Unit 5 Section 1: The Mole Concept

Unit 5 Section 1: The Mole Concept

Lesson Objectives

• Review Ideas for converting between two units

• Understand the concept of a mole

• Relate Moles to Grams and molar mass

• Calculating the Molar Mass of Compounds

• Converting between moles and Various Units

Measuring Matter

• Chemistry is a quantitative science where we keep track of exact amounts of matter

• There are three ways to quantify matter that we can convert between

  • count

  • mass

  • volume

Measuring Matter

• Lets use apples as an example

  • We can count how many apples we have

    • 12 apples = 1 dozen

  • We can weigh our apples

    • 12 apples weigh ~ 2.0 kg

  • We can measure how much space our apples take up

    • 12 apples fills 0.20 bushels

Measuring Matter Sample problem 1

• If 12 apples fills 0.2 Bushels, How many bushels do we have if we have 50 apples?

  • This works just like our conversion factors!

Multiple Choice

What is the the conversion factor we want to use to convert from apples to bushels?

• 12 apples = 1 bushel

• 0.2 apples = 12 bushels

• 12 apples = 0.2 bushels

• 1 apple = 1 bushel

Measuring Matter Sample problem 1

• If 12 apples fills 0.2 Bushels, How many bushels do we have if we have 50 apples?

  • This works just like our conversion factors!

    • 12 apples = 0.2 bushels

  • We can use our relationship to convert our 50 apples into bushels

Fill in the Blanks

If 12 apples fills 0.2 Bushels, How many bushels do we have if we have 50 apples? Round to two decimal places

Measuring Matter Sample problem 2

• What is the mass of 90 apples if 1 dozen apples have a mass of 2.0 kg

  • what relationships do we know?

    • 1 dozen apples have a mass of 2.0 kg

    • How much is a dozen?

Measuring Matter Sample problem 2

• What is the mass of 90 apples if 1 dozen apples have a mass of 2.0 kg

  • what relationships do we know?

    • 1 dozen apples have a mass of 2.0 kg

    • 1 dozen apples = 12 apples

  • Step 1: Convert our apples to dozens

  • Step 2 Convert our dozens to kg

Fill in the Blanks

What is the mass of 90 apples if 1 dozen apples have a mass of 2.0 kg

Counting with moles

• In chemistry, we work with tiny things that are hard to count individually, so we group them into a unit called a mole

  • A mole is similar to a dozen, where it is a quick way of expressing the amount you have one object

• 1 mole= 6.02 × 10²³ things

  • Anything can be counted in moles, but in chemistry, we count particles, atoms, and formula units

Fill in the Blanks

How many pennies do you have if you have a mole of pennies?

Fill in the Blanks

How many dozen of donuts do you have if you have a mole of donuts ?

Why 6.02 × 10²³ ?

• 6.02 × 10²³ is called Avogadro's number

  • Named for an Italian Scientist who made many contributions to chemistry

Converting the number of Atoms to Moles Sample Problem 1

• How many moles of magnesium do you have when you have 1.25 × 10²³ atoms of magnesium?

  • Step 1: Identify your known relationship

    • 1 Mole Mg = 6.02 × 10²³ atoms

  • Step two Set up your conversion factor

Fill in the Blanks

How many moles of magnesium do you have when you have 1.25 × 10²³ atoms of magnesium Round to two decimal places?

Converting the number of Atoms to Moles Sample Problem 2

• How many moles of Bromine do you have when you have 2.17 × 10²³ particles?

  • Step 1: Identify your known relationship

    • 1 Mole Br = 6.02 × 10²³ atoms

  • Step two Set up your conversion factor

Fill in the Blanks

How many moles of Bromine do you have when you have 2.17 × 10²³ particles? Round to Two Decimal Places

Fill in the Blanks

How Many Moles is 2.80 × 10 ²⁴ atoms of silicon? Round to Two Decimal Places

Molar Mass

• When we measure things like molecules, they can contain different numbers of atoms and be of different sizes

  • NaCl has 1 Sodium and 1 Chlorine = 2 atoms total

  • H₂O has 2 hydrogen and 1 oxygen= 3 atoms total

• The mass of one mole of any atom/molecule will be dependent on how big the atom/molecule is

• Molar Mass: The mass of one mole of a substance

  • For elements, this is the same as the atomic mass, with the unit being grams/mol

Match

Match the following elements to their Rounded molar masses

• H

• O

• C

• N

• Cu

1

16

12

14

64

• 1

• 16

• 12

• 14

• 64

Multiple Choice

What is the correct unit for molar mass?

• gram

• g/mol

• liter

• mole

Fill in the Blanks

What is the molar mass of the element iron? Round to two Decimal Places

Dropdown

One ​

Select answer

is equal to 6.02 ×​ 10²³, This number is also called​

Select answer

Fill in the Blanks

If you have 2.5 moles of nitrogen, how many atoms do you have?

Molar Mass of Compounds

• Each element has its own molar mass

• When you have a compound made up of multiple elements, you simply add the molar masses for the total amounts of elements together

Molar Mass of Compounds Sample Problem 1

• What is the mass of Hydrogen Peroxide (H₂O₂) rounded to a whole number?

  • Step 1: Identify the amounts we have of each element

    • 2 hydrogen

    • 2 oxygen

  • Step 2: Identify the mass of all relevant atoms on the periodic table

    • Hydrogen = 1 g/mol

    • Oxygen= 16 g/mol

  • Step 3: Find our total mass by multiplying the number of each atom by its mass

    • (2 × 1) + (2 × 16) = 2 + 32

Fill in the Blanks

What is the mass of Hydrogen Peroxide (H₂O₂)? Round to a whole number.

