Mass Relationships
The Mole and Stoichiometry
The Mole
• A mole is the number of atoms in exactly
12 grams of 12C (carbon-12 isotope)
• One mole is equal to 6.02x1023 particles
• A particle will be an atom(elements) or
molecule(compounds)
• The number 6.02x1023 is known as
Avogadro’s number
Molar Mass
• The mass of one mole of any chemical
substance is numerically equal to the
periodic table weight of the substance
• The gram mass of one mole of substance
is known as the molar mass
• Molar mass has the unit grams per mole
(g/mol)
• Molar mass is used as a conversion factor
between gram and mole values
Molar Mass
• What is the molar mass of carbon dioxide?
– Formula: CO2
Formula mass: 44 amu
– Molar Mass: 44 g/mol
Molar Mass
• What is the molar mass of carbon dioxide?
– Formula: CO2
Formula mass: 44 amu
– Molar Mass: 44 g/mol
Conversions using molar mass
• Convert 5.0 g of CO2 to moles of CO2
– Divide 5.0 g by the molar mass
– 5.0 x 1 mole = 0.114 moles CO2
–
44 g
Conversions using molar mass
• Convert 2.0 mol of CO2 to grams of CO2
– Multiply moles by the molar mass
– 2.0 mol x 44g = 88 g CO2
–
1 mole
Conversions using Avogadro’s #
• Convert 2.0 mol of CO2 to molecules of
CO2
– Multiply moles by Avogadro’s #
– 2.0 mol x 6.02x1023 = 2.4x1024 CO2 molecules
–
1 mole
Conversions using Avogadro’s #
• Convert 2.0x1026 mol of CO2 to moles of
CO2
– Divide moles by Avogadro’s #
– 2.026 CO2 x 1 mole = 330 CO2 molecules
–
6.02x1023
Quiz Time!
Make the following computations
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What is molar mass of water?
A) 12 g/mol
B) 16 g/mol
C) 18 g/mol
D) 19 g/mol
Make the following computations
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What is the mass of 2 moles of water?
A) 24 g/mol
B) 36 g/mol
C) 18 g/mol
D) 9.0 g/mol
Make the following computations
• How many moles are in a 1.0 kg sample of
water?
• A) 56 g/mol
• B) 6.0 E23 g/mol
• C) 18 g/mol
• D) 6.0 E26 g/mol