Chapter 1
What is Chemistry?
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It is a broad science that touches
nearly every aspect of life.
Most things lead to chemistry (water
ecology, farming, medicine, house
wife/mother, masonry …..
Why study chemistry?
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It plays a role in many areas of life
(knowledge is power).
Many occupations require this knowledge.
It is fun to know how things work.
It helps develop the mind (reasoning power
and observation skills). It is like weight
training for the mind.
It can be very beautiful (like great music or
art).
The Scientific Method
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We make an observation.
We ask a question.
We formulate a tentative explanation (a
hypothesis).
We design an experiment to test the
hypothesis.
We analysis the result and conclude if we
are right.
Report results and ask a new question.
How to design a good
experiment
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Experimental results are typically
compared to the normal situation.
The control is that trial of the
experiment in which everything is kept
normal. (The control is the standard.)
The variable is that one aspect that is
changed in each trial.
After many experiments and
observations may develop:
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A theory – It is a broad overview of
understanding that explains things.
(example: the molecular theory of
matter)
A natural law – is an observation that
nature always behaves the same way.
(example: mass is conserved in
chemical reactions)
The Math Tool Kit
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International system of units (SI)
– Length – meters (m)
– Mass – gram (g)
– Volume – liter (L)
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See page 18
Units can be increased or
decreased by using a prefix
Prefix
Nano
Micro
Milli
Centi
Deci
Kilo
Mega
Abbreviation
n
µ
m
c
d
k
M
Meaning
10-9
10-6
10-3
10-2
10-1
103
106
Scientific Notation
Place the decimal point behind the first
non-zero number and use a power of
ten to indicate the magnitude of the
number.
Change 1,230,000,000 to scientific
notation (1.23 x 109)
Change 0.0000001401 to scientific
notation (1.401 x 10-7)
Multiply the above two numbers
172.323
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Uncertainty in measurements
and calculations
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Exact numbers – definitions
(example 12 inches = 1 foot)
Inexact numbers – measurements
(example: 12.1 inches, 2.54 cm = 1 inch)
A measurement can be off by as much as ½ of
the smallest increment (the last digit is an
estimate)
(example: 1.2 + or - .05g) The true mass could
be closer to 1.15 or 1.25 than to 1.20g.
Percent Uncertainty in
Inexact Numbers
% uncertainty = uncertainty/value x 100
Example: mass of 1.2 g
% uncertainty = 0.05g/1.2g (100)
Uncertainty = 4.2%
Exact numbers have 100% certainty
Calculate the % uncertainty
in each of the following
measurements.
1.
111.1 grams
1.
2.
11 grams
1.
3.
4.5%
.11 grams
1.
4.
.045%
4.5%
Which value can you have the most
confidence in?
Reliability in
Measurement
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Precision – the smallest increment of
measurement, gives the same results
again and again
Accuracy – how close the value is to
the true value
Target Analogy
Significant Digits
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To reflect the degree of confidence
that we can have in our number, we
use rules in reporting the number.
These rules are the significant digit
rules.
The greater number of significant
digits, the lower the uncertainty and
the more confidence we have in the
number.
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See the Significant Figures sheet
The more significant digits, the more
confidence we can have in the number.
Complete the sig. digit worksheet.
Why use scientific
notation?
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It is good for very large or very small
numbers.
It is also the best way to show the
number of significant digits.
Complete practice worksheets.
(Factor-label method)