Section 2 lesson 3: Moles and Molar mass

Section 2 lesson 3:

Moles and Molar mass

By Abby Fancsali

Multiple Choice

Which of the following equations represents a decomposition reaction?

• 2Sb + 3I₂ -> 2SbI₃

• 2 HgO -> 2 Hg + O₂

• FeS + 2HCl -> H₂S + FeCl₂

• Zn + H₂SO₄ -> ZnSO₄(aq +H₂

Multiple Choice

The reaction Pb(NO₃)₂ + 2KI -> PbI₂ + 2KNO₃ is what type of reaction?

• double-displacement reaction

• synthesis reaction.

• decomposition reaction.

• combustion reaction.

What is a Mole?

• A mole: A special unit to express amounts of small items

  • Think of a mole like a descriptor measurement (like one dozen = 12)​

    • 1 mole= 6.022 x 10²³

      • 6.022 x 10²³ is called Avogadro's number

    • Moles can be used to count anything, but We typically use moles to count the number of atoms

• We use the mole to help convert between grams and atoms​

Molar Mass and conversions

• Molar Mass: The mass in grams of one mole of an element or substance

  • Units ar grams/mole

  • The molar mass is equal to the atomic mass of a substance

    • The only thing that changes is the units

      • Atomic mass= amu

      • molar mass = g/mol

• Setting up a mole to gram conversion is the same as any other conversion

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Example problem 1

• Determine the mass in grams of a 3.50 mol sample of Copper

  • Given: 3.50 mol of copper

  • Need: molar mass of Copper

  • mass of copper sample

• Find the mass of copper on your periodic table:

  • In general​: The atomic mass is on the bottom of an elements box

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Example problem 1

Example problem 2

​What is the mass in grams of 1.00 mol Uranium

• Given information:

  • 1.00 mol Uranium

• Needed information

  • Molar mass of Uranium

  • Mass of 1.00 mol Uranium​

• Step one: Find the mass of Uranium on the Periodic Table

 

Example problem 2

Example problem 3

What about Compounds?

• The molar mass of a compound is equal to the sum of all the molar masses of the elements that make up the compound

  • Find the molar mass of water

    • For​mula for Water: H₂O

      • 2 hydrogen = 2 * 1=2

      • 1 oxygen = 1* 16= 16

      • H₂O= 2+16=18 g/mol

  • Find the molar mass of Carbon Dioxide

    • Formula for CO₂

      • 1 Carbon= 1*12

      • 2 Oxygen= 2*16

      • CO₂=48 g/mol

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