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 mol of O atoms =

1 mol of C atoms =

1 mol of Na atoms =

1 mol of Au atoms =

1.01g

16.0g

12.01g

22.99g

197.0g

Molar Mass

• Molar Mass (MM) is the mass (in grams) of one mole of a substance.

• The formula for molar mass is

( )

( )

mass mMM

mole 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 = M x n

= 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 CalculationsExample 4: How many atoms of gold are in a 232.8g of pure gold?

Step 1: Determine the number of molesn = 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 multiplyAtoms = (1atom/particle)(7.10 x1023 particles)

= 7.10 x1023 atoms

Atom CalculationsExample 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