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
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