Molar Mass of Compounds Sample Problem 2

• Phosphorous trichloride PCl₃ is used in the production of many herbicides and pesticides. What is the Molar Mass of (PCl₃)

  • Step 1: Identify the amounts we have of each element

Dropdown

Phosphorous Trichloride (PCl₃) has​

Select answer

phosphorous atom and ​

Select answer

chlorine atoms

Molar Mass of Compounds Sample Problem 2

• Phosphorous trichloride PCl₃ is used in the production of many herbicides and pesticides. What is the Molar Mass of (PCl₃)

  • Step 1: Identify the amounts we have of each element

    • 1 phosphorous

    • 3 Chlorine

  • Step 2: Identify the mass of all relevant atoms on the periodic table

Multiple Choice

What is the Molar mass of phosphorous rounded to a whole number?

• 31

• 15

• 17

• 35

Multiple Choice

What is the Molar mass of chlorine rounded to a whole number?

• 31

• 15

• 17

• 35

Molar Mass of Compounds Sample Problem 2

• Phosphorous trichloride PCl₃ is used in the production of many herbicides and pesticides. What is the Molar Mass of (PCl₃)?

  • Step 1: Identify the amounts we have of each element

    • 1 phosphorous

    • 3 Chlorine

  • Step 2: Identify the mass of all relevant atoms on the periodic table

    • Phosphorous = 31 g/mol

    • Chlorine= 35 g/mol

  • Step 3: Find our total mass by multiplying the number of each atom by its mass

    • (1 × 31) + (3 × 35)

Fill in the Blanks

What is the Molar Mass of (PCl₃) Round to A whole Number

Fill in the Blanks

Sodium Bicarbonate is the chemical name for Baking Soda and has the formula NaHCO₃. What is the molar mass of this chemical? Round to a whole number

Fill in the Blanks

The formula for Sucrose is C₁₂H₂₂O₁₁. What is the molar mass

Avogadro's Hypothesis

• When we look at the volume of gases, we use the unit liters as our bas unit

• All Gases have the same molar volume at STP, regardless of their size

  • 1 mole=22.4 L

Molar Conversions

• Sometimes we want to change from particles to grams or grams to liters

• When we do this, we use Moles as an intermediate step for all substances

Converting With Moles sample Problem 1

• Aluminum combines with oxygen to create aluminum oxide (Al₂O₃), which protects metal from corrosion. What is the mass in grams of 9.45 mol of aluminum oxide?

  • Step 1: Identify what we need to know

Multiple Choice

To find out the mass of 9.45 moles of Al₂O₃, what do we need to know

• the molar mass of Al₂O₃

• The liters of Al₂O₃

• The number of particles of Al₂O₃

• nothing, the moles and mass are the same thing

Converting With Moles sample Problem

• Aluminum combines with oxygen to create aluminum oxide (Al₂O₃), which protects metal from corrosion. What is the mass in grams of 9.45 mol of aluminum oxide?

  • Step 1: Identify what we need to know

    • The molar mass of Al₂O₃

  • Step 2: Calculate the molar mass of Al₂O₃

    • 2 Aluminum, 3 Oxygen

Multiple Choice

What is the rounded molar mass of Aluminum?

• 8

• 16

• 13

• 27

Multiple Choice

What is the molar mass of Oxygen

• 8

• 16

• 13

• 27

Converting With Moles sample Problem 1

• Aluminum combines with oxygen to create aluminum oxide (Al₂O₃), which protects metal from corrosion. What is the mass in grams of 9.45 mol of aluminum oxide?

  • Step 1: Identify what we need to know

    • The molar mass of Al₂O₃

  • Step 2: Calculate the molar mass of Al₂O₃

    • 2 Aluminum, 3 Oxygen

    • 1 Aluminum=27, 1 Oxygen= 16

    • (2 × 27) + (3×16)

Fill in the Blanks

What is the molar mass of Al₂O₃?

Converting With Moles sample Problem 1

• Aluminum combines with oxygen to create aluminum oxide (Al₂O₃), which protects metal from corrosion. What is the mass in grams of 9.45 mol of aluminum oxide?

  • Step 1: Identify what we need to know

    • The molar mass of Al₂O₃

  • Step 2: Calculate the molar mass of Al₂O₃

    • Al₂O₃ = 102 g/mol

  • Step 3: Convert your moles to grams

Fill in the Blanks

What is the mass in grams of 9.45 mol of aluminum oxide?

Converting With Moles Sample Problem 2

• What is the mass in grams of 2.50 mol of Oxygen Gas (O₂)

  • Step 1: Identify what you need to know

    • The Molar mass of O₂

Fill in the Blanks

What is the Molar mass of the Element Oxygen? Round to a whole Number!

Converting With Moles Sample Problem 2

• What is the mass in grams of 2.50 mol of Oxygen Gas (O₂)

  • Step 1: Identify what you need to know

    • The Molar mass of O₂

    • Oxygen has a molar mass of 16. O₂ has 2 oxygen

      • 2 × 16 =32 g/mol

  • Step 2: Use your molar mass as a conversion factor for your wanted amount

Fill in the Blanks

What is the mass in grams of 2.50 mol of Oxygen gas? Round to a whole number

Fill in the Blanks

What is the molar mass of NaCl? Round to a Whole Number

Fill in the Blanks

How many moles of sodium chloride are in a 321.8 g sample? Round to two decimal places!