honors chem aug 23
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Chapter 1: Measurement
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PrefixPrefix SymbolSymbol UnitUnit ScientificScientificmega- M 1,000,000.0 10^6
kilo- k 1,000.0 10^3
hecto- h 100.0 10^2
deka- da 10.0 10^1
meter (base) m 1.0 10^0
deci- d 0.1 10^-1
centi- c 0.01 10^-2
milli- m 0.001 10^-3
micro- 0.000001 10^-6
Prefixes used in the metric systemPrefixes used in the metric system
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Metric Conversions using Dimensional
Analysis
The key to using dimensional analysis is the
correct use ofconversion factorsconversion factors
What is a conversion factor?What is a conversion factor?
A conversion factor is a fraction whoseA conversion factor is a fraction whose
numerator and denominator are the samenumerator and denominator are the same
quantity expressed in different unitsquantity expressed in different units
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Example of a conversion factor:
Inches to centimeters
2.45
1.0
cm
in
1.0
2.45
in
cm
Both the numerator and the denominator
are expressing the same quantity of lengthusing different units
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When using conversion factors, we want the
given units to cancel
Then we end up with the desired units
DesiredGiven Desired
Given
Unit
Example: Using conversion factors, convert6.25 inches to centimeters
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Step 1: Use our inches-to-centimeters
conversion factor
Question: Which one do we use?
1.0
2.54
in
cmor
2.54
1.0
cm
in
?
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Answer: We want the desired unit in the
numerator of the conversion factor
Step 2: Set up the calculation like this
2.546.25 15.875
1.0
cmin cmin
The inch units cancel, and we are left with
centimeters, our desired unit
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Lets use conversion factors to express 2.6
meters as millimeters:
Here are the conversion factors we need:
10
1
dm
m
10
1
cm
dm
10
1
mm
cm
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1 1 12.6 0.0026
10 10 10
cm dm mmm m
mm cm dm
10 10 102.6 26001 11
dm cm mmm mmm cmdm
Always set up your calculations so that given
units cancel, and you get the desired units at
the end
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Scientific Method
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Science is a process of inquiry that includes
repeatable observations and testable
hypotheses
This process blends two main types of
reasoning: InductiveInductive reasoningreasoningandhypothetico-deductivehypothetico-deductive reasoningreasoning
Most scientists practice a combination ofboth
The wordsciencescience is derived from a Latin verb
meaning to knowto know
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Science and InductionScience and Induction
Scientific investigation can lead to importantScientific investigation can lead to importantconclusions based on a type of logic calledconclusions based on a type of logic called
inductive reasoninginductive reasoning
An inductive conclusion is a generalizationAn inductive conclusion is a generalization
that summarizes many concurrentthat summarizes many concurrent
observationsobservations
ObservationObservation General PrincipleGeneral Principle
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Example: All the swans at Lake Mead areExample: All the swans at Lake Mead are
white in colorwhite in color
All the swans at Lake Powell are white inAll the swans at Lake Powell are white in
colorcolor
All the swans at Lake Michigan are white inAll the swans at Lake Michigan are white incolorcolor
All the swans at Lake Okeechobee are whiteAll the swans at Lake Okeechobee are white
in colorin color
Argument: Therefore, all swans are whiteArgument: Therefore, all swans are white
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This is inductive reasoning: The argument thatThis is inductive reasoning: The argument that
all swans are white is a generalization madeall swans are white is a generalization made
from many specific observationsfrom many specific observations
There is a big problem with this argument:There is a big problem with this argument:
What is it?What is it?
ObservationObservation General PrincipleGeneral Principle
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If someone finds a black swan at another lake
somewhere, our argument, or theory, is no
longer valid
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Hypothetico-Deductive ScienceHypothetico-Deductive Science
Hypothetico = hypothesis-generatingHypothetico = hypothesis-generating
Deduction = Another form of logicDeduction = Another form of logic
Deductive logicDeductive logicdiffers from inductive logicdiffers from inductive logic
When using deductive logic, we go from theWhen using deductive logic, we go from the
generalgeneralto theto the specificspecific
Recall: A hypothesis is a tentative answer tosome question
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Deductive logic differs from inductive logicDeductive logic differs from inductive logic
When using deductive logic, we go fromWhen using deductive logic, we go fromgeneralgeneralpremisespremises toto specificspecificconclusionsconclusions
Who is this guy?
