Section 12.1: Counting Particles of Matter
Is it practical to count out 200 grains of rice, or
200 pieces of macaroni?
No Way!
We sell these items by the pound. How would
we be able to calculate how many items are in a
container without counting?
There is!
At your table, discuss a method to figure out
how many items are in each bag, without
counting. What information would you need?
How many candy hearts are in the jar?
What you need; the data:
Mass of the empty jar (with stopper) =
209.624 g
Mass of the full jar (with stopper)= 396.227 g
Average mass of one candy heart= 1.92 g
How many atoms are in 1.0079 g of Hydrogen
if the average mass of
one atom is 1.67425 x 10-24 g?
What you need:
Total mass
• Mass of one atom
What number do you get?
6.02 x 1023 atoms of H
•
The study of the relationships between the
macroscopic quantities like mass and volume,
and the submicroscopic quantities like
number and mass of the atoms involved in a
chemical reaction.
Chemists cannot count individual items
because the particles of matter are too small
and too numerous- so we use this process.
The group or unit of measure that we use in
chemistry to count numbers of atoms, ions,
molecules or formulas units of a substance
(elements or compounds)
Mole Map
• http://www.youtube.com/watch?v=4QiGVqK7AS
U
•
https://www.youtube.com/watch?v=TEl4jeETVm
g&list=PLKEmXepzBsY9Zx4EHN27HHSQyvb4Xysb
4&index=6
6.02 x 1023
•
•
•
This HUGE quantity represents the number of
particles in one mole of ANY substance. It is
just a number!
A mole can be analogous to a dozen, a pair, a
century…you know how many individual parts
there are in each one of these measurements,
right?
12, 2, 100…a mole is just A LOT more.
Video
The mass in grams of one mole of an
element or a compound! (g/mol)
For elements, it is the atomic mass in grams
– One atom of magnesium = 24.31 u (atomic mass
units )
– One mole of magnesium = 24.31 g/mol
For compounds, it is the sum of all the masses of
each element in the compound’s formula
One mole
MgSO4 = 24.31 + 32.07 + 4(16.0) = 120.4 g/mol
These are not hard to calculate, because essentially the
value of each is the same. It is the units that are
different!
•
Formula Mass is a term used for IONIC compounds
– NaCl has a FORMULA mass of 58.45 u and a MOLAR mass
of 58.45 g/mol
– ~ Same quantity, different unit
Ex. CaCl2
Ca: 1 x 40.1 = 40.1
Cl: 2 x 35.5 = 71
Formula mass = 111.1 u
Molar mass = 111.1 g/ mol
•
Molecular Mass is a term used for COVALENT
compounds
– C2H6 has a MOLECULAR mass of 30.1 u and a
MOLAR mass of 30.1 g/mol
Ex: C2H6O
C: 2 x 12 = 24
H: 6 x 1 = 6
O: 1 x 16 = 16
Molecular mass = 46 u
Molar mass = 46 g/ mol
•
•
When solving problems like the following, you
must use DIMENSIONAL ANALYSIS (Factor
Label Method).
Steps
grams
↔
moles
Molar mass
↔
“stuff”
Avogadros #
68 g NH3 = ? mol
1 N = 1 x 14.007 = 14.007 g
3 H = 3 x 1.008 = 3.024 g
14.007 + 3.024= 17.031 g NH3
68 g NH3 x
1 mole NH3 = 3.99 mol NH3
17.031 g NH3
17.5 g CuO = ? mol
1 Cu = 1 x 63.546 = 63.546 g
1 O = 1 x 15.999 = 15.999 g
63.546 + 15.999 = 79.545 g CuO
17.5 g CuO x 1 mole CuO = 0.22 mol CuO
79.545 g CuO
0.550 mol F2 = ? g
2 F = 2 x 18.998 = 37.996 g
0.550 mol F2 x
37.996 g F2
1 mole F2
= 20.90 g F2
2.35 mol BaI2 = ? g
1 Ba = 1 x 137.33 = 137.33 g
2 I = 2 x 126.90 = 253.8 g
137.33 + 253.8 = 391.13 g
2.35 mol BaI2 x 391.13 g BaI2 = 919.16 g BaI2
1 mole BaI2
10.7 g Li = ? atoms
10.7 g Li x 1 mole Li X 6.02 x 1023 atoms Li
6.941 g Li
1 mole Li
= 9.28 x 1023 atoms Li
144.6 g W = ? atoms
144.6 g W x 1 mole W X 6.02 x 1023 atoms
W
183.85 g W
1 mole W
= 4.73 x 1023 atoms W
1. Does 50.0 g S or 50.0 g Sn represent a greater #
of atoms?
50.0 g S x 1 mole S X 6.02 x 1023 atoms S
32.066 g S
1 mole S
= 9.39 x 1023 atoms S
50.0 g Sn x 1 mole Sn
X 6.02 x 1023 atoms Sn
118.710 g Sn
1 mole Sn
•
= 2.54 x 1023 atoms Sn
Sulfur is smaller- has a greater number of atoms
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What mass of water must be weighed to obtain
7.50 mol of H2O
How many moles are in 17.5g copper (II) oxide

How many molecules are in each sample?
89g nitrogen monoxide
10.8g boron trifluoride

What is the molecular mass of aspirin (C9H8O4)
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