Unit 5: The Mole

Molar Mass

• The sum of the atomic masses of all the atoms in the formula of a compound or molecule

Calculating Molar Mass

• Calculate the molar mass for H2O:– H = 2 x 1.0079 g = 2.0158 g– O = 1 x 15.999 g = 15.999 g

Molar mass of water = 18.0148 g

• Calculate the molar mass for Fe2(SO4)3:– Fe = 2 x 58.847 g = 117.694 g– S = 3 x 32.06 g = 96.18 g– O = 12 x 15.999 g = 191.988 g

Molar mass of iron (III) sulfate = 405.862 g

Practice Practice Practice!!!

The Mole

• A counting word, just like a dozen – A dozen = 12– A mole = 6.02 x 1023

• Two moles of marbles = 2 x 6.02 x 1023

• Three moles of hair pins = 3 x 6.02 x 1023

• 6.02 x1023 also known as Avogadro’s #– Amedeo Avogadro (Italian Scientist) aided

in this development

Mole Conversion Factor

Molar mass (g) of substance = 6.02 x 1023 molecules of substance = 1 mole of substance

Mole Conversion Factor Possibilities

• 1 molemolar mass (g)

• molar mass (g)1 mole

• 1 mole6.02 x 1023 atoms or molecules

• 6.02 x 1023 atoms or molecules1 mole

Mole Conversion Factor Possibilities

• molar mass (g)6.02 x 1023 atoms or molecules

• 6.02 x 1023 atoms or moleculesmolar mass (g)

Use the word atoms when describing a single element; use the word molecule when describing molecules and compounds

Mole Conversion Examples

Molar mass = Avogadro’s # = 1 mole18.0148 g of H2O = 6.02 x 1023 molecules of H2O = 1 mole of H2O

405.862 g of Fe2(SO4)3 = 6.02 x 1023 of Fe2(SO4)3 = 1 mole of Fe2(SO4)3

6.941 g of Li = 6.023 x 1023 atoms of Li = 1 mole of Li

Mole Conversion Practice Problem 1

• If 5,000,000 chlorine atoms are used to disinfect water, how many moles is that?

5,000,000 atoms Cl x 1 mole Cl = 8.3 x 1023 mole Cl

6.02 x 1023 atoms Cl

8.3 x 1023 mole Cl 8 x 1023 mole Cl

Correct Sig Fig

Mole Conversion Practice Problem 2

• Thirty moles of carbon monoxide could be a lethal amount. How many grams is that?

30 moles CO x 28.01 g of CO = 840.3 g of CO

1 mole CO

840.3 g CO 800 g CO

Correct Sig Fig

Mole Conversion Practice Problem 3

• One liter of water weighs 1,000 g. How many water molecules is that?

1,000 g H2O x 1 mole H2O x 6.02 x 1023 molecules H2O = 3.3 x 1023 molecules H2O

18.0148 g H2O 1 mole H2O

3.3 x 1023 molecules H2O 3 x 1023 molecules H2O

Correct Sig Fig

Practice Practice Practice!!!