avogadro (1776-1856) • NA = 6.02 x 1023 of anything

  12. Avogadro’s Number • 1 mole = 6.0221367 x 1023 particles • rounded to 6.02 x 1023 particles • particles can be • atoms (elements) • molecules • formula units

  13. One mole of marbles would cover the entire Earth to a depth of fifty miles One mole of hockey pucks would equal the mass of the moon. One mole of rice grains is more than the number of grains of all crops grown since the beginning of time. If one mole of pennies was divided up equally between all the people on Earth, you would have enough money to spend a million dollars every hour, 24 hours a day, for your entire life. When you died, you would have spent less than half of your pennies. How Big Is The Mole?

  14. Vocabulary Word • Avogadro’s number: the number 6.02 x 1023, tells how many pieces (atoms, molecules or formula units) in a mole

  15. Relationship Between Moles and Mass • The mass of one mole of atoms is called the molar mass • The molar mass of an element, in grams, is equal to the element’s average atomic mass (from the Periodic Table), in amu

  16. 1 mole Sulfur 32.06 g 1 mole Carbon 12.01 g Mole and Mass Relationships

  17. Molar Mass • the mass (in grams) of a mole of substance • On your periodic tables • Round to the nearest tenth • Hydrogen is 1.00797  1.0 g/mol Molar Mass is an INTENSIVE property—doesn’t depend on amount

  18. Vocabulary Word • molar mass: mass in grams of a mole any pure substance

  19. Moles of Compounds Too

  20. Molecular Weight of Compounds • the molecular weight of molecules can be calculated by adding up the atomic masses Formula Mass = 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu • since 1 mole of H2O contains 2 moles of H and 1 mole of O Molar Mass = 1 mole H2O = 2(1.01 g H) + 16.00 g O = 18.02 g

  21. Mole Relationships inChemical Formulas • since we count atoms and molecules in mole units, we can find the number of moles of an element in a compound

  22. Converting from moles to particles • use conversion factors • how many roses are in 3.5 dozen? 3.5 dozen  12 roses = 42 roses dozen

  23. mole conversions • how many particles are in 3.50 moles of sucrose? 3.50 moles  6.02 x 1023 particles mole 21.1 x 1023 2.11 x 1024 particles

  24. particle to mole conversions • how many moles are in 4.50 x 1024 atoms of Zn? 4.50 x 1024 atoms  1 mole 6.02 x 1023 atoms 7.48 moles Zn

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