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This is Socrates, and well use him in anThis is Socrates, and well use him in an
example of deductive logicexample of deductive logic
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All men are mortalAll men are mortal
Socrates is a manSocrates is a manTherefore, Socrates is mortalTherefore, Socrates is mortal
OrOr
All organisms are composed of tiny cellsAll organisms are composed of tiny cells
Socrates is an organismSocrates is an organism
Therefore, Socrates is composed of tiny cellsTherefore, Socrates is composed of tiny cells
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In the process of science, the deduction usually
takes the form of predictions about what the
outcomes of our experiments or observations
should be
We then test the hypothesis by performing an
experiment to see whether or not the resultsare as predicted
General Premises Specific
Conclusion
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As a formal process of inquiry, the
scientific method consists of a
series of steps.
Most science is far less structured
than presented here.
The key element here is the
use of hypothetico-deductive reasoning.
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My flashlight doesnt work
Whats wrong with myflashlight?
The batteries are dead
If I my hypothesis iscorrect
and I replace theand I replace the
batteriesbatteries
Hypothetico-DeductiveHypothetico-Deductive
ReasoningReasoning
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ThenThen::
My flashlight should work!My flashlight should work!
But what if my flashlight still doesnt work?But what if my flashlight still doesnt work?
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We can always generate alternativeWe can always generate alternative
hypotheses and test them in the samehypotheses and test them in the same
mannermanner
Alternative hypothesesAlternative hypotheses::
The bulb is burned outThe bulb is burned out
The contacts are corrodedThe contacts are corroded
The on-off switch is brokenThe on-off switch is broken
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The point here is that any one of theseThe point here is that any one of these
hypotheses can be tested according to thehypotheses can be tested according to the
scientific methodscientific methodIt is also important to note that all theseIt is also important to note that all these
hypotheses are falsifiable under the scientifichypotheses are falsifiable under the scientific
methodmethod
Remember our theory about the swans:Remember our theory about the swans:
according to the scientific method we look foraccording to the scientific method we look for
evidence that disproves our theoryevidence that disproves our theory
One black swan can disprove our theory thatOne black swan can disprove our theory that
all swans are whiteall swans are white
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ExperimentsExperiments
In order to test a hypothesis we must design aIn order to test a hypothesis we must design a
suitable experimentsuitable experiment
When performing our experiment, we mustWhen performing our experiment, we mustlook for results relating to our hypothesislook for results relating to our hypothesis
These results will either support or not supportThese results will either support or not support
our hypothesisour hypothesis
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I want to conduct an experiment to identifyI want to conduct an experiment to identify
essential nutrients required in plantsessential nutrients required in plants
I will use plants grown hydroponically (in waterI will use plants grown hydroponically (in water
rather than soil)rather than soil)
One group of plants will grow in an aqueousOne group of plants will grow in an aqueous
solution ofsolution ofcomplete nutrientscomplete nutrients
Another group of plants will grow in a solutionAnother group of plants will grow in a solution
lacking one nutrientlacking one nutrient
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Hydroponic Farming
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Our plants growing in a complete nutrientOur plants growing in a complete nutrient
solution is called thesolution is called the controlcontrol groupgroup
Our plants growing in a solution missing oneOur plants growing in a solution missing one
nutrient is called thenutrient is called the experimentalexperimental groupgroup
The control group allows us to compare withThe control group allows us to compare with
the experimental groupthe experimental group
If the missing nutrient has an effect on theIf the missing nutrient has an effect on the
experimental plants, their appearance shouldexperimental plants, their appearance should
be different than the control group plantsbe different than the control group plants
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What about the variables?What about the variables?
For our experiment to succeed, we mustFor our experiment to succeed, we mustidentify all of the variablesidentify all of the variables
One variable is theOne variable is the growth responsegrowth response of theof theplants in the incomplete nutrient solutionplants in the incomplete nutrient solution
Another variable is theAnother variable is the difference in thedifference in the
experimental nutrient solutionexperimental nutrient solution
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The incomplete nutrient solution is the variableThe incomplete nutrient solution is the variable
that we, as investigators, arethat we, as investigators, are manipulatingmanipulating
We call this variable theWe call this variable the independentindependent variablevariable
We willWe willmeasuremeasure the effect of the independentthe effect of the independentvariable on the growth of the plantsvariable on the growth of the plants
The response of the plants to the alteredThe response of the plants to the alterednutrient solution is called thenutrient solution is called the dependentdependent
variablevariable
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We call the response of the plants theWe call the response of the plants the
dependent variabledependent variable because the magnitude ofbecause the magnitude of
the response depends on how wethe response depends on how wemanipulate themanipulate the independent variableindependent variable
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Homework: Due Next Class
Worksheet on using dimensional analysis
Prepare your hypothesis for you science fair
projects.
Study for test next class:
Check homework page on Friday for study
guide.
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