STUDY GROUPS- MEET NEXT WEEK

1
Announcements

• STUDY GROUPS- MEET NEXT WEEK
• HEADS-UP EXAM 1 FRIDAY, SEPTEMBER 18TH

2
How many C atoms are in a 0.96-carat diamond
ring? (1 carat 0.2g)

1. 9.63 x 1021
2. 1.38 x 1024
3. 4.81 x 1022
4. 3.47 x 1025

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Compounds and Moles

• 1 mole of a compound contains 6.022 x 1023
  molecules or units
• Molar mass sum of atomic molar masses
• H2O
• CO2
• Fe(NO3)3

4
Examples to try(answers posted on web site under
lecture notes)

• Consider UF6
• What is the molar mass?
• How many grams in 0.5 mol?
• How many molecules in 0.5 mol?
• How many U atoms in 0.5 mol of UF6?
• How many F atoms in 0.5 mol UF6?

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Molecular vs. Nonmolecular compound terms

• 1 mol CO2 contains 6.022 x 1023 molecules
• 1 mol NaCl contains 6.022 x 1023 formula units

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Percent Composition

• The fraction of mass due to an element

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Determining Formulas from Composition

• The ratio of atoms in the formula is the same as
  the ratio of moles of those elements.
• If you determine the ratio of moles, you know the
  formula.
• However, the formula determined is the empirical
  formula.

8
Which of the following has the highest
composition of copper, Cu? (dont calculate)

1. CuSO4
2. Cu2SO4
3. CuCO3
4. Cu2CO3

9
Examples

• 8.65g of iron combines with 3.72g of oxygen. What
  is the empirical formula of this compound?
• Formaldehyde contains 40.0 C, 6.7 H, and 53.3
  O. What is the empirical formula?

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Empirical vs. Molecular Formulas

• Formaldehyde
• Empirical CH2O
• Molar mass of empirical formula 30.03g/mol
• Actual Molar mass 30.03g/mol
• Molecular CH2O

• Fructose
• Empirical CH2O
• Molar mass of empirical formula 30.03g/mol
• Actual Molar mass 180.16g/mol
• Divide actual molar mass by empirical formula
  mass to get multiplier
• 180.16/30.036
• Molecular C6H12O6

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Example

• A hydrocarbon has 82.65C and 17.34H. The molar
  mass is 58.12 g/mol. What are the empirical and
  molecular formulas?