1. Atomic mass and THE MOLE
Finding grams, moles, atomic mass, and molecules

2. THE MOLE (mol)-review What is a mole? Avogadro's Number
A mole is equal to the number of carbon atoms in exactly 12 grams of pure C12
Avogadro's Number
One mole of something contains exactly *1023 units
This is known as Avogadro’s number

3. Molar mass vs. Atomic mass
Molar mass is the total mass of the compound
Molar mass by definition is mass in grams of one mole of a substance
Atomic mass is the mass of each individual atom
Finding the molar mass
XaYb
Mass of a moles X + mass of b moles Y
Example
1. Find the molar mass of benzene C6H6
2. Find the molar mass of Calcium Carbonate

4. Converting between moles and grams
Grams moles
g *(1mole / molar mass)=mol
Examples
1. if you have 10 grams of carbon how many moles?
2. if you have 33 grams of sulfur how many moles?
3. if you weigh out 19.3 grams of copper how many moles do you have?
Moles grams
mol *(molar mas/1 mol)=g
Examples
1. if you have 6 moles of hydrogen how many grams?
2. If you have 3 moles of nitrogen how many grams?
moles of oxygen would be how many grams?

5. Finding the number of atoms (element)
Given grams
Atoms= gram*(1mol/molar mass)*(6.022*1023atoms/1 mol)
Given moles
Atoms= mol * (6.022*1023atoms/1 mol)
Given atoms
Grams= atoms *(1 mol/6.022*1023atoms)*(molar mass/1mol)
Moles= atoms *(1 mol/6.022*1023atoms)
Examples
Carbon
Nitrogen
Oxygen

6. Find the number of moles of a compound
A compound has a molar mass similar to that of an atom
The molar mass of a compound is the sum of the molar masses of the individual atoms
EX. What is the molar mass of H2O?
2 hydrogen’s so atomic mass=1.008 thus hydrogen totals 2.016g
1 oxygen =16.0
The water molecule then has a molecular mass of g

7. Finding the number of atoms (compound)
Steps
Find the molar mass
Find the moles of the molecule
Find the atoms of molecule
Find the atoms of element in the molecule
Example:
Find the number of molecules of H2CO3 in 43grams, find the number of each atom present in 43 grams

8. Molar mass  2(1.008)+1(12.01)+3(16.0)=62.03 g
Find the number of molecules of H2CO3 in 43grams, find the number of each atom present in 43 grams
Molar mass  2(1.008)+1(12.01)+3(16.0)=62.03 g
Moles 43grams H2CO3 *1mole/62.03g =0.693 moles
Atoms moles * *1023 molecules/moles= * 1023 molecules
Atoms of each element
Hydrogen => 4.17 * 1023 molecules *2 hydrogen atoms/molecule) =8.34 * 1023 atoms of hydrogen
Carbon=> 4.17 * 1023 molecules *1 carbon atoms/molecule) =4.17 * 1023 atoms of carbon
Oxygen=> 4.17 * 1023 molecules *3 oxygen atoms/molecule) =1.251 * 1024 atoms of carbon

9. Practice problems Find the molecular mass Find the number of moles
CH4
NaOH
PCl5
Find the number of moles
2.0 grams of NH3
0.9 grams of H2O
5.2 grams of KOH
Find the number of atoms
2.0 moles of C7H14O2
4.2 grams of C7H14O2
0.93 grams of CaCl2