Honors Chem Aug 23

8/14/2019 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.

Honors Chem Aug 23

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