Unit 3 Lesson More Moles

Unit 3 Lesson

More Moles!

Remembering the Mole

• mole – The amount of a substance that contains the same number of particles as the number of atoms in 12 g of carbon-12.

• The mole is a counting unit, like a dozen.

Avogadro's Number

• Avogadro’s # = 6.022 x 10²³

• 1 mole of carbon-12 = 6.022 x 1023 atoms of carbon-12 = 12 g of carbon-12

Molar Mass

• The mass (in grams) of one mole of an element.

• So the molar

  mass of carbon-12 is 12 g.

• (If it were a compound, instead of just an element, you simply add

  up the masses of all the atoms in the formula.)

Time for some practice problems

-->

Open Ended

What is the Molar mass of NaCl?

Open Ended

Convert 5.38 g of Al₂O₃ into moles of Al₂O₃

Open Ended

Convert 2.02 moles of Lithium fluoride into grams of Lithium fluoride

Open Ended

Convert 4.01x10²⁴ formula units of Magnesium Chloride to moles of Magnesium Chloride

Open Ended

Convert 4.81 g of Fe(NO₃)₂ into formula units of Fe(NO₃)₂

New material coming up

-->

Molar Mass of Compounds

• To find the molar mass of a compound, simply add up the masses of all the atoms in the formula, and give the total mass (in grams).

• For example, the molar mass of H2O = 18.0 g.

Percent Composition By Mass

• To find the percentage composition of an element in a compound, first find the molar mass of the compound.

• Then divide the element mass by the compound mass.

• (Think of it this

  way: What percentage of the total mass of the compound comes from that specific element?)

At the top is the formula for percent composition