Unit 6: Stoichiometry

Section 2: Moles, Masses, and Molecules, OH MY!!!!!

The Mole

• A counting unit, 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 Koa trees= 3 x 6.02 x 1023

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

aided in this development

Molar Mass

• The sum of the atomic masses of all the atoms in a formula; equals the mass of one mole of the substance.

Calculating Molar Mass

• Calculate the molar mass of H2O:– H = 2 x 1.008 g = 2.016 g– O = 1 x 16.00 g = 16.00 g

Molar mass of water = 18.016 g

• Calculate the molar mass for Fe2(SO4)3:– Fe = 2 x 55.85 g = 111.7 g– S = 3 x 32.07 g = 96.21 g– O = 12 x 16.00 g = 192.00 g

Molar mass of Iron (III) sulfate = 399.91 g

Mole Conversion Factor

1 mole of a substance

= Molar mass of a substance

= 6.02 x 1023 molecules of a 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)

The word atoms = single element; The word molecules = multiple atoms in a formula.

Mole Conversion Examples

Molar mass = Avogadro’s # = 1 mole18.016 g of H2O = 6.02 x 1023 molecules of H2O = 1 mole of H2O

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

6.941 g of Li = 6.02 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 10-18 mole Cl

6.02 x 1023 atoms Cl

8.3 x 10-18 mole Cl 8 x 10-18 mole Cl

Correct Sig Fig = the same as the given number in the problem with the lowest number of sig figs (i.e. “5,000,000”)

Mole Conversion Practice Problem 2

• Thirty (30) 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 has a mass of 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 1025 molecules H2O

18.016 g H2O 1 mole H2O

3.3 x 1025 molecules H2O 3 x 1025 molecules H2O

Correct Sig Fig

Analysis Question

Statement: 25.42g of FeCl3 is exactly 6.02x1023 molecules of

Iron (III) chloride.In 2-3 complete sentences:

Develop a claim that supports or denies this statement. Cite at least 2

pieces of evidence (conversion factors) that support your claim.