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Lesson Objective

Lesson Objective. I will be able to explain what a “mole” in chemistry means!. Analogy: Think of the term dozen. How many doughnuts are in a dozen?. How many eggs are in a dozen?. How many bricks are in a dozen?. How many ostriches are in a dozen?. Analogy: Think of the term dozen. 12.

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Lesson Objective

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  1. Lesson Objective I will be able to explain what a “mole” in chemistry means!

  2. Analogy: Think of the term dozen... How many doughnuts are in a dozen? How many eggs are in a dozen? How many bricks are in a dozen? How many ostriches are in a dozen?

  3. Analogy: Think of the term dozen... 12 12 12 12

  4. Like a dozen, a mole is a set number of things… Instead of 12 things, a mole is 6.02 x 1023things.

  5. One mole is 6.02 x 1023 = 602,000,000,000,000,000,000,000 Or Six hundred and two sextillion of whatever you are counting.

  6. The Mole Introduction • Why do scientists need a unit like the mole? • Atoms and molecules are too small to see. • The mole allows scientists to determine the number of atoms or molecules by weighing and then calculating rather than counting.

  7. The Mole Introduction • Example: There are 6.02 x 1023 molecules of water in 18 ml (about 3 spoonfuls). How long do you think it would take to count that many molecules? • If you guessed “my whole life” you are pretty much correct. Science would get no where if this was necessary.

  8. What is the mole? (Notes) • A mole is the number of atoms in 12 grams of carbon-12. • There are 6.022 x 1023 atoms in 12 grams of carbon-12. • 1 mole (mol) = 6.022 x 1023 particles.

  9. 1 mole (mol) = 6.02 x 1023 This number is a constant. The number of particles in 1 mole is called Avogadro’s Number!

  10. 6.02 x 1023 Avocado Avogadro

  11. So one mole of... ...doughnuts is 6.02 x 1023 doughnuts ... Ostriches is 6.02 x 1023 ostriches ...oxygen atoms is 6.02 x 1023 atoms of oxygen (O) ...oxygen molecules is 6.02 x 1023 molecules of oxygen (O2)

  12. Review- The mole - MEMORIZE • 1 mole = 6.02 x 1023 particles • 6.02 x 1023 is called Avogadro’s number • The periodic table is based on the molar mass of carbon (C)

  13. THE MOLE -- Why? • Why is the mole useful to us as chemists?? • Make a dot on your paper with your pencil. • Guess how many atoms of Carbon graphite are in that dot. • 25 million atoms in that tiny dot!

  14. Say it! • How many particles are in 1 mole? • 6.02 x 1023 • How many atoms are in 1 mole of carbon? • How many atoms are in 1 mole of sodium? • How many atoms are in 1 mole of helium? • How many ducks are in 1 mole of ducks?

  15. Conversions MOLES particles

  16. How many particles are in 1 mole of something? 6.02 x 1023 To convert from number of moles to number of particles, multiply the number of moles by the conversion factor: 6.022 x 1023 1 mol

  17. Example 1: moles to particles • How many particles are in 2.00 moles? • Multiply 2.00 mol x 6.022 x 1023 particles = 12.04 x 1023 particles 1.00 mol 12.04 x 1023= 1.204 x 1024 particles Hint: The unit mol cancels out. Hint: When multiplying with scientific notation, multiply the whole numbers together and just add the 10 base exponent to the answer. Here, multiply (2.00)(6.022) = 12.04. Then, just tack on the x 1023 to the answer. Finally, readjust the decimal point and exponent for proper scientific notation. Here, move the decimal one to the left and increase the exponent by one.

  18. How many particles are in 1 mole of something? 6.02 x 1023 To convert from number of particles to number of moles, multiply the number of moles by the conversion factor: 1 mol___ 6.022 x 1023

  19. Example 2: particles to moles • How many moles is 3.01 x 1022 atoms? • Multiply (3.01 x 1022 atoms) x __1.00 mole = 0.5 x 10-1 mole 6.022 x 1023 atoms Proper scientific notation: 0.5 x 10-1 mole = 5.0 x 10-2 mole Hint: Set up the conversion factor so the unit “atoms” cancels out. Hint: When dividing scientific notation, divide the coefficients first. Here, divide 3.01/6.022 = 0.5. Then, subtract the base 10 exponents. Here 22-23 = -1. Finally, readjust the decimal point and exponent for proper scientific notation. Here, move the decimal one to the right and decrease the exponent by one.

  20. More Practice • How many molecules of HBr are in 2.00 mole of HBr? • How many atoms of gold are in 4 moles of gold? • A sample of hydrochloric acid contains 1.204 x 1024 molecules. How many moles of hydrochloric acid is this? • Which has more atoms: A mole Platinum or a mole of tin?

