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Unit 5 The Mole—Counting Molecules

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1 Unit 5 The Mole—Counting Molecules

2 Section 1: Part A Counting Molecules What is a Mole? Ted Ed video

3 What is a Mole? Mole – metric unit for counting particles
We use it just like we use the terms dozen and ream! The only acceptable abbreviation for “mole” is “mol”…not “m”!!

4 What is a counting unit? You’re already familiar with one counting unit…a “dozen” A dozen = 12 “Dozen” 12 A dozen doughnuts 12 doughnuts A dozen books 12 books A dozen cars 12 cars

5 What can’t we count atoms in “dozens”?
Atoms and molecules are extremely small We use the MOLE to count particles

6 A mole = 6.02  1023 particles (called Avogadro’s number)
6.02  1023 = 602,000,000,000,000,000,000,000 “mole” 6.02  1023 1 mole of doughnuts 6.02  1023 doughnuts 1 mole of atoms 6.02  1023 atoms 1 mole of molecules 6.02  1023 molecules This number was named after Amadeo Avogadro. He did not calculate it!

7 FUNNY!

8

9 Representative Particles
Remember, matter is broken down into either SUBSTANCES or mixtures Substances are broken down into either ELEMENTS or COMPOUNDS Type of Matter Example Representative Particle Element Cu Atom Ionic Compound CuCl2 Formula Unit Covalent Compound CO Molecule Diatomic Element Cl2

10 Steps to Solving Mole Conversions
Identify the known, given amount/unit & the unknown desired unit in the problem 2. Write down the given amount and unit on paper and draw a t-chart 3. Place the given unit in the denominator & the desired unit in the numerator 4. Find a conversion factor that relates given units to desired units. Match the numbers in the conversion factor to their respective units. 5. Cancel out any units that are identical on top and bottom. Do the math 6. Don't forget significant figures and units in final answer

11 Convert 15 moles of Cu into atoms
Example: Particles & Moles Use the conversion factor (1 mol = 6.02 x 1023) particles to convert Example 1: Convert 15 moles of Cu into atoms

12 Example: Molecules & Moles
Convert 15 moles of Cu into atoms 1 mol = 6.021023 molecules 15 mol Cu atoms Cu 6.02  1023 = _______ atoms H2O 9.031024 1 mol Cu

13 Convert 3.8 × 1014 molecules of CO to moles?
Let’s Practice #2 Example: Convert 3.8 × 1014 molecules of CO to moles?

14 Convert 3.8 x1014 molecules of CO to moles?
Let’s Practice #2 Example: Convert 3.8 x1014 molecules of CO to moles? 1 mol = 6.021023 formula units 3.8 × 1014 molecules 1 mole = _______ moles 6.31 x 10-10 6.02  1023 molecules

15 Convert 7.8 mol LiCl to formula units.
Let’s Practice #3 Example: Convert 7.8 mol LiCl to formula units.

16 Convert 7.8 mol LiCl to formula units.
Let’s Practice #3 Example: Convert 7.8 mol LiCl to formula units. 1 mol = 6.021023 molecules 7.8 moles LiCl 6.02 x 10 23 Formula units = _______ formula units 4.70 x 1024 1 moles LiCl

17 Section 1: Part C Molar Mass Conversions
Molar Mass – The mass for one mole of an atom or molecule. Other terms commonly used for the same meaning: Molecular Weight Molecular Mass Formula Weight Formula Mass

18 Molar Mass for Elements
The average atomic mass = grams for 1 mole Average atomic mass is found on the periodic table Element Mass 1 mole of carbon atoms (C) 12.01 g 1 mole of oxygen atoms (O2) 16.00 g x 2 = g O2 1 mole of hydrogen atoms (H2) 1.01 g x 2 = 2.02 g H2 Unit for molar mass: g/mole or g/mol

19 Molar Mass for Compounds
The molar mass for a molecule = the sum of the all the atomic masses of each atom within the compound

20 Calculating a Molecule’s Mass
To find the molar mass of a molecule: 1 Count the number of each type of atom 2 Find the molar mass of each atom on the periodic table 3 Multiply the # of atoms by the molar mass for each atom 4 Add the masses up!

