1. Ch. 10.2 Mole-Mass and Mole-Volume Relationship

2. The Mole-Mass Relationship
Molar mass of any substance is the mass in grams of one mole of that substance.
Applies to atoms, molecules, formula units, etc.
With gases, you must be clear as to whether the gas is atomic or molecular ( O vs. O2).
Use the molar mass of a substance to convert between the mass of a substance and the moles of a substance (molar mass = one mole).

3. mass(grams) = # of moles x mass(grams)/moles
Ex: molar mass of NaCl is 58.5 g/moles. What is the mass of 3.00 moles of NaCl?
3.00 mol x 58.5g/mol = 176 grams

4. Practice—moles to mass
What is mass of 9.45 moles of aluminum oxide?
What is the mass of 4.52x10-3 moles C20H42?
What is the mass of 2.50 moles of iron(II) hydroxide?

5. Practice—mass to moles
Moles = mass(grams) x 1 mole/mass(grams)
How many moles in 92.2 grams of iron(III) oxide?
How many moles in 3.70x10-1g of boron?
How many moles in 75.0g of dinitrogen trioxide?

6. The mole-volume relationship
One mole of any gas, at standard temperature and pressure, will always occupy the same volume.
Reason is that, in a gas, the atoms or molecules are so far apart, that the size of the individual atoms or molecules is insignificant compared to the distances between the atoms or molecules.

7. Standard Temperature Pressure STP
Temperature: 0oCelcius
Pressure: 1 atmosphere (atm) or kilo Pascal (kPa)
One mole of any gas (6.02 x 1023 RP) at standard temperature and pressure (STP) will always occupy 22.4 liters.

8. Practice How much volume does 0.5 moles of oxygen take up?
Multiply: 0.5 moles x 22.4 l/mole =
11.2 l
How many moles N2 are found in l of gas?
Calculate: l x 1 mole / 22.4 l =
2.2 moles

9. Go To Mole Island!!! Volume of Gas
multiply moles by divide volume l/moles by 22.4 l/mole
Divide mass by Mole multiply mole with
Molar mass x 1023
multiply moles
with molar mass divide RPs Representative
Mass x Particles RP

10. Practice Problem 1 Find the number of molecules in 50.8 liters of O2
First write pathway
Volume → moles → RP
50.8 l x 1 mole/22.4l = 2.27 moles
2.27 moles x 6.02 x 1023 RP/mole= 1.36 x 1024 O2
How many atoms?
2 atoms/RP x 1.36 x 1024 RP = 2.42 x 1024 Atoms Oxygen

11. Practice Problem 2 Find the volume of 500 g of PO2
Mass → moles → volume
Molar mass of PO2
(2x16.00) = g/mol
moles: 500g x 1 mole/62.97g = 7.94 moles
Volume: 22.4moles/liter x 7.94 moles= liters

12. Practice Problem 3 How many atoms are in 400 g of C2(OH2)4
Mass → moles → RP → Atoms
Molar mass: 2x x ( x 1.01)
=96.10 g/mol
# of atoms: 14
400 g x 1 mole/96.10 g = 4.16 moles
4.16 moles x 6.02 x 1023 RP= x 1023 = 2.50 x 1024 RP
2.50 x 1024 RP x 14 atoms/RP= x 1024 =3.50 x 1025 atoms