Transcript The Math of Chemistry

The Math of Chemistry
Factor-Label Method
the Mole
gram formula weight
Avogadro Number
Scientific Notation
Percent Composition
Empirical Formulas
Hydrates
Begin working on HW 11 and 12
• To convert units, you must write down what
you know, then use a conversion factor to
convert it to what you want to know.
0.32 g = ____________mg
use 1000 mg = 1 g
0.32 g
1000 mg
=
1g
32 mg
What if you only know a similar
conversion factor, not the exact one
you
need?
3
3
• 0.436 m = _____________cm
– use 1m = 100 cm; then cube both sides.
– 13 m3 = (100)3 cm3
– 1 m3 = 1,000,000 cm3
0.436 m3
100000 cm3
436000 cm3
or
4.36 x 105cm3
=
1 m3
This procedure is called the factor label method
Use page 29 in your book to help
you do problem 28 page 196
• On the blackboard, three students can earn a
free homework pass by correctly solving
and carefully explaining how to do #28 a
and b OR #28 f or g
Quiz: Factor Label Method
convert the following:
1. 30 cm = ______m
1
2. 3600 sec =____hours
3. 10 cm3 = _____ m3
30cm (1 m)
(100 cm)
= 0.30 m
3600sec (1 min)(1hour)
(60 sec)(60 min)
10cm3 (13 m3) = 0.01 m3
(1003 cm3)
Molecular and Formula Mass
• Instead of using single atoms with masses on the order
of 10-24g, we use moles
– one mole = 1 Avogadro number of particles
– 6.02 x 1023 particles = 1 Avogadro number.
• We can use the numbers on the periodic table as either
atomic mass units or grams. When we use them as
amu we are talking about quantities too small to
measure.
• When we use moles, we are talking about 6.02 x 1023
atoms or ions or formula units or molecules.
Find the gfw of cyclopentane
C5H10
55 CC = 5(12.0amu)
10
10HH = 10 (1.00amu)
5(12.0) + 10 (1.00)
= 60.0 + 10.0
= 70.0 amu or
g/mole
27
amu
14
amu
Find the gfw of AlN
• First, identify the elements, and how many
1 Al and 1 N
of each are in the compound.
• Then find the atomic masses on the periodic
table
• Then, multiply how many of an atom by
how much it weighs.
1(27.0) and 1(14.0)
• Finally, find the sum of all the pieces of the
compound.
1(27.0) + 1(14.0)
41.0 g
In Groups
• You are responsible for finding the gram
formula masses of each compound on the
sheet of paper. Points will be awarded for
the groups who have successfully calculated
the greatest number of gfw.
• Students will come up to the board to
explain how they found the gfw of a
substance. Points will be awarded for the
quality of the explanation.
Quiz: Find the gfw for the following
compounds…
1. NaCl
2. Al2S3
3. Ca3(PO4)2
1. 23 + 35 = 58 g/mole
2. 2(27) + 3(32) =
54 + 96 =
150
3. 3(40) + 2(31) + 8(16)
= 120 + 62 + 128
= 310 g/mole