Upload
enpi275
View
418
Download
0
Tags:
Embed Size (px)
Citation preview
The Scientific Method
•Mesurements•Units
Natural ScienceNatural Science
Physical SciencePhysical Science Earth and Space ScienceEarth and Space Science Life ScienceLife Science
Physics Chemistry Geology Astronomy Botany Zoology
Meteorology
Oceanography
Ecology
Genetics
Natural science covers a very broad range of knowledge.
Wysession, Frank, Yancopoulos, Physical Science Concepts in Action, 2004, page 4
The Functions of Science
pure science applied science
the search for knowledge; facts
using knowledgein a practical way
Science attempts to establish cause-effect relationships.
Pure Science
The search for facts about the natural world.
?
- In science, we often try to establish a cause-effect relationship.
- Driven by curiosity: the need to know, explore, conquer something new.
How does scientific knowledge advance?
1. curiosity2. good observations3. determination4. persistence
The Scientific Method
Make observationMake observation
Ask questionAsk question
Develophypothesis
Develophypothesis
Test hypothesis with an
experiment
Test hypothesis with an
experiment
Analyze dataand draw
conclusions
Analyze dataand draw
conclusions
Hypothesis IS
supported
Hypothesis IS
supported
Hypothesis is NOT
supported
Hypothesis is NOT
supported
Developtheory
Developtheory
Test hypothesis with furtherexperiments
Test hypothesis with furtherexperiments
Revisehypothesis
Revisehypothesis
Scientific Method
Using the scientific method requires that one be a good observer.
observation inference
involves a judgmentor assumption
uses the fivesenses
Parts of the Scientific Method
• Identify an unknown.• Make a hypothesis
(a testable prediction).• Experiment to test the hypothesis.• Draw a valid conclusion.
The Skeptical Chemist
Robert Boyle
In “The Sceptical Chymist”
Boyle stated that scientific speculationscientific speculation was worthless unless it was supportedby experimental evidenceexperimental evidence.
This principle led to the development of the scientific methodscientific method.
(1661)
DataObservations are also called data.
There are two types of data.
qualitative data quantitative data
descriptions; measurements; no numbers must have numbers
and UNITS
Experiments
• Law of Nature – A verbal or mathematical description of a phenomenon that allows
for general predictions – Describes what happens and not why – Unlikely to change greatly over time unless a major
experimental error is discovered
P·V = P’·V’ Boyle’s Law of gases
• Theory – Attempts to explain why nature behaves as it does. – Is incomplete and imperfect, evolving with time to explain
new facts as they are discovered
Copyright 2007 Pearson Benjamin Cummings. All rights reserved.
Scientific Law vs. Scientific Theory
Law of GravityA theory tries to explain why
or how something happens.
A law states what happens.
Theory of Gravity
Atomic Theory
Collision Theory of Reactions
Scientific Method
• Observations• Hypothesis• Experimentation
– Controlled (one variable changed at a time)– Collect data (quantitative and qualitative)– Analyze data (graph, statistics…trends)
• Form valid conclusion.• After many experiments…form a theory.
Then
And
QuestionQuestion
ResearchResearch
HypothesisHypothesis
Procedure/Method
Procedure/Method
DataData
ObservationsObservations
ConclusionConclusion
What does the scientist wantto learn more about?
What does the scientist wantto learn more about?
Gathering of informationGathering of information
An “Educated” guess of ananswer to the question
An “Educated” guess of ananswer to the question
Written and carefullyfollowed step-by-step
experiment designed to testthe hypothesis
Written and carefullyfollowed step-by-step
experiment designed to testthe hypothesis
Information collected duringthe experiment
Information collected duringthe experiment
Written description of whatwas noticed during the
experiment
Written description of whatwas noticed during the
experiment
Was the hypothesis correct or incorrect?
Was the hypothesis correct or incorrect?
