1. The Mole Concept

2. AMU, grams, mol
We used atomic mass units to determine the mass of atoms because they are so tiny
We use grams in the laboratory because it is a larger measurement and is more convenient
We will use moles (mol) to count the number of atoms in samples with masses given in grams

3. Consider this...
What mass of copper contains the same number of atoms as 26.98g of aluminum?
Look at the atomic masses of each element.
Al = amu
Cu = amu
*This is based on 1 atom
So…
26.98g Al = 63.55g Cu (same number of atoms)
26.98 g Al has the same number of atoms as g of copper.
The ratio of atomic masses is equal the the ratio of sample masses.

4. 26.98 g Al has the same number of atoms as 63.55 g of copper.
A sample of an element with a mass equal to that element’s average atomic mass expressed in grams contains 1 mol of atoms.

5. Consider this...
If we have g silver, how many grams of lead would be needed to have the same number of atoms?
Ag = amu
Pb = amu
Therefore…
107.87g Ag = 207.2g Pb (same number of atoms)
Now, how many atoms are actually in each of these gram samples?

6. Moles -We use moles (mol) to determine the number of atoms in samples
- Defined as: the number equal to the number of carbon atoms in g of C
- Application: any element that weighs a number of grams equal to the average atomic mass of that element contains x 1023 atoms (1mol) of that element.
- This is called Avogardo’s number.
Ex: 1 dozen of eggs is 12 eggs
Ex: 1 mole of water has x 1023 atoms of H2O molecules

7. Mole

9. Using the Mole in Calculations
Avogadro’s number is defined such that a sample of any element that weighs a number of grams equal to the average atomic mass of that element contains
6.022 x 1023 atoms (1 mol) of that element.
Element
Mass of Sample (g)
Number of Atoms Present
Gold
196.97
6.022 x 1023
Iron
55.85
Boron
10.81

10. Try this...
A sample of H contains 1 mol of H atoms and has a mass of 1.01 g. A second sample of H has a mass of g. How many atoms are present in the second sample?
1 mol H atoms = 1.01 g H
0.500 g H x 1 mol H = mol H in second sample
g H
Now, how many atoms is this?
Remember 1 mol = x 1023
0.495 mol H atoms x x 1023 H atoms = 2.98 x 1023
mol H atoms

11. Try this...
Find both the number of moles of atoms and the number of atoms in a 10.0g sample of aluminum.

12. Try this...
Find both the number of moles of atoms and the number of atoms in a 10.0g sample of aluminum.
10.0g Al x 1 mol Al = mol Al
26.98 g Al
0.371 mol Al x x 1023 Al atoms = x Al atoms
1 mol Al
Does this make sense? Since 10 g is smaller than 26.98g, we should have fewer than x Al atoms. So yes, it makes sense.

13. Molar Mass
The molar mass of any substance is the mass (in grams) of 1 mol of the substance.
The molar mass is obtained by summing the masses of the component atoms.

14. Try this... Find the mass of mol of CH4 (methane).
1 mol of C = 1 x g = g
4 mol of H = 4 x g = g
Mass of 1 mol of CH4 = g
When adding/subtracting, go to the least number of decimal spaces.

15. Try this...
Calculate the molar mass of 1 mol SO2 (sulfur dioxide).

16. Try this... Calculate the molar mass of 1 mol SO2 (sulfur dioxide).
Mass of 1 mol of S = 1 x = g
Mass of 2 mol of O =2 x = g
Mass of 1 mol of SO2 = g = molar mass = g/mol

17. Try this...
Calculate the molar mass of 1 mol of table salt NaCl.

18. Try this... Calculate the molar mass of 1 mol of table salt NaCl.
Na = g
Cl = g
54.44 g/mol NaCl

19. The molar mass of a substance can be obtained by summing the masses of the component atoms.
The molar mass in grams represents the mass of 1 mol of a substance.
Once we know the molar mass of a compound we can compare the number of moles present in the sample of known mass.

20. Calculate Mass from Moles
Calculate the molar mass of calcium carbonate CaCO3 (calcite).
Ca = g/mol
C = g/mol
O = g/mol (x3)
100.0 g/mol CaCO3
If we have 4.86 mol of CaCO3, how many grams would that be?
4.86 mol CaCO3 x g/CaCO3 = 486 g CaCO3
mol CaCO3

21. Grams can also be calculated from the moles in a sample.
Calculate the molar mass of C10H6O3.
C = g/mol (x10 mol) g
H = g/mol (x6 mol) g
O= g/mol (x3 mol) g
174.1 g/mol C10H6O3
How many moles are in 1.56 g of C10H6O3 ?
1.56 g C10H6O3 x 1 mol C10H6O3 = mol C10H6O3 = 8.96 x 10-3 mol C10H6O3
174.1 g C10H6O3
1 decimal place; use least number of decimal places.