1. Mole Calculations Lesson 3

2. Avogadro’s number

3. Review
The mole is the fundamental unit in chemistry for measuring the AMOUNT OF SUBSTANCE. We can convert from moles to number of particles.
1 mole = 6.02 x 1023  particles or molecules or atoms!
CONVERSION FACTOR
1 mol OR x 1023
6.02 x mol
This is Avogadro's number
There are no set units for Avogadro’s number because it is simply a number. You can use any of the units(particles, molecules or atoms) depending on the question.

4. Molar mass from Periodic Table
Molar Mass Units # grams or 1 mole 1 mole # grams

5. The molar mass is a new conversion factor that can convert between grams and moles.
Avogadro’s number is another conversion factor that can convert between moles and particles
Particles
Moles
Grams
1.00 mole =
6.02 x 1023 particles
Molar Mass
From Periodic Table
g / mole

6. Try
Ex: How many moles of NaBr are there in 1.7 x 1025 molecules of NaBr? Ex: How many molecules of LiCl are there in 0.5 moles of LiCl?

7. Try
Ex: how many grams are in 3 moles of Al2S3

8. STP Recall Avogadro’s hypothesis:
Equal volumes of different gases contain the same number of particles (at the same temperature and pressure).
Standard Temperature and Pressure
 Chemists have a set STANDARD for temperature and pressure:
STP = standard temperature and pressure
STP = 0 ºC and kPa

9. Molar Volume
Just like we have a molar mass, we also have a molar volume.
 The molar volume of a gas is the VOLUME occupied by ONE MOLE of the gas.
It is a fact that at STP, 1 mol of any gas occupies 22.4 L of volume
this is known as ‘molar volume’
We then get another CONVERSION FACTOR
1 mol OR L
22.4 L 1 mol
BUT ONLY AT STP, and only for gases!

10. The Molar Volume Ex: How many L will 2.3 mol of He (g) occupy at STP?
Ex: How many mol of Ne (g) will fill a 400L container at STP?

11. Find # of atoms in a molecule
 How many atoms are there in 1 molecule of CuSO4 · 5H2O?
 How many atoms are there in 15 molecules of CuSO4 · 5H2O?
Always find the # of atoms in 1 molecule first, then multiply by # of molecules (15)
How many H atoms are in CuSO4 · 5H2O?

12. CONVERSION
CONVERSION FACTOR
Moles ↔ # of Particles
(Avogadro’s number)
Moles ↔ Mass
(Molar mass)
Moles ↔ Volume
STP)
(Molar Volume)
Molecules ↔ Atoms
The MOLE is CENTRAL to all conversions between mass, volume and particles.

13. MULTIPLE CONVERSIONS
Ex: Find the mass, (in grams), of 1.25L of NH3 (g) at STP:
Ex: What is the volume occupied by 45.0g of KOH(g) at STP?

14. MULTIPLE CONVERSIONS
Ex: What is the mass of 175 N (Nitrogen) atoms?

15. MULTIPLE CONVERSIONS
What if you want to find the volume of a solid or a liquid????
Use densityd = m/V
If the volume of a liquid or solid is unknown....use V = m/d (you can always find the mass from the moles of substance present)
 This is because….you cannot use 22.4L when calculating a volume of liquid or solid (only gases!)

16. MULTIPLE CONVERSIONS
Ex: What is the volume occupied by 5.00 mol of ethanol, CH3 CH2 OH(l)?
(the density of ethanol is g/mL)
291mL

17. MULTIPLE CONVERSIONS If the number of moles is unknown...
use the density and volume to calculate mass
m = d x V and
then convert mass to moles

18. MULTIPLE CONVERSIONS
Ex: How many moles of Hg (l) are contained in 56 mL of Hg(l)? (d = 13.6 g/mL)

19. MULTIPLE CONVERSIONS
Ex: CCl4 (l) has a density of 1.59 g/mL. How many atoms of C are in 200 mL of CCl4?

20. MULTIPLE CONVERSIONS
Ex: What is the density of CH2F2 (g) at STP?

21. MULTIPLE CONVERSIONS
If the molar mass of a gas at STP is unknown ( in other words, you don’t have the formula for the gas)
Find the density of the gas and then combine the density with volume of 1 mol (22.4L) to find the mass of 1 mole

22. MULTIPLE CONVERSIONS
Ex: A 3.0 L bulb contains 2.2 g of a gas at STP. What is the molar mass of the gas?
Questions: p. 88 # 25-34

23. Helpful hints
Write out what is given in the question with its units(on left)
Write out what units your answer has to end up with(on right)
Using the different conversion factors you know, start multiplying to cancel out the units you don’t want, and keep the ones you want.

24. Homework
Page 88, 89, 90 #35, #36(b,d), #37 (d), #38(b), #39(d,f) #40(a,f) #41(a,d,f, j) #42(a,c,e,i,l,s) #43(a,d,g,i,k,o,g,r) You must practice these questions, or you will be lost for this unit ….