Unit 1 Scientific Method Measurement

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Unit 1Scientific MethodMeasurement

• Chem 1
• Fall 07

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Scientific Method
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Scientific Method (cont.)

• People often confuse
• Observations Hypotheses
• An observation
• Is information collected with the senses
• A hypothesis
• Is a theory about the natural world that needs to
  be tested

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Scientific Method (cont.)

• People also often confuse
• Controls Variables
• A control is
• A trial that duplicates all conditions except the
  variable being investigated
• A variable is
• The thing being tested

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Practice Problem 1

• Identify the following as an observation or a
  hypothesis
• 1. Wearing tennis shoes will make one run faster.
• 2. The tennis shoes are black and red.
• 3. The Bunsen Burner flame is 1400C and is blue.
• 4. People who take good notes will do better on
  tests.

Hypothesis
Observation
Observation
Hypothesis
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Types of Observations

• Scientists make observations all the time.
• Theres two types
• Qualitative
• Quantitative
• To remember the difference, look at their root

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Qualitative Observations

• Qualities of the reaction, object, etc.
• Example
• The copper (II) sulfate is blue
• The nail is rusty
• Gas was given off

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Quantitative Observations

• Quantity numbers
• Mass, a number of paper clips, volume
  measurements, molar measurements.
• Math is usually involved

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Metrics

• Metric system is much easier than the English
  systemthe conversion is always a factor of 10.

• Length is a 1-dimensional measure of distance.
• Metric system base unit is the meter, abbreviated
  m

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Metrics (cont.)

• Mass is a measure of the amount of matter in a
  substance.
• Metric system base unit is the kilogram,
  abbreviated kg

• Volume is a measure of the amount of space a
  substance takes up.
• Metric system base unit is the liter, abbreviated
  L.

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Weight

• Response of mass to the pull of gravity
• Weight changes when on different planets
• NOT THE SAME AS MASS!

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Metrics (cont.)

• Kilo hecto deka (m, g, L) deci centi
  milli
• k h dk or D d
  c m
• How do you remember the order of the prefixes?

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Metric Prefixes

• Kilo hecto deka (m, g, L) deci centi milli
• k h dk d
  c m
• 103 102 101 10-1
  10-2 10-3
• How do you remember the order of the prefixes?

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Practice Problem 2

• Make the following metric conversions
• 1. 875 cm _________ m.
• 2. 1.24 km _________ m.
• 3. 90,344 m _________ km.
• 4. 0.95 km _________cm.

9.75
1,240
90.344
950,000
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Accuracy and Precision

• Accuracy
• Close to the true or desired value
• Precision
• Reproducible measurements

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Measurement

• There is always an error in a measurement
• The human eye can read one decimal place beyond
  the accuracy of the instrument

• The measurement should be read as 8.0 /-0.1cm.

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Practice Problem 3
Read the volumes of the liquids below
9.02 mL
82 mL
62.0 mL
Container 1
Container 2
Container 3
65
10
150
60
9
100
55
8
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