Transcript Molar Mass Calculations

Quantities in Chemistry
The Relationship Between
Mole and Molar Mass
Mole Review
• A Mole is a unit of measurement in chemistry. It
represents 6.02 x 1023 of an entity. One mole of sodium is
6.02 x 1023 atoms of sodium.
• The symbol for mole is “n”.
The unit for mole is “mol”
• 6.02 x 1023 is also known as Avogadro’s number.
How do we measure out 1 mol?
• Do you count out 6.02 x 1023 atoms in the
lab?
• Do you use special equipment?
• Can you measure it as a volume?
• Can you measure it as a mass?
Amazing!
1 mole = amu of the element in grams
For Example:
1 mol of H atoms = 1.01g
1 mol of O atoms = 16.0g
1 mol of C atoms = 12.01g
1 mol of Na atoms = 22.99g
1 mol of Au atoms =197.0g
Molar Mass
• Molar Mass (MM) is the mass (in grams)
of one mole of a substance.
• The formula for molar mass is
MM 
m ass ( m )
m ole ( n )
• For example, Hydrogen’s molar mass = 1.01 g/mol
Molar Mass of Compounds
• The molar mass of a compound is equal to
the sum of the molar masses of the atoms in
the molecules or ions in the compound.
• For example, the molar mass of water is:
• MH2O= 2(MH) + (MO)
= 2(1.01g/mol) + 1(16.0g/mol)
=18.02 g/mol
Example: Find the molar mass of
H2CO2
• M H2CO2 = 2(MH) + (MC) +2(MO)
= 2(1.01g/mol) + (12.00g/mol) + 2(16.0g/mol)
=46.02 g/mol
Atoms, Moles, Mass & Molar
Mass Calculations
• Example 1: Calculate the molar mass of
magnesium if 0.330 mol has a mass of 8.02 g
M=m/n
= 8.02g/0.330mol
= 24.3g/mol
Atoms, Moles, Mass & Molar
Mass Calculations
• Example 2: Calculate the mass, in grams, of
2.00 mol of calcium atoms.
M=m/n
m=Mxn
= 40.08g/mol x 2.0 mol
= 80.2g
Atoms, Moles, Mass & Molar
Mass Calculations
• Example 3: How many moles of gold are in
275.8g of pure gold?
M=m/n
n = m/M
= 275.8g / 197.0 g/mol
= 1.400 mol
Calculating Number of Atoms
• If you have a mass of the number of moles of an
item, you can determine the number of
molecules in an amount of an element using
Avogadro’s number.
• Avogadro’s number = 6.02 x 1023 particles/mol
Atom Calculations
Example 4: How many atoms of gold are in a 232.8g of pure gold?
Step 1: Determine the number of moles
n = m/M
= 232.8g / 197.0g/mol
= 1.182 mol
Step 2: Using Avogadro’s number and the number of moles,
determine the number of particles.
N= n x NA
= 1.182 mol x 6.02 x 1023 particles/mol
= 7.12 x 1023 particles
Step 3: Determine the number of atoms per particle, and multiply
Atoms = (1atom/particle)(7.10 x1023 particles)
= 7.10 x1023 atoms
Atom Calculations
Example 5: How many atoms of oxygen are in a 230.0g of oxygen
gas?
Step 1: Determine the number of moles
n = m/M
= 230.0g / 32.0g/mol
= 7.188 mol
Step 2: Using Avogadro’s number and the number of moles,
determine the number of atoms.
N= n x NA
= 7.188mol x 6.02 x 1023 atoms/mol
= 4.327 x 1024 atoms
Step 3: Determine the number of atoms per particle, and
multiply
Atoms = (2 oxygens)(4.327x1024atoms)
= 8.654 x1024 atoms of oxygen