The Mole

1
The Mole

• (no, its not an animal!)

2
The Mole

• It is a quantity, like a dozen, a trio, a pair
• It is used to measure a quantity of very small
  objects, i.e., atoms and molecules
• It is 6.02 x 1023, also known as Avogadros
  number
• Not useful for measuring everyday items

3
How Much is a Mole?

• 6.02 X 1023 Watermelon Seeds Would be found
  inside a melon slightly larger than the moon.
• 6.02 X 1023 Donut Holes Would cover the earth
  and be 5 miles (8 km) deep.
• 6.02 X 1023  Pennies Would make at least 7
  stacks that would reach the moon.
• 6.02 X 1023  Grains of Sand Would be more than
  all of the sand on Miami Beach.
• 6.02 X 1023  Blood Cells Would be more than the
  total number of blood cells found in every human
  on earth.
• 6.02 X 1023  C02 Molecules Would be found in 1
  Mole BalloonTM at STP.

4
Why did scientists need a mole?

• They knew that equal volumes of gases at standard
  temp and pressure (STP) had an equal number of
  particles
• They knew that 32 g of O2 and 2 g of H2 had a
  volume of 22.4 L.
• They determined that that number of particles was
  6.02 x 1023, or one mole

5
What is the difference between atomic mass and
formula mass?

• Atomic mass is expressed in atomic mass units
• Atomic mass unit (amu) one twelfth the mass of
  the carbon 12-isotope
• Most elements do not have whole number mass
• the atomic mass is an average of the masses of
  all of the isotopes of that element
• the actual mass of a proton and neutron is not
  equal to exactly 1 amu
• Formula mass the sum of the atomic masses of
  all of the atoms in a compound in amus

6
How do I calculate formula mass?

• It is found by summing the atomic masses of all
  of the atoms in a compound
• The mass unit is amus
• Example H2SO4 has 2 Hs, 1 S, and 4 Os
• 2 (1.01 amu) (32.07 amu) 4(16.00 amu)
  98.09 amu
• So, the formula mass of H2SO4 is 98.09 amu

7
What is molar mass?

• Mass of 1 mole of a compound
• Measured in grams
• It is the mass in grams of one mole of a given
  substance
• It is equal to the average atomic mass of that
  element, written in grams
• It depends on the masses of the elements that
  make up the substance
• It is calculated exactly like formula mass, but
  with different units (g instead of amu)

8
How to find molar mass

• Find the molar mass of Na2SO4
• Find the molar mass of MgSO4 7H2O

9
How do I convert from moles to mass?

• You must use molar mass
• How many moles of water are in 18.01 g of water?
• What is the mass of 15.2 moles of CO2?

10
What is Avogadros Number?

• 6.02 x 1023 the number of representative
  particles (atoms, molecules, formula units) in
  exactly one mole of a substance
• Atoms The representative particle in an element
• Molecules The representative particle in a
  molecule of liquid
• Formula Units The representative particle in a
  compound
• Mole the fundamental SI unit used to measure
  the amount of a substance

11
How can I convert moles to number of particles?

• Avogadros Number is used as a factor in
  converting from a given number of moles to the
  equivalent number of atoms.
• To convert from moles to number of particles, you
  must use dimensional analysis.

12
How do I convert moles to particles?

• Remember Avogadros Number
• 6.02 x 1023 particles
• 1 mole
• So, moles x 6.02 x 1023 particles
• 1 mole
• particles

13
Sample Problems

• A) atoms in 2.50 mol Zn
• B) molecules in 11.5 mol H2O

14
How do I convert moles to volume?

• Molar volume the volume of 1 mole of a gas at
  standard temperature and pressure (0C and 1
  atmosphere abbreviated STP)
• Gases change volume with changes in temperature,
  pressure, or both so, temp and press must be
  specified when giving the volume of a gas
• 1 mole of gas 22.4 L
• This is true ONLY at STP

15
To convert moles to volume

• How many moles will be in 44.8 L of O2?
• What is the volume of 0.725 moles of NH3?

16
How do I combine multiple conversions?

• You can combine the above processes together to
  simplify calculations