Experience Chemistry 05.2: Moles and Molar Relationships

• Calculating Molar Mass of Compounds

• Converting between moles and Various Units

Molar Mass of Compounds

• Recall: 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

Experience Chemistry | Lesson 5.1 & 5.2

Molar Mass of Compounds Sample Problem 1

• What is the mass of Hydrogen Peroxide (H₂O₂)?

  • 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

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2

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)

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2

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)

Experience Chemistry | Lesson 5.1 & 5.2

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

Experience Chemistry | Lesson 5.1 & 5.2