unit 1 scientific method + measurement chem 1 fall 07
TRANSCRIPT
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Unit 1Scientific Method
+Measurement
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
Ivan Pavlov observed dogs salivating and
hypothesized that a sound would cause
dogs to salivate.
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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 1400°C 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.
• There’s 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 system…the 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
65
60
55
10
9
8
150
100
50
Container #1 Container #2 Container #39.02 mL 82 mL 62.0 mL
Read the volumes of the liquids below