Download The Mole - South Kingstown High School

The Mole
Atomic Mass
• Relative weight - the atomic mass unit
(amu) is used to describe the mass of an
atom relative to a carbon-12 isotope.
• 1mole of any element makes the relative
weight equal to the gram weight.
Element
H
O
relative weight
1 amu
16 amu
atomic weight
1 g/mol
16 g/mol
The Mole
• A mole is a quantity - 1 mole of any
substance contains 6.02 x 1023 particles
– Example:
– 1 dozen = 12 things
– 1 pair = 2 things
– 1 ream = 500 things
• Avogadros’s number = 6.02x1023
Molar Mass (MM)
• The mass in grams of 1 mole of a
molecule is the molar mass.
• The mass in grams of an ionic compound
is called the formula mass.
• A formula unit is an ionic compound.
Molar or Formula Mass
Calculations
Example:
1. What is the formula mass of CuO?
Cu = 63.55 g/mol O = 16.00 g/mol
CuO = 63.55 + 16.00 = 79.55 g/mol
2. What is the molar mass of H2O?
H = 1.01 g/mol, O = 16.00 g/mol
H2O = (1.01 x 2) + 16.00 = 18.02 g/mol
Molar Mass
• Formula mass and molar mass are
calculated the same way. Formula mass
refers to ionic compounds and molar mass
refers to molecules.
• The formula gives the mole ratio of each
atom in the compound.
Example: 1 mole of H2O = 2 mole of
hydrogen atoms and 1 mole of oxygen
atoms
Mole Conversions
• Balanced chemical equations give the
mole ratio of reactants and products.
– 2H2 + O2  2H2O : 2 moles of hydrogen
reacts with 1 mole of oxygen to make 2 moles
of water.
• To find grams or molecules/formula units
you must convert using moles.
Converting Between
Moles and grams
1. How many grams is 2 moles of water?
 Use the molar mass to convert between
moles and grams:
2 moles H2O x 18.02 g = 36.04 g
mole
2. How many moles are in 5.0 grams of
H2O?
5 g H2O x mole = .28 moles
18.02 g
Converting between
Molecules and Moles
1. How many molecules are in 2 moles of
water?
 Use Avogadro's number to convert from
moles to molecules.
2 moles H2O x 6.02 x 1023 molecules =
mole
1.20 x 1024 molecules