Chemistry in Our Lives

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Chemistry in Our Lives

• Chemistry and Chemicals

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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
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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

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Everything in our lives from materials to life
involve chemistry

• glass (SiO2)n
• metal alloys
• chemically treated water
• plastics and polymers
• baking soda, NaHCO3
• foods
• fertilizers and pesticides
• living beings

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Chemicals in Toothpaste
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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

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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.

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Units of Measurement
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In chemistry quantities are measured experiments
are performed results are calculated use numbers
to report measurements, results are compared to
standards.
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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.
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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)
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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

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

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

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• 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

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• 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
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• 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?
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• 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

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• 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

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Scientific Notation

• A number in scientific notation contains a
  coefficient and a power of 10.
• coefficient power of ten
  coefficient power of ten
• 1.5 x 102 7.35
  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

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10-3/105
10-8
102
10-3105
105
100000 0.001 100000.001
10-3 105
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Measurements
What is the length of this piece of wood?
What is the first digit? Any uncertainty in the
digit?
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What is the second digit? Any uncertainty in this
digit?
4.5
What is the third digit? Any uncertainty in this
digit?
4.56
Definition of a significant figure Significant
digits include all digits with no uncertainty
plus one estimation
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• . l8. . . . l . . . . l9. . . . l . . . . l10. .
  cm
• 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
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Number of Significant Figures

• Measurement
• 38.15 cm
• 5.6 ft
• 120.55 m
• 0.0055 in
• 1200 m

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2
5
2
2
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A. Exact numbers are obtained by 2.
counting 3. definition B. Measured numbers
are obtained by 1. using some measuring tool

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• Classify each of the following as exact (E) or
• measured (M) numbers. Explain your answer.
• A. __ Gold melts at 1064 C.
• B. __ 1 yard 3 feet
• C. __ The diameter of a red blood cell is 6 x
  10-4 cm.
• D. __ There are 6 hats on the shelf.
• E. __ The atom sodium has 11 protons and 12
  neutrons.

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Significant Figures

• In calculations
• Answers must have the same number of significant
  figures as the measured numbers.
• Calculator answers must often be rounded off.
• Rounding rules are used to obtain the correct
  number of significant figures.

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Rounding Off

• When the first digit dropped is 4 or less, the
  retained numbers remain the same.
• To round 45.832 to 3 significant figures
• drop the digits 32 45.8
• When the first digit dropped is 5 or greater,
• the last retained digit is increased by 1.
• To round 2.4884 to 2 significant figures
• drop the digits 884 2.5 (increase by 0.1)

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Multiplication and Division

• When multiplying or dividing use
• the same number of significant figures (SF) as
  the measurement with the fewest significant
  figures
• Example
• 110.5 x 0.048 5.304 5.3
• 4SFs 2SFs calculator 2SFs

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Addition and Subtraction

• When adding or subtracting, use
• the same number of decimal places as the
  measurement with the fewest decimal places
• 25.2 one decimal place
• 1.34 two decimal places
• 26.54 calculated answer
• 26.5 final answer (with one decimal
  place)

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For each calculation, round the answer to give
the correct number of decimal places. A. 235.05
19.6 2 1) 257 2) 256.7 3)
256.65 B. 58.925 18.2 1) 40.725 2)
40.73 3) 40.7




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1m/100cm 1 1m/1000mm 1

• An equality
• states the same measurement in two different
  units
• can be written using the relationships between
  two metric units
• Example 1 meter is the same as 100 cm and 1000
  mm.
• 1 m 100 cm
• 1 m 1000 mm

1 100cm/1m 1 1000mm/1m
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volume has the dimensions of length cubed
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• Several equalities can be written for mass
• 1 kg 1000 g
• 1 g 1000 mg
• 1 mg 0.001 g

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Some Common Equalities



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• An injured person loses 0.30 pints of blood. How
  many milliliters of blood would that be?

0.30pt1qt/2pt 0.15qt
0.15qt946mL/qt 141.9 mL 140 mL
0.30pt2pt/1qt 0.60pt2/qt
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• If a person weighs 200 pounds, how many kiograms
  does the person weight?
• 200 lb1 kg/2.2 lb 90.9 kg
• 200 lb2.2 lb/1 kg 440 lb2/kg

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• If the thickness of the skin fold at the
• waist indicates an 11 body fat, how
• much fat is in a person with a mass
• of 86 kg?
• 11 fat means 11kg/100kg body weight
• 86 kg x 11 kg fat 9.5 kg of fat
• 100 kg

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Density
Density compares the mass of an object to its
volume is the mass of a substance divided by its
volume Density expression D mass
g or g g/cm3
volume mL cm3
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Osmium is a very dense metal. What is its density
in g/cm3 if 50.0 g of osmium has a volume of 2.22
cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111
g/cm3
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• The density of the zinc object can be calculated
  from its mass and volume.

d 68.6g/(45.0-35.5)mL 68.6g/9.5 mL d 7.2
g/mL