Section 3
Moles of Compounds
Objectives:
Recognize the mole relationship shown by chemical formula
Calculate the molar mass of a compound
Calculate the number of moles of a compound from a given mass of the
compound
Determine the number of atoms or ions present in a mass of a compound
Review of Chemical Formulas
Indicates types & numbers of atoms
contained in 1 unit of compound
 Freon is CCl2F2

– 1 atom of carbon
– 2 atoms of chlorine
– 2 atoms of fluorine
Chemical Formulas
Indicate number of moles of each
element in 1 mole of the compound
 1 mol of CCl2F2 has:
–1mol C atom
–2 mol Cl atoms
–2 mol F atoms

Sample Problem

How many moles of F atoms are in 5.5
mol of freon?
5.5 mol CCl2F2 x 2 mol F atoms = 11 mol F
1 mol CCl2F2
Sample Problem 2

Determine the moles of aluminum
ions (Al 3+ ) in 1.25 moles of Al2O3.
Molar Mass of a Compound

What is it for an element?
g/mol
Determined by
adding up masses of
each element in compound
Example

Find the molar mass of potassium
chromate.
Mole To Mass Conversion


What is the mass of 2.50 moles of allyl sulfide,
(C5H5)2S?
Find molar mass of compound to use as
conversion factor
Moles x Molar Mass (g/mol) = Mass in grams
Mass to Moles Conversion


Calculate the number of moles of calcium
hydroxide in 325g.
Find molar mass of compound to use as
conversion factor
Grams x Molar Mass (mol/g) = Moles
Sample Problem

A sample of aluminum chloride (AlCl3) has a
mass of 35.6g.
– How many aluminum ions are present?
– How many chloride ions are present?
Homework

Section 11.3 Problems 15-24 on pages
876-877