21 Find the molar mass for CaBr2
Example: Molar Mass Example: Find the molar mass for CaBr2

22 Find the molar mass for CaBr2
Example: Molar Mass 1 Count the number of each type of atom Example: Find the molar mass for CaBr2 Ca 1 Br 2

23 Find the molar mass for CaBr2
Example: Molar Mass 2 Find the molar mass of each atom on the periodic table Example: Find the molar mass for CaBr2 Ca 1 40.08 g/mole Br 2 79.90 g/mole

24 Find the molar mass for CaBr2
Example: Molar Mass 3 Multiple the # of atoms  molar mass for each atom Example: Find the molar mass for CaBr2 Ca 1 40.08 g/mole = 40.08 g/mole Br 2 79.90 g/mole = g/mole

25 Find the molar mass for CaBr2
Example: Molar Mass 4 Find the sum of all the masses Example: Find the molar mass for CaBr2 Ca 1 40.08 g/mole = 40.08 g/mole Br 2 79.91 g/mole = + g/mole g/mole 1 mole of CaBr2 = g

26 Example 2: If you see a Parentheses in the Formula
Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis. Example: Find the molar mass for Sr(NO3)2

27 Example 2: Molar Mass & Parenthesis
Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis. Example: Find the molar mass for Sr(NO3)2 Sr 1 87.62 g/mole = 87.62 g/mole N 2 14.01 g/mole = 28.02 g/mole O 6 16.00 g/mole = + 96.00 g/mole g/mole 1 mole of Sr(NO3)2 = g

28 Find the molar mass for Al(OH)3
Let’s Practice #3 Example: Find the molar mass for Al(OH)3

29 Find the molar mass for Al(OH)3
Let’s Practice #2 Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis. Example: Find the molar mass for Al(OH)3 Al 1 26.98 g/mole = 26.98 g/mole O 3 16.00 g/mole = 48.00 g/mole H 3 1.01 g/mole = + 3.03 g/mole 78.01 g/mole 1 mole of Al(OH)3 =78.01 g

30 Using Molar Mass in Conversions
What is molar mass?

31 Using Molar Mass in Conversions: Example: Moles to Grams
How many grams are in 1.25 moles of water?

32 Example: Moles to Grams
When converting between grams and moles, the molar mass is needed Example: How many grams are in 1.25 moles of water? H O 2 1 1.01 g/mole 16.00 g/mole = 2.02 g/mole + 18.02 g/mole 1 mole H2O molecules = g 1.25 mol H2O 18.02 g H2O = _______ g H2O 22.5 1 mol H2O

33 Example: Grams to Moles
How many moles are in 25.5 g NaCl?

34 Example: Grams to Moles
How many moles are in 25.5 g NaCl Na Cl 1 22.99 g/mole 35.45 g/mole = + 58.44 g/mole 1 moles NaCl molecules = g 25.5 g NaCl 1 mol NaCl 58.44 g NaCl = ____ moles NaCl .436

35 Example: Grams to Molecules
How many formula units are in 25.5 g NaCl?

36 Example: Grams to Moles
How many formula units are in 25.5 g NaCl Na Cl 1 22.99 g/mole 35.45 g/mole = + 58.44 g/mole 1 moles NaCl formula units = g 25.5 g NaCl 1 mol NaCl 6.02 x 1023 FU’s 58.44 g NaCl 1 mol NaCl 2.63 x 1023 = ____ FU’s NaCl

37 Section 1: Part D Gases & Moles
Amounts

38 Molar Volume The molar volume of a gas is measured at
STP (standard temperature and pressure) 1 mole of any gas = 22.4 L

39 Molar Volume as a Conversion Factor
The molar volume at STP has about the same volume as 3 basketballs can be used to form 2 conversion factors: 22.4 L and mole 1 mole L

40 Let’s Try it Out! Example
When converting between volume and moles, STP must be a condition to use molar volume Example: An experiment requires .0580 moles of NO. What volume would you need at STP? 1 mole NO = 22.4 L .O580 mol NO 22.4 L NO = _______ L NO 1.2992 1 mol NO

41 Suppose you need 4.22 g of Cl2. What volume at STP would you use?
Try Another! Example: Suppose you need 4.22 g of Cl2. What volume at STP would you use? 1 moles Cl2 = g Cl2 1 mol = 22.4 L at STP 4.22 g Cl2 1 L Cl2 mol Cl2 22.4 70.90 g Cl2 1 mol Cl2 = _________ L Cl2 1.33

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