science 9

1. Chapter 8:
The Mole Concept
CHM 130
GCC Chemistry

2. Eggs come in dozens
12 eggs = 1 dozen
Atoms come in moles
6.02 x 1023 atoms = 1 mole = NA
NA is a ginormous number!
How big is it?
One mole of softballs would be the size of
the Earth!
8.1 Avogadro’s Number and the Mole

3.  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 on the Periodic Table.
 1 mole of C atoms is 12.01 grams
 1 mole of Na atoms is 22.99 grams
 What is the mass of one mole of Ne atoms?
The Mole

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

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

7. Molar mass tells us how much mass is in one
mole of substance.
Periodic Table masses are in units of (g/mol).
Very important – the units are grams per 1 mole,
not just grams
How many grams in one mole of:
 carbon?
 gold?
 sodium?
What do they all have in common?
They all have 6.02 x 1023 atoms!
12.01 g/mol
196.97 g/mol
22.99 g/mol
8.3 Molar Mass

8. Calculate the molar mass of barium hydroxide.
1.What is the formula?
2.Add up the mass for every atom.
Ba: 137.33 g/mol +
O: 2 (16.00) g/mol +
H: 2 (1.01) g/mol =
171.35 g/mol
Ba(OH)2
Molar Mass

9.  Use Molar Mass as (g/mol) or (mol/g)
 How many grams is 1.667 moles of oxygen
gas?
 1.667 mol O2 ( 32.00 g/mol) = 53.34 g O2
 How many moles is 45 grams of silver?
 45 g Ag ( mol/ 107.87 g) = 0.42 mol Ag
 How many grams is 0.0554 moles of water?
 0.0554 mol H2O (18.02g /mol) = 0.998 g H2O
8.4 Grams to Moles (Mole Calcs II)

10. 8.5 Molar Volume
(Volume of 1 mole of gas at STP)

11. 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

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

13. Density
d = = me
molar volu
mass
molar
volume
mass
Calculate the density of ammonia gas, NH3, at STP.
d = (17.04 g/mol ) / ( 22.4 L/mol ) = 0.761 g/L

14. 8.6 Mole Calcs III

15. Example
How many grams does 17.35 liters of
neon gas weigh at STP? How many
atoms is this?
17.35 L = 15.6 grams Ne












mol
1
g
20.18
L
22.4
mol
1














mol
1
atoms
10
x
6.02
L
22.4
mol
1 23
17.35 L = 4.66x1023 atoms Ne

16. 8.7 Percent Composition
= mass % of each element in a compound
You divide the total element molar mass
by the total compound molar mass.
% = (element / compound) x 100
%H = (2.02 g H / 18.02 g H2O) x 100 =
11.2% H
%O = (16.00 g O / 18.02 g H2O) x 100 =
88.79% O

17. Example Problem
Find the percent composition for TNT,
C7H5(NO2)3
Total molar mass is 227.15 grams per mole
% C = (84.07g / 227.15g) x 100 = 37.01% C
% H = (5.05g / 227.15g) x 100 = 2.22%H
% N = (42.03g / 227.15g) x 100 = 18.50%N
% O = (96.00g / 227.15g) x 100 = 42.26%O

18. Try at home
How many liters will 3.425 grams of
carbon dioxide gas occupy at STP? 1.74 L
How many molecules are in 3.425 grams of
carbon dioxide? 4.68 x 1022 molecules
What will be the mass of 3.0 x 1015
molecules of carbon dioxide? 2.2 x 10-7
grams

19. Self Test
Page 248
Try 1-7, 10-13
Answers in Appendix J

20. Chapter 8 Quiz
1) How many molecules are in 1.25 g of
copper?
2) What is the mass of 35.6 L of xenon gas at
STP?
3) What is the mass percent of carbon in aspirin
(C9H8O4)?