6.02 X Lesson # 9.1: The Mole. Unit 9: Math of Chemistry Chemical Quantities Part I. Yes, you will need a calculator for this chapter!

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1: The Mole Yes, you will need a calculator for

1: The Mole: A Measurement of Matter OBJECTIVES:

1 Unit 9: Math of Chemistry Chemical Quantities Part I Lesson # 9.1: The Mole Yes, you will need a calculator for this chapter! The Mole 6.02 X Lesson 9.1: The Mole: A Measurement of Matter OBJECTIVES: Describe methods of measuring the amount of something. Define Avogadro s number as it relates to a mole of a substance. Lesson 9.1: The Mole: A Measurement of Matter OBJECTIVES: Distinguish between the atomic mass of an element and its molar mass. Describe how the mass of a mole of a compound is calculated. How do we measure items? You can measure mass. or volume.. or you can count pieces in grams. in liters. in MOLES. What is the mole? We re not talking about this kind of mole! 1

Moles (is abbreviated: mol) It is an amount (or a counting unit), defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole = 6.02 x 10 23 of the representative particles.

Amedeo Avogadro (1776 1856), Similar Words for an amount Counting Units Pair: 1 pair of shoelaces = 2 shoelaces Dozen: 1 dozen oranges = 12 oranges Gross: 1 gross of pencils = 144 pencils Ream: 1

2 Moles (is abbreviated: mol) It is an amount (or a counting unit), defined as the number of carbon atoms in exactly 12 grams of carbon mole = 6.02 x of the representative particles. Treat it like a very large dozen 6.02 x is called: Avogadro s number. Amedeo Avogadro ( ), Similar Words for an amount Counting Units Pair: 1 pair of shoelaces = 2 shoelaces Dozen: 1 dozen oranges = 12 oranges Gross: 1 gross of pencils = 144 pencils Ream: 1 ream of paper = 500 sheets of paper The Mole 1 dozen cookies = 12 cookies 1 mole of cookies = 6.02 X cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 X cars 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6.02 X atoms Note that the NUMBER is always the same, but the MASS is very different! Mole is abbreviated mol (gee, that s a lot quicker to write, huh?) 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. Learning Check Suppose we invented a new collection unit called a comet. One comet contains 8 objects. 1. How many paper clips in 1 comet? a) 1 b) 4 c) 8 2. How many oranges in 2.0 comet? a) 4 b) 8 c) How many comets contain 40 gummy bears? a) 5 b) 10 c) 20 What are Representative Particles? The smallest pieces of a substance: 1) For a molecular compound: it is the molecule. 2) For an ionic compound: it is the formula unit (made of ions). 3) For an element: it is the atom. Remember the 7 diatomic elements? ( they are the exception - made of molecules) 2

3 A Mole of Particles Contains 6.02 x particles 1 mole C 1 mole H 2 O 1 mole NaCl = 6.02 x C atoms = 6.02 x H 2 O molecules = 6.02 x NaCl formula units (technically, ionics are compounds not molecules so they are called formula units) 6.02 x Na + ions and 6.02 x Cl ions Avogadro s Number as Conversion Factor 6.02 x particles 1 mole or 1 mole 6.02 x particles Note that a particle could be an atom OR a molecule! Learning Check 1. How many atoms of Al are in mole of Al a) 500 Al atoms b) 6.02 x Al atoms c) 3.01 x Al atoms 2.How many moles of S in 1.8 x S atoms a) 1.0 mole S atoms b) 3.0 mole S atoms c) 1.1 x mole S atoms Types of questions How many oxygen atoms in the following? CaCO 3 atoms of oxygen 3 Al 2 (SO 4 ) 3 How many ions in the following? CaCl 2 NaOH Al 2 (SO 4 ) 3 12 (3 x 4) atoms of oxygen 3 total ions (1 Ca 2+ ion and 2 Cl 1- ions) 2 total ions (1 Na 1+ ion and 1 OH 1- ion) 5 total ions (2 Al SO 4 2- ions) Practice problems (round to 3 sig. figs.) How many molecules of CO 2 are in 4.56 moles of CO 2? 2.75 x molecules How many moles of water is 5.87 x molecules? mol (or 9.75 x 10-2 ) How many atoms of carbon are in 1.23 moles of C 6 H 12 O 6? 4.44 x atoms C How many moles is 7.78 x formulaunits of MgCl 2? 12.9 moles Measuring Moles Remember relative atomic mass? - The amu was one twelfth the mass of a carbon-12 atom. Since the mole is the number of atoms in 12 grams of carbon-12, the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams. 3

