1. Chemical Measurements
Unit 1: Stoichiometry
Chapter 10 – The Mole

2. Monday, 2/2 Learning Target:
Distinguish between atomic mass, formula mass and molar mass.
Learning Outcome:
Complete “Formula Mass and Molar Mass” Worksheet.

3. Measurements in Chemistry
We use measurements all of the time!
Atomic Mass is a measurement that we have already used in class.
units for atomic mass = atomic mass unit (amu)
Used to express masses of atoms on a relative scale. We compare everything to carbon-12.

4. Particle
location
Mass (amu)
Mass (g)
Proton
Inside nucleus
1.673X10 -24
1.0073=1
Neutron
Inside nucleus
1.675X10 -24
1.0087=1
Electron
Outside nucleus
7.109X10 -28
0.0006=0

5. Atomic Mass & Formula Mass
The weighted average of the masses of the existing isotopes of an element
Ex. Carbon C amu
Formula Mass
The sum of the atomic masses of all atoms in a compound
Ex. Carbon Dioxide CO amu

6. Calculating Formula Mass
What is the formula mass for SO2?
S: 1 atom x 32.1 amu
O: 2 atoms x 16.0 amu
Formula Mass = 32.1 amu amu= 64.1 amu

7. Calculating Formula Mass
What is the formula mass for H2O2?
H: 2 atoms x 1.01 amu
O: 2 atoms x 16.0 amu
Formula Mass = 2.02 amu amu = amu

8. Calculating Formula Mass
Methylene chloride (CH2Cl2) is used as a solvent in paint strippers. What is the formula mass of methylene chloride?
C: 1 atom x amu
H: 2 atoms x 1.01 amu
Cl: 2 atoms x amu
Formula Mass = 12.01(1) (2) (2) = 85.0 amu

9. Moving from AMU to grams
The use of atomic mass units (amu) are impractical in the chemistry lab where the preferred unit of measurement is grams.
Scientists needed to establish a relationship between # of atoms and masses of atoms.

10. The Mole
Definition
The number of atoms of that element equal to the number of atoms in exactly 12.0 grams of carbon-12.
Abbreviated mol (without the ‘e’)
The number of atoms in one mole of atoms is always the same! Avogadro’s Number (N)
6.02 x 1023 atoms
602,000,000,000,000,000,000,000

11. Same Number, Different Mass
Element # atoms/mol mass of 1 mole
Carbon 6.02x1023 atoms
12.01 g C
Copper 6.02x1023 atoms
63.55 g Cu
Tin 6.02x1023 atoms
g Sn
Why do the amounts of each look different?

12. Calculating Molar Mass
Methylene chloride (CH2Cl2)
C: 1 atom x amu
H: 2 atoms x 1.01 amu
Cl: 2 atoms x amu
Formula Mass = 12.0(1) + 1.0(2) (2) = 85.0 amu
Molar Mass = g/mol

13. Molecules and Moles
The number of molecules in 1mole of a molecular compound is 6.02 x 1023 (same as with atoms in a mole)
1 mol of water (H2O) contains 1 mol of water molecules but 2 mol of hydrogen atoms and 1 mol oxygen.
How many moles of Ca2+ and F- are in 1 mole of calcium fluoride?
1 mole of Ca2+ ions and 2 moles of F- ions

14. Molar Mass
Definition
The mass in grams of 1 mole of a substance
We calculate molar mass the same way as formula mass.
Atomic/Formula Molar Mass
Ex. Calcium amu = g/mol

15. Same Number, Different Mass Practice
What is the formula and molar mass for propane, C3H8?
C: 3 atoms x amu = amu
H: 8 atoms x 1.01 amu = 8.08 amu
Formula Mass = amu amu = amu
Molar Mass = g/mol

16. Same Number, Different Mass Practice
What is the formula and molar mass for glucose, C6H12O6?
C: 6 atoms x amu = amu
H: 12 atoms x 1.01 amu = amu
O: 6 atoms x amu = amu
Formula Mass = amu amu + 96 amu = amu
Molar Mass = g/mol