1. The Mole Concept
Chapter 9
CHM 130
GCC

2. 9.1 Avogadro’s Number and The Mole
Eggs come in dozens = convenient
12 = dozen
Atoms come in moles
6.02 x 1023 = mole = NA
NA is just a super large number

3. The Mole One mole of softballs would be the size of the Earth!
But atoms are so tiny that one mole of atoms is about a handful.
The mass of a mole of atoms = the atomic mass in grams in the Periodic Table
1 mole of C atoms is grams
1 mole of Na atoms is grams

4. Mole Examples
sugar
water
lead
mercury
copper
sulfur
sodium chloride

5. 9.2 Avogadro’s number : 6.02 x 1023 atoms or mlcls or 1 mol
1 mol x 1023atoms or mlcls
1. How many calcium atoms are in moles of calcium:
0.250 mol Ca (6.02 x 1023 atoms/mol) = 1.51 x 1023 Ca atoms
2. Calculate the moles of 3.75 x 1027 molecules of oxygen gas:
3.75 x 1027 mlcls O2 ( mol/6.02 x 1023 mlcls) = 6230 mol O2

6. 9.3 Molar Mass: Periodic Table masses are in ( g /mol )
How many grams in one mole of
carbon?
gold?
sodium?
Note = these are all 6.02 x 1023 atoms!
12.01 g/mol
g/mol
22.99 g/mol

7. Molar Mass: 137.33 + 2 ( 16.00) + 2 ( 1.01 ) = 171.35 g / mol
Calculate the molar mass of barium hydroxide.
What is the formula?
Add up the mass for every atom.
Ba(OH)2
( 16.00) ( 1.01 ) = g / mol
Very important – the units are grams per 1 mole, not just grams

8. 9.4 Grams to Moles & Vice Versa
Use Molar Mass as (g / mol) or (mol / g)
How many grams is moles of oxygen gas?
How many moles is 45 grams of silver?
How many grams is moles of water?
1.667 mol O2 ( g/mol) = g O2
45 g Ag ( mol/ g) = 0.42 mol Ag
mol H2O (18.02g /mol) = g H2O

9. 9.5 Molar Volume (V of 1 mole at STP)

10. STP is Standard Temperature and Pressure
Volume of 1 mole of gas
Gases are mostly empty space so they ALL have the same volume despite different mass
22.4 L per 1 mole of any gas at STP
STP is Standard Temperature and Pressure
0°C and 1 atm

11. For Gases only at STP: 22.4 L / 1 mol or 1 mol / 22.4 L
What is the volume of 1.25 moles of gas at STP?
1.25 mol ( 22.4 L / 1 mol) = 28.0 L gas
What is the mass of 4.50 L of chlorine gas at STP?
4.50 L Cl2 (mol / 22.4L) (70.90 g/mol) = 14.2 g Cl2

12. d = = Density Calculate the density of ammonia gas, NH3, at STP.
d = (17.04 g/mol ) / ( 22.4 L/mol ) = g/L

13. 9.6 Mole Calcs

14. Example
How many grams does liters of neon gas mass at STP? How many atoms is this?
17.35 L = 15.6 grams Ne
17.35 L = 4.66x1023 atoms Ne

15. Percent Composition = mass % of each element in a compound
Water is basically 11% H and 89% O
You divide the total element molar mass by the total compound molar mass.
%H = (2.02 g H / g H2O) x 100 = 11.2% H
%O = (16.00 g O / g H2O) x 100 = 88.79% O
Note the %’s should add up to 100% total

16. Example Problem Find the percent composition for TNT, C7H5(NO2)3
Total molar mass is grams per mole
% C = (84.07g / g) x 100 = 37.01% C
% H = (5.05g / g) x 100 = 2.22%H
% N = (42.03g / g) x 100 = 18.50%N
% O = (96.00g / g) x 100 = 42.26%O

17. Try at home
How many liters will grams of carbon dioxide gas occupy at STP? L
How many molecules are in grams of carbon dioxide? x 1022 molecules
How many grams will 3.0 x 1015 molecules of carbon dioxide mass? x 10-7 grams

18. Self Test
Page 258
Try 1-7, 10-13
Answers in Appendix J