4 Gram Atomic Mass (GAM) Equals the mass of 1 mole of an element in grams, or, to the numerical value of the average atomic mass (get from periodic table) grams of C has the same number of pieces as grams of H and grams of iron. We can write this as: g C = 1 mole C (this is also the molar mass) We can count things by weighing them. 1 mole of C atoms = 12.0 g 1 mole of Mg atoms = 24.3 g 1 mole of Cu atoms = 63.5 g Other Names Related to Molar Mass Molecular Mass/Molecular Weight: If you have a single molecule, mass is measured in amu s instead of grams. But, the molecular mass/weight is the same numerical value as 1 mole of molecules. Only the units are different. (This is the beauty of Avogadro s Number!) Gram Formula Mass/Formula Weight: Same goes for compounds. But again, the numerical value is the same. Only the units are different. THE POINT: You may hear all of these terms which mean the SAME NUMBER just different units Find the molar mass (usually we round to the tenths place) A. 1 mole of Br atoms = 79.9 g/mole B. 1 mole of Sn atoms = g/mole What about compounds? in 1 mole of H 2 O molecules there are two moles of H atoms and 1 mole of O atoms (think of a compound as a molar ratio) To find the mass of one mole of a compound determine the number of moles of the elements present Multiply the number times their mass (from the periodic table) add them up for the total mass Calculating Gram Formula Mass (GFM) Calculate the formula mass of magnesium carbonate, MgCO g + 12 g + 3 x (16.00 g) = 84.3 g Thus, 84.3 grams is the formula mass for MgCO 3. 4

A. Molar Mass of K 2 O =? Grams/mole 94.20 g/mol B. Molar Mass of antacid Al(OH) 3 =? Grams/mole 78.01 g/mol C. Molar Mass of Al 2 (SO 4 ) 3 =? Grams/mole 342.

5 A. Molar Mass of K 2 O =? Grams/mole g/mol B. Molar Mass of antacid Al(OH) 3 =? Grams/mole g/mol C. Molar Mass of Al 2 (SO 4 ) 3 =? Grams/mole g/mol Learning Check Prozac, C 17 H 18 F 3 NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. Find its molar mass g/mol Calculations with Molar Mass molar mass Grams Moles The mole road map shows the conversion factors needed to interconvert between mass, number of particles, and volume of a gas at STP. The mole is the at the center of any calculation involving Converting Moles and Grams Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al? g Al 1. Molar mass of Al 1 mole Al = 27.0 g Al 2. Conversion factors for Al 27.0g Al or 1 mol Al 1 mol Al 27.0 g Al 3. Setup 3.00 moles Al x 27.0 g Al 1 1 mole Al Answer = 81.0 g Al 5

Atoms/Molecules and Grams The artificial sweetener aspartame (Nutra- Sweet) formula C 14 H 18 N 2 O 5 is used to sweeten diet foods, coffee and soft drinks.

(Two step process) You can t go directly from atoms to grams!!!! You MUST go thru MOLES. That s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz?

6 Atoms/Molecules and Grams The artificial sweetener aspartame (Nutra- Sweet) formula C 14 H 18 N 2 O 5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? Since 6.02 X particles = 1 mole AND 1 mole = molar mass (grams) You can convert atoms/molecules to moles and then moles to grams! (Two step process) You can t go directly from atoms to grams!!!! You MUST go thru MOLES. That s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first! Calculations use molar mass use Avogadro s number Grams Moles particles Everything must go through Moles!!! Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 X 1 mol g Cu X = 3.4 X atoms Cu 6.02 X atoms Cu 1 mol Cu How many atoms of K are present in 78.4 g of K? What is the mass (in grams) of 1.20 X molecules of glucose (C 6 H 12 O 6 )? 6

How many atoms of O are present in 78.1 g of oxygen? 78.1 g O 2 1 mol O 2 6.

1 grams C How many moles of magnesium is 24.31 g of Mg?

7 How many atoms of O are present in 78.1 g of oxygen? 78.1 g O 2 1 mol O X molecules O 2 2 atoms O 32.0 g O 2 1 mol O 2 1 molecule O 2 Examples How much would 2.34 moles of carbon weigh? 28.1 grams C How many moles of magnesium is g of Mg? 1 mol Mg How many atoms of lithium is 1.00 g of Li? 8.72 x atoms of Li How much would 3.45 x atoms of U weigh? 13.6 grams U Any Questions? What now? 39 7

The Mole. Chapter 7 Homework. Page 175 # s 5 & 6 Page 179 # s 7 & X 10 23

The Mole. Chapter 7 Homework. Page 175 # s 5 & 6 Page 179 # s 7 & X 10 23 The Mole 1 Chapter 7 Homework Page 175 # s 5 & 6 Page 179 # s 7 & 8 6.02 X 10 23 2 The Mole A counting unit Similar to a dozen, except instead of 12, it s 602 billion trillion 602,000,000,000,000,000,000,000