The Mole
Mole Calculations
Molar Mass
• mass of one mole of a substance
• units: grams/mole
• equal to the ATOMIC MASS of the element,
rounded to two numbers after the decimal
point
• for compounds, equal to the SUM of the
masses of all the elements in the compound
(multiply each elements’ atomic mass by the
subscript)
Molar Mass
• What is the molar mass of Aluminum (Al)?
– Look at the PT the atomic mass for Al is 26.9815385
Round this to two digits after the decimal 26.98
– The unit for molar mass is g/mol
Al = 26.98 g/mol
• What is the molar mass of NaCl?
– Look up the mass of every element in the compound
and add them together. Round the masses before you
add!
Na = 22.99 g/mol
Cl = 35.45 g/mol
• What is the molar mass of H2O
– Find the masses of each element (round)
H = 1.01 g/mol
O = 16.00 g/mol
– Since there are 2 Hydrogen atoms multiply the
mass of Hydrogen by 2.
1.01 x 2 = 2.02
– Add that mass to the Oxygen to get your total
2.02 + 16.00 = 18.02 g/mol
• What is the molar mass of Ca (NO3)2 ?
– Subscripts outside a parenthesis will distribute to
all elements inside the parenthesis. It will not
multiply elements outside the parenthesis
N2 O6 Ca2
– Multiple the subscripts by the masses on the PT
14.01 x 2 = 28.02
16.00 x 6 = 96.00
40.01 x 1 = 40.01
164.03 g/mol
Molar Mass Cont…
1 mole of X = atomic mass of X (grams)
1 mole of X = 22.4 L of X (only if a gas at STP)
1 mole X = 6.022 x 1023 particles of X
(atoms, molecules, or ions)
NEVER put 6.022 x 1023 in front of the unit GRAMS
Particles
Atoms, molecules,
ions
1 mole = 6.022 x 1023 particles
1 mole = _____ grams
Molar Mass
1 mole = 22.4 Liters
Mass
Volume
grams or Kg
Liters
of a gas at STP
How many moles are in
11.9 grams Au?
1. Look at the Mole Chart and determine what
conversion factor to use.
2. Find the molar mass off the periodic table if you
have a mass (We do)
3. Make a railroad
4. Put the Given in the upper left
5. Add the Conversion Factor ( ___ grams = 1 mole)
6. Do the Math. Round to proper sig digs and add
the unit
• The problem talks about Mass. Look at the mole
chart …
Mass
(g or Kg)
• 1 mole = _____ grams. Use the periodic table to
find the mass of Au. (196.96 g/mol)
11.9 grams of Au
1 mole of Au
= 0.0604
196.96 grams of Au
• Add given and conversion factor to solve.
ANSWER: 0.0604183  6.04 x 10-2 moles of Au
Example #2 . . .
What is the mass of 3.60 moles of Cu?
1. Find the molar mass of the substance. (63.55 g/mol)
2. Make a railroad.
1. Add the GIVEN
1. Plug in the conversion factor
2. Do the Math
3.60 moles Cu
63.55 grams of Cu
1 mole of Cu
Answer: 228.78 grams round to proper sig digs
229 grams of Cu
How many molecules are in 2.5 moles
of H2O ?
• The problem talks about Molecules. Look at the
mole chart …
Particles
(atom, molecule)
• 1 mole = 6.022 x 1023 particles
2.5 moles H2O
6.022 x 1023 particles H20
1 mole of H2O
Molecules are a type of particle so they are interchangeable
ANSWER: 1.5055 x 1024
1.5 x 1024 molecules H2O
How many moles are in 10.0 Liters of
CO2 gas at STP?
• The problem talks about Liters. Look at the mole
chart …
Volume
(mL or L)
• 1 mole = 22.4 Liters
10.0 Liters of CO2
1 mole of CO2
22.4 Liters of CO2
ANSWER: 0.446428 
0.446 Liters of CO2