Calculating Moles and Number of Atoms

1
Calculating Moles and Number of Atoms

• Use Periodic table of Elements to find Molar
  Mass.
• If the mass of the substance is known, set up
  proportion to find the amounts of X moles.
• When you know the amount of moles
• 1 mol 6.022 x 1023
  particles/atoms/units/molecules
• Set up proportion to find the amount of
  particles/atoms/units/molecules

2
Examples

• How many moles in 34.2 g of sulfur?
• 1.06 mol Sulfur
• How many grams in 1.20 moles of carbon?
• 14.4 g Carbon

3
More Examples

• How many atoms in 3.91 moles of sodium?
• 2.35 x 1024 atoms
• What mass would 4.52 x 1024 molecules of water
  have?
• 135 g H2O

4
Molar Mass of Compounds

• Sum of individual elements mass.
• The Molar Mass of a compound 1 mole of the
  compound.
• Examples
• Find the amount of moles in 30 grams of
  H3PO4 0.31mol

5
Examples

• 1.1 grams of FeCL3, how many moles is this?
• 6.8 x 10-3 mol
• What is the mass of 4 moles of Cu(CN)2?
• 462 g

6
More Examples

• What is the mass of 3.5 x 10-4 moles of H2O?
• 6.3 x 10-3 g

7
Percent Composition of Compounds

• Find the Molar Mass of the Compound.
• The mass of each element in the compound is
• The mass of the element in 1 mole of the compound
  divided by the Molar Mass of the compound. Then
  multiply by 100.

8
Examples

• Determine the mass percent of each element of
  each element in H2SO4 (what is the name of this
  compound?).
• H gt 2.1
• S gt 32.7
• O gt 65.2

9
More Examples

• Determine the mass percent of each element in
  isopropyl alcohol, C3H7OH.
• C gt 60
• H gt 13
• O gt 27

10
Determining Empirical Formulas

• A 1.500 g sample containing only carbon and
  hydrogen is found to contain 1.198 g of carbon.
  What is the empirical formula?
• CH3

11
More Examples

• A compound has the following mass composition
  66.75 copper, 10.84 phosphorus, and 22.41
  oxygen. Find the empirical formula for this
  compound.
• Cu3PO4