  21. More Practice Answers • How many molecules of HBr are in 2.00 mole of HBr? 2.00 mol x 6.02 x 1023 (molecules/mol) = 1.204 x 1024 molecules. • How many atoms of gold are in 4 moles of gold? 4.00 mol x 6.02 x 1023(atoms/mol) = 2.408 x 1024atoms. • A sample of hydrochloric acid contains 1.204 x 1024 molecules. How many moles of hydrochloric acid is this? 1.204 x 1024 molecules = 2 mol 6.02 x 1023 molecules/mol • Which has more atoms: A mole Platinum or a mole of tin? Trick question. They have the same number of atoms. Avogadro’s number. 6.02 x 1023.

  22. Random Mole Facts! • Since the Earth has a radius of about 6400 km, its volume is approximately 1021 m3. Since about 500 large grapefruit will fit in one cubic meter, it therefore follows that a mole of grapefruit would have approximately the same volume as the Earth. •  If you had exactly one mole of sheets of paper, you could make one million equal stacks from sea level on the earth that would pass the sun.  • If you had a mole of pennies, you could give out enough money to everyone in the world so that they could spend a million dollars every hour, day and night, for the rest of their lives.

  23. Mole Demonstration… • These pictures all show 1 mole of various substances. Does there seem to be the same volume or mass of the substances? Why or why not? • Answer: No. The number of particles is the same: 6.02 x 1023. But the masses and volumes are different. The mass of one mole of a substance is called its molar mass. This differs depending on the chemical formula of the substance.

  24. Introduction to Molar Mass • Think Pair Share… • How much does a dozen weigh? • Which has more mass, a dozen pencils or a dozen paper clips? “A dozen” does not have a specific mass. We need to know what we are counting first. A mole is similar!

  25. Introduction to Molar Mass Think, Pair, Share! • What is the mass of one mole? • That’s a trick question. The question should be, “What is the mass of one mole of ______________.” Not this kind of mole!!!

  26. What is molar mass? • Why do we care? We need to measure moles of reactants to perform chemical reactions! • The molar mass of an element is the mass of exactly one mole of that element. • The molar mass is the same number as the atomic mass. Just change the units from a.m.u to grams/mole (g/mol). • Let’s check out a periodic table: http://www.webelements.com/

  27. Molar Mass Practice • Use your periodic table to find the molar mass of: • Sodium Na • Chlorine Cl • Carbon C • Hydrogen H • Oxygen O

  28. Molar Mass Practice: Answers • Use your periodic table to find the molar mass of: • Sodium Na = 22.99 g • Chlorine Cl = 35.45 g • Carbon C = 12.01 g • Hydrogen H = 1.01 g • Oxygen O = 16.00 g

  29. Molecular Weight Practice • The molecular weight is simply the sum of the molar masses of atoms in a molecule or compound • Example: The molecular weight of water (H2O) is 18 g. That is 1 g + 1 g + 16 g. • Practice: Find the molecular weight of: • NaCl; CH4; LiF; MgF2

  30. Molecular Weight Practice Answers Practice: Find the molecular weight of: • NaCl= 22.99 g + 35.45 g = 58.44 g • CH4 = 12.01 g + (1.01 g)(4) = 16.05 g • LiF = 6.94 g + 19.00 g = 25.94 g • MgF2 = 24.31 g + (19.00 g)(2) = 62.31 g

  31. Textbook Connections • Read textbook pp. 230-233 • What is a mole? pp. 233 #1, 2, 4, 5, 6(a), 8(a) • Read textbook pp. 230, 236-240 • pp. 233 #6(b, c, d), 7(c), 8(b) • Molar mass: pp. 233 #11, pp. 240 #5 & 10(a, b, c, & e)

  32. Answers pp. 233 #1, 2, 4, 5, 6(a), 8(a)  1. A mole is the number of atoms in exactly 12 g of carbon-12. 2. There are 6.022 x 1023 particles in one mole. “Particles” refers to atoms, ions, or molecules. • 1 mol of nickel(II) and 1 mol of nickel(III) both contain exactly 6.022 x 1023 ions. • (This is like asking “which is heavier: 1 pound of feathers or a 1 pound brick?” They are both 1 pound! Similarly, 1 mol of anything always contains 6.022 x 1023 of whatever is being counted.) • 1.11 mol Pt is more than 6.022 x 1023 atoms. • (This is the same as asking whether 1.11 is more or less that 1.00 because 1.00 mol = 6.022 x 1023 particles. 1.11 is more than 1.00.)

  33. HW Review Continued… • 6(a). 1.204 x 1024 ions Fe3+ • 8(a). 0.500 mol H2O • We will work through how to answer these questions in today’s lesson!

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