Unit 1 Chemistry, the Quantitative Science

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Unit 1 Chemistry, the Quantitative Science

• Addison-Wesley Chapters 1, 3, 4
• What is chemistry?
• The study of all substances and the changes that
  they undergo
• Central to almost all other sciences

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Chemistry is an old science

• It began as early as 400 BC in China.
• The Chinese made fireworks and gunpowder.
• This website has a lot of information about
  fireworks.
• Old Demo.

3
Chemistry comes of age in the late 1700s.

• It was refined by Antoine Lavoisier who made it
  an experimental science.
• He was beheaded for his efforts.

scienceworld.wolfram.com/ biography/Lavoisier.html

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Lavoisier is considered the father of the
scientific method.
noe-education.org/ D115.php3
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It is very important today.
http//www.thetech.org/nmot/detail.cfm?ID33STORY
3stawardDateqt1996

• New Demo

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The Scientific Method

• The steps of the scientific method include
  observing, making a hypothesis, testing the
  hypothesis, and developing a theory.

phyun5.ucr.edu/.../ Physics7/Notes_www/node6.html
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Observations

• An observation is a simple statement of what is
  seen.
• An interpretation is a conclusion about an
  observation.
• Example Bubbles are observed but should not be
  called oxygen or air.

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Experimental Setup

• Hypothesis is a proposed explanation for an
  observation.
• An experiment is a procedure used to test a
  hypothesis.
• Control the experiment with all conditions
  defined. Used as a means of comparison.
• Variable Factor that is changed in an
  experiment.

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Variables

• The independent variable is the variable or
  condition that is changed during the experiment.
• The dependent variable is the variable or
  condition that is observed or recorded.

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Theory vs. Law

• A theory is an explanation for a broad set of
  observations that has withstood the test of time.
• A law describes the way that nature behaves, but
  doesnt include an explanation.
• Name an example of each.

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Communication

• This has been added as the last step of the
  scientific method.
• Why?

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Metric System

• Established in France in 1790
• Revised in 1960, called SI system
• Accepted throughout the world
• Mathematically elegant
• Why doesnt the US accept it?

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7 Base units

• Meter measure of distance m
• Kilogram measure of the amount of matter kg
• Kelvin temperature K
• Second time s
• Mole number of atoms of a subtance mol
• Candela luminous intensity cd
• Ampere electric current A

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Metric Definitions

• Length Distance light travels in a vacuum in a
  certain amount of time.
• Mass amount of matter in an object. The
  standard kilogram is found in a vault in France.
• Time event that is measured is the vibration of
  a cesium atom.

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Mass vs. Weight

• Weight is the result of the gravitational
  attraction of a large body (like the earth) to a
  smaller body (like you). It can vary as you
  travel in the universe. Mass is the amount of
  matter in an object and remains constant.
• The derived Metric unit of weight (or force) is
  the Newton.
• Should Weight Watchers be called Mass
  Watchers?

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Derived Units

• Area amount of surface cover in two dimensions
• Length X width units are m2
• Volume Amount of space occupied by matter
• Volume (length X width X height) units are m3

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The Liter
Chemists needed a smaller volume. 1000 cm3 1
liter 1000 ml 1cm3 1 ml 1 cc Also called
1 dm3
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Prefixes
coke.physics.ucla.edu/ laptag/mchs/
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Dimensional Analysis or Factor-Label Method

• Best way to convert metric and do most chemistry
  problems.
• Multiplying by 1 does not change value of a
  number.
• Use conversion factors equivalent to 1 to get
  the unit that you want.
• Convert 40 km to cm.
• Puzzle

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Multi-step Problems

• Dimensional Analysis!
• Start with the given and use as many factors as
  necessary until you have the correct unit.
• How many seconds in 2 centuries?

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Uncertainty in measurement

• Counting numbers are perfect how many students
  in this class?
• All measurements have some uncertainty, depending
  upon the instrument used.
• For any instrument, you record all digits you can
  read plus one eyeballed digit.
• These are called significant digits.
• Ruler Activity

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Why bother?

• Solution story
• Duck story
• Cartoon
• 99.9 sheet of facts

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Significant Digits Rules for Written Measurements

• All digits 1-9 are significant. (567 m)
• All zeroes between digits 1-9 are significant.
  (30.4 cm)
• All zeroes that are only placeholders are not
  significant. (300 kg) or (0.003 mg)
• Zeroes that are after digits 1-9 after the
  decimal point are significant. (56.450 ml)
• Lets practice

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Trick
Determine if number has a decimal point absent
(Atlantic) or present (Pacific). Drive through
the number starting from the correct side. Count
all digits as soon as you hit your first digit 1
9.
P 32400
A
.0098700
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How good is your measurement?

• Accuracy how close is your measurement to the
  accepted value? We will learn a method to record
  this.
• Precision how repeatable is your value?
• Basketball example

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How accurate are you?

• Percent Error calculation
• Used when a known value has been determined
• Percent error /measured accepted/
• accepted

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Communicating Uncertainty

• Measurements are often written with a plus or
  minus symbol to express error.
• Example 87.97 /- 0.01 cm
• This may simply be written on the instrument.

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Operations with measurements

• You must determine the number of sig figs in each
  measurement before doing any operations.
• Then you must follow the rules for operations.

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Multiplication and Division

• Do the operation and round answer to the number
  of sig figs found in the measurement with the
  least number of sig figs.
• Density example.
• Remember counting numbers and equivalents have
  an infinite number of sig figs.
• Try one

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Addition and Subtraction

• Line up all numbers and do the operation.
• Round the answer after the decimal place only!
• Round the answer after the decimal point to the
  number of sig figs in the measurement with the
  least number of sig figs after the decimal point.
• Try one

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Scientific Notation

• Significant digits are all shown in the first
  fatcor in a measurement written in scientific
  notation.
• 4.00 X 104 cm has 3 sig figs
• All measurements should be written in scientific
  notation, but wont be.

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Riddle

• What weighs more, a pound of lead or a pound of
  feathers?
• What is the difference?

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Density

• The ratio of the mass of an object to its volume.
• Units are g/cm3 g/ml g/l kg/m3
• Equation d m/v
• Practice solving for any variable.

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Water Displacement

• The volume of irregular objects is often found by
  this method.
• Place water in a graduated cylinder.
• Read the volume at the bottom of the meniscus.
• Place object in water.
• Read the volume again.
• Subtract for volume of object.

http//www.howe.k12.ok.us/jimaskew/labeq3.htm
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Why do objects float?

• Archimedes Principle says that objects float when
  they can displace their own mass.
• If density of object is the same or less than
  that of the liquid, it will be able to displace
  entire mass and it will float.
• If density of object is greater than the liquid,
  when it has displaced its volume it has not
  displaced its mass, so it will sink.

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Archimedes Principle

• This website is a good interactive for
  determining if an object will float.
• http//www.seed.slb.com/en/scictr/lab/buoy_exp/buo
  yancy.html

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Graphing Basics

• Title
• Label each axis with proper units
• Use a scale for each axis that uses at least half
  of the page
• Use (0,0) if this makes sense for the data
• Plot points
• Draw best-fit line or curve