Introduction to chemistry: Scientific method, measurement, basic properties of matter Ms. Buroker

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Introduction to chemistryScientific
method, measurement, basic properties of
matterMs. Buroker
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LESSON TOPICS
Why Chemistry?
An Introduction to Chemistry
The Scientific Method
The Metric System
Measurement Importance of Numbers
Precision and Accuracy
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What is Chemistry?

• A basic definition of chemistry would be, the
  study of matter and the changes it undergoes.
• Matter- Anything that has mass and takes up
  space.

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MAIN BRANCHES OF CHEMISTRY

• Organic Chemistry ? the study of most carbon-
  containing compounds
• Inorganic Chemistry ? the study of non organic
  compounds many of these are actually organic
  compounds bound to metal.
• Physical Chemistry ? the study of the properties
  and changes of matter and their relation to
  energy.
• Analytical Chemistry ? the identification of the
  components and composition of materials.
• Biochemistry ? the study of substances and
  processes occurring in living things.
• Theoretical Chemistry ? the use of mathematics
  and computers to understand the principles behind
  observed chemical behavior and to design and
  predict the properties of new compounds.

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SCIENTIFIC METHOD

• The scientific method is not a rigid set of
  rules, but a general guide for investigation or
  logical approach to finding answers to questions.
• Curiosity or a quest for knowledge
• Design and do experiments, collect data and
  information, establish facts, and make
  observations
• Organize and find relationship between
  information or data. Formulate a law, a
  statement of the relationships between facts,
  data, and observations.

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SCIENTIFIC METHOD CONTINUED

• 4. Draw conclusions from the observation, data,
  and facts. Formulate a hypothesis, a tentative
  explanation of a scientific law.
• 5. Design new experiments based on the
  hypothesis, and collect more data, establish more
  facts, and make more observations.
• 6. Update laws and hypothesis, ask new questions,
  and recycle to step 5.

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Scientific Research
Just a Quick Note Qualitative Data
Quantitative Data

• Pure Research to gain knowledge for the sake
  of knowledge itself.
• Applied Research research undertaken to solve
  a specific problem.
• NOTE
• Science and Technology are NOT the same thing!
• Where science includes knowledge in whatever
  discipline youre in technology is the
  application of that knowledge for practical
  purposes.

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Measurements

• Science involves making observations and
  measurements. These measurments involve two
  things a number and a unit.
• 25.4 g

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Units of Measurement

• We have an international system of measurement
  the SI system. This is a system of measurement
  that the world has agreed upon.
• We need to be aware however that there is
  actually one more system called the cgs system
  which stands for centimeter, gram, second.

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SI Base Units
Some Basic Properties cgs (subset of the metric system) SI System other
Length or distance centimeter meter In, yds, mi
Time seconds seconds hours, days
Mass grams kilograms lb, oz
Kinetic Energy Erg Joule
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Derived Units

• Derived units are combinations of base units
  such as mass and volume.
• Volume the space occupied by an object
• Density a ratio of mass to volume

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Unit Consistency

• Express all units in the same unit of the system
  
• Kinetic Energy ½ M V2

Kinetic Energy Ergs cgs Joules SI
Mass grams cgs kg SI
Velocity cm/s cgs m/s SI
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UNIT CONVERSIONS

• It is important, especially for unit
  consistency, that you are able to move back and
  forth between units of measurement.
• Conversion Factors are NOT scary
• they are simply ratios that come from two things
  of different units which are equal to one another
  in magnitude!!

The chemistry is knowing where things go the
solving is just algebra!
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Dimensional Analysis

• The technique we use that allows us to convert
  from one unit of measurement to another, is
  dimensional analysis.
• Conversion factor a ratio of equal values used
  to go from one unit to another
• Example 1 foot 12 inches
• Can be written as 1 foot
  12 inches

We Use This
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Rules for Dimensional Analysis

1. ALWAYS start with the _____________ !!!
2. Draw a _____________ sign and a line
3. Place the unit to be canceled on the bottom
4. Place a _____________ on the line you have drawn
5. Cross out units and see what you have left.
6. Do the math!

B
A
/
x
---------
A
/
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Lets try an example

• Let s convert 32.5 inches to feet.
• How many seconds are in 82.95 minutes?
• Convert 65 miles per hour to kilometers per
  second. (0.625 miles 1 Km)
• Conversions with prefixes are done in exactly the
  same manner, you just have to know the prefixes!!

