THREE IMPORTANT NUMBERS MOLE MOLAR MASS AVOGADROS NUMBER

THREE IMPORTANT NUMBERS: MOLE, MOLAR MASS, &AVOGADRO'S NUMBER Chapter 12 lesson 1

CHAPTER PREVIEW: Introduces 3 important concepts Useful Take it slowly so everyone understands Will build on them periodically throughout the year

THE MOLE Some familiar concepts What unit do we buy eggs in? What unit do we buy paper in? What unit do we buy shoes in? What unit do we buy bottle rockets in? These are called counting units. Can you think of any more?

THE MOLE !! Concept #1 mole – The number of atoms in exactly 12 grams of carbon 12 The SI unit of amount (mol) 1 mole = 6. 022 x 1023 particles

MOLE The mole is a convenient counting unit for chemists. � 1 mole of carbon � 2 moles of HCl Chemists invented this unit because it is much easier to use in chemical equations and calculations – it is extremely useful Simplifies calculations dealing with amounts of any chemical Allows use of relatively small, simple numbers in most calculations

FOR EXAMPLE: Instead of saying 40. 08 g Ca + 36. 04 g H 2 O → 74. 09 g Ca(OH)2 + 2. 016 g H 2 You can say 1 Ca + 2 H 2 O → 1 Ca(OH)2 + 1 H 2 Yes, those coefficients you use when balancing equations… those are the number of moles! Imagine trying to balance equations using grams!

SILLY EXAMPLE 1 The mole represents a huge number of very tiny particles. Remember 1 mole = 6. 022 x 1023 particles. How big is that? Lets pretend you would measure money that way. If someone were to give away $1 mole, how much money would every one of the roughly 7. 0 billion people on Earth get if they divided it equally?

FACTOIDS 1 mole of periods (. ) placed side by side would equal the radius of the milky way galaxy 1 mole of marbles would cover the entire United States with a layer 70 miles deep So obviously we do not use it for ordinary objects. We only use it to represent tiny particles, such as atoms, electrons, or molecules.

WHAT USE IS IT? If the mole is a counting unit, how do you use it? In equations, formulas, etc. Although the mole is exceptionally helpful in calculations, when you are making measurements in the lab, it must be converted into grams.

MOLAR MASS Concept #2 Molar mass – The mass of one mole of a pure substance (in g/mol) Measuring the mass of the atoms, molecules, or chemical units of a substance Unit is “g/mol” For elements, it just happens to be numerically equal to the average atomic mass in amu.

MOLAR MASS & BBTT Molar mass is used heavily in boom, tap. (Aha! That’s why we learned how to do it!) Ex: If I have 11 moles of sodium, how many grams to I have? Answer = 2. 5 x 102 g

THE THIRD NUMBER… Now that you’re an expert at using Moles and Molar Mass, I’ve got another number for you…

AVOGADRO'S NUMBER Concept #3 Avogadro’s number – The number of particles in exactly one mole of a pure substance: 6. 022 x 1023 particles/mol Surprise! It’s not new at all. It’s the same number used to define the mole! But now we learn to use it to convert from moles to the number of particles.

AVOGADRO’S NUMBER “particles” can mean: Atoms Electrons Protons Grains of sand Tomatoes Chicken Mc. Nugget Happy Meals OK, not usually those last three. But the key thing to remember is: You can use Avogadro’s number to count various tiny particles, but… NEVER use it to count grams. Never!

AVOGADRO'S NUMBER & BBTT Avogadro’s Number (6. 022 x 1023 particles/mole) is also used often in Boom boom, tap. Ex: How many moles of silver are in 3. 01 x 1023 atoms of silver? Answer: 0. 500 mol Ag

EXAMPLE Bob won 11 moles of gold. How many atoms did he win? Answer: 6. 6 x 1024 atoms (about 2. 2 kg!)

ONE MORE FOR THE ROAD… Bonnie has 12 g of Nickel. How many atoms of nickel does she have? Hint, use both the molar mass and Avogadro's number! Answer: 1. 2 x 1023 atoms

ADVICE Many students struggle with deciding when to use Avogadro’s number, the mole, or molar mass. �I just look at the units to decide which to use Look at what units you have, and what units you need. What can you use to cancel units via BBTT to get what you need? Molar mass: grams → moles → grams Avogadro’s #: moles → number of particles → moles The mole is used to count large amounts of particles (just like the dozen is used)