Chemistry and chemicals

Chemistry in Our Lives
Chemistry and Chemicals


What is chemistry?

Chemistry is the study of substances in terms of
Composition

What a material it made of

Structure

How the elementary particles are put together

Properties

The characteristics of the material

Reactions

How it behave with other substances


Chemical reactions happen when
• a car is started
• tarnish is removed from silver
• fertilizer is added to help plants
grow
• food is digested
• electricity is produced from

burning natural gas
• rust is formed on iron nails


Everything in our lives from materials
to life involve chemistry
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glass (SiO2)n
metal alloys
chemically treated water
plastics and polymers
baking soda, NaHCO3
foods
fertilizers and pesticides
living beings


Chemicals in Toothpaste


The Scientific Method
The scientific method is the

process used to explain
observations in nature.
The method involves:
• making observations
• forming a hypothesis
• doing experiments to test
the hypothesis


Everyday Scientific Thinking
• Observation: The sound from a CD in a CD
player skips.
• Hypothesis 1: The CD or player is faulty.
• Experiment 1: When the CD is replaced with another
one, the sound from the second CD is
OK.
• Hypothesis 2: The original CD has a defect.
• Experiment 2: When the original CD is played in another
player, the sound still skips.
• Theory:
The experimental results suggest that
the original CD has a defect.


Units of Measurement


In chemistry:
quantities are measured
experiments are performed

results are calculated
use numbers to report measurements,
results are compared to standards.


In a measurement of the thickness
of the skin fold at the waist,
calipers are used.
A measuring tool is used to
compare some dimension
of an object to a standard.


In every measurement, a number must be followed by a unit
to have any meaning.
Observe the following examples of measurements:
Number and Unit
35 m (meter)
0.25 L (liter)
225 lb (pound)
3.4 h (hour)


The Metric System (SI)
The metric system and SI (international
system) are
 related decimal systems based on 10
 used in most of the world
 used everywhere by scientists

Length
 is measured using a meter stick
 uses the unit meter
(m) in both the metric and SI systems


The unit of an inch
 is equal to exactly
 2.54 centimeters in
 the metric system
1 in. = 2.54 cm


Volume
 is the space occupied
 by a substance
 the unit of volume is the
liter (L) in the metric
system
1 L = 1.06 qt


The mass of an object
 is a measure of the quantity of material it contains
 the unit gram (g) or kilogram (1000 g) is used

What is the difference between mass and weight?
Weight is the result of the action of gravity on mass. Your weight
on the moon would be a lot less even though your mass would

remain the same
Despite this important difference, we will use these two terms interchangeably


The temperature
 indicates how hot or cold a
substance is
 the Celsius (°C) scale is used
in the metric system
 the Kelvin (K) scale is also
used
 18 °C is 64 °F on this
thermometer
On the °C scale, the melting point of ice is 0 °C and boiling point of
water is 100 °C
What is heat or cold? What does temperature really measure?


Time measurement
 the unit second (s) is
used in the metric
system.
 Time is based on an
atomic clock that uses a
frequency emitted by
cesium atoms


Scientific notation
 is used to write very large or very small numbers

 the width of a human hair (0.000 008 m) is written
8 x 10-6 m
 a large number such as 4 500 000 s is written
4.5 x 106 s


Scientific Notation
 A number in scientific notation contains a coefficient and a
power of 10.

coefficient

1.5

power of ten

x

102

coefficient

7.35

power of ten

x 10-4

 To write a number in scientific notation, the decimal point is
placed after the first digit.

 The spaces moved are shown as a power of ten.
52 000. = 5.2 x 104
0.00378 = 3.78 x 10-3
4 spaces left

3 spaces right


10-3/105 =

10-8

10-3*105 =

102

10-3 +105 =

105

100000 + 0.001 = 100000.001


Measurements

What is the length of this piece of wood?
What is the first digit? Any uncertainty in the digit?
What is the second digit? Any uncertainty in this digit?
What is the third digit? Any uncertainty in this digit?

4
4.5
4.56

Definition of a significant figure:
Significant digits include all digits with no uncertainty plus one estimation


• . l8. . . . l . . . . l9. . . . l . . . . l10. . cm
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What is the length of the red line?
1) 9.38 cm
2) 9.39 cm
3) 9.40 cm
9.38, or 9.39, 9.40 is less likely



Measurement

Number of
Significant
Figures

38.15 cm

4

5.6 ft

2

120.55 m

5

0.0055 in
1200 m

2
2