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Prefixes
These smaller units are fractions of the base.
For example a centimeter is a 100th of a meter.
These larger units are multiplications of the
base. For example a kilometer is 1000 meters.
Kilo Hecto Deca Base deci centi milli
1000 100 10 1 1/10 1/100 1/1000
micro nano pico
1/1000000 (1 x 10-6) 1/1000000000 (1 x 10-9) 1/1000000000000 (1 x 10-12)
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Numbers

• There are two types of numbers in the world
• 1.) Exact
• Example Sample size or n
• 2.) Nonexact measurments

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Measurement and Significant Figures

• All measurements have some uncertainty
• the accuracy and precision of the measuring
  device
• the skill of the operator
• the uncertainty principle

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ACCURACY VS. PRECISION

• Accuracy How closely the measured value is to
  the true value
• Precision How closely the measured values are to
  one another

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MEASURE OF ACCURACY
I correct value measured value I
X 100
Error
correct value
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Uncertainty
There is uncertainty in every measurement we
take. We are limited not only by the instruments
we use, but also by our own physical limitations.
Scientists have devised a way to communicate our
limitations in a way that we can all have an
idea to how much uncertainty there is in a number
simply by looking at it!
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Significant Figures

• Scientist use significant figures to determine
  how precise a measurement is.
• Significant digits in a measurement include all
  of the known digits plus one estimated digit .

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For example

• Look at the ruler below
• What would be the measurement in the correct
  number of sig figs?

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Lets try this one

• Look at the ruler below
• What would be the measurement in the correct
  number of sig figs?

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The same rules apply with all instruments

• Read to the last digit that you know
• Estimate the final digit

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Lets try graduated cylinders

• Look at the graduated cylinder below
• What would be the measurement in the correct
  number of sig figs?

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One more graduated cylinder

• Look at the cylinder below
• What would be the measurement in the correct
  number of sig figs?

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Rules for Significant figuresRule 1

• All non zero digits are ALWAYS significant
• How many significant digits are in the following
  numbers?

274 25.632 8.987
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Rule 2

• Zeros are ONLY significant if they meet the
  following criteria
• 1.) they are between non-zero digits
• 2.) they are at the end of a number AND to the
  right of the decimal
• How many significant digits are in the following
  numbers?

504.0 6002 9.077
5.00 0.00361 2.0100
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Rules Continued

• All zeros that act as place holders are NOT
  significant these are zeros in front of the
  number or zeros at the end of a number with no
  decimal.
• Numbers with zeros at the end and no decimal can
  be made significant by adding a decimal 2000.
  or 30.

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For example
How many significant digits are in the following
numbers?

1. _____________
2. _____________
3. _____________
4. _____________
5. _____________

1. 0.0002
2. 6.02 x 1023
3. 100.000
4. 150000
5. 800

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Rule 5

• All counting numbers and constants have an
  infinite number of significant digits in other
  words, you do not have to worry about them when
  performing calculations.
• For example
• 1 hour 60 minutes
• 12 inches 1 foot
• 24 hours 1 day
• There are 30 students in the class

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How many significant digits are in the following
numbers?

1. 0.0073
2. 100.020
3. 2500
4. 7.90 x 10-3
5. 670.0
6. 0.00001
7. 18.84

1. _____________
2. _____________
3. _____________
4. _____________
5. _____________
6. _____________
7. _____________

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RULES FOR THE COMBINATION OF SIGNIFICANT DIGITS

• 1. Addition and Subtraction ? Round to the least
  decimal place
• Add 23.67 9.5 33.17 ? 33.2
•  
• 2. Multiplication and Division ? Round to the
  least significant digit
• (2.34 x 3.2)/ 5.22 1.434482 ? 1.4
•  

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What happens when to have the appropriate amount
of significant figures, you need to round???

• 200.99 (want 3 SF)
• 18.22 (want 2 SF)
• 135.50 (want 3 SF)
• 0.00299 (want 1 SF)
• 98.59 (want 2 SF)

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What happens when to have the appropriate amount
of significant figures, you need to use
Scientific notation???
Place the following numbers in scientific
notation with 3 SFs

1. 99.343
2. 4000.1
3. 0.000375
4. 0.0234
5. 94577.1