Next
Then
Next
And
Finally
First
Scientific MethodAn Overview
MeasurementsMeasurements
Metric (SI) unitsMetric (SI) units PrefixesPrefixes UncertaintyUncertainty
Significant figures
Significant figures
Conversionfactors
Conversionfactors
LengthLength
DensityDensity
MassMass VolumeVolume
Problem solving withconversion factors
Problem solving withconversion factors
Timberlake, Chemistry 7th Edition, page 40
A physical quantity must include:A physical quantity must include:
NumberNumber + Unit+ Unit
The Metric System
from
Indu
stry
Wee
k, 1
981
Nov
embe
r 30
SI System
Map of the world where red represents countries which do not use the metric system
The International System of Units
Length meter m
Mass kilogram kg
Time second s
Amount of substance mole mol
Thermodynamic temperatureKelvin K
Electric current amperes amps
Luminous intensity candela cd
Quantity Name Symbol
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 16
The Original Metric Reference (1790)
H2O= 1 liter
Volume
1 kg
H2O= 1 kilogram
Mass
1/10 m
1/10 m
1/10 m
= 1 meter
Length
1/10,000,000 Earth
The Official Standard Kilogram
The Official Standard Meter
Area and Volume: Derived Units
Area = length x width
= 5.0 m x 3.0 m
= 15 ( m x m)
= 15 m2
Volume = length x width x height
= 5.0 m x 3.0 m x 4.0 m
= 60 ( m x m x m)
= 60 m3
Derived Units Commonly Used in Chemistry
Area square meter m2
Volume cubic meter m3
Force newton N
Pressure pascal Pa
Energy joule J
Power watt W
Voltage volt V
Frequency hertz Hz
Electric charge coulomb C
Quantity Name Symbol
Prefixes in the SI System
Power of 10 for Prefix Symbol Meaning Scientific Notation_______________________________________________________________________
mega- M 1,000,000 106
kilo- k 1,000 103
deci- d 0.1 10-1
centi- c 0.01 10-2
milli- m 0.001 10-3
micro- m 0.000001 10-6
nano- n 0.000000001 10-9
The Commonly Used Prefixes in the SI System
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 118
Factor Name Symbol Factor Name Symbol
10-1 decimeter dm 101 decameter dam
10-2 centimeter cm 102 hectometer hm
10-3 millimeter mm 103 kilometer km
10-6 micrometer mm 106 megameter Mm
10-9 nanometer nm 109 gigameter Gm
10-12 picometer pm 1012 terameter Tm
10-15 femtometer fm 1015 petameter Pm
10-18 attometer am 1018 exameter Em
10-21 zeptometer zm 1021 zettameter Zm
10-24 yoctometer ym 1024 yottameter Ym
MEASUREMENT
Using Measurements
Significant Figures
• Indicate precision of a measurement.
• Recording Sig Figs– Sig figs in a measurement include only the known
digits
2.3cm
Significant Figures
• Counting Sig Figs (Table 2-5, p.47)
– Count all numbers EXCEPT:
• Leading zeros – 0,0025
• Trailing zeros without a decimal point -- 2500
4. 0,080
3. 5280
2. 402
1. 23.50
Significant Figures
Counting Sig Fig Examples
1. 23,50
2. 402
3. 5280
4. 0,080
4 sig figs
3 sig figs
3 sig figs
2 sig figs
Significant Figures
• Calculating with Sig Figs– Multiply/Divide - The # with the fewest sig figs
determines the # of sig figs in the answer.
(13,91g/cm3)(23,3cm3) = 324,103g
324 g
4 SF 3 SF3 SF
Significant Figures
• Calculating with Sig Figs (con’t)– Add/Subtract - The # with the lowest decimal value
determines the place of the last sig fig in the answer.
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g 7,9 mL 350 g
3.75 mL
+ 4.1 mL
7,85 mL
224 g
+ 130 g
354 g
Significant Figures
• Calculating with Sig Figs (con’t)– Exact Numbers do not limit the # of sig figs in the answer.
• Counting numbers: 12 students• Exact conversions: 1 m = 100 cm• “1” in any conversion: 1 in = 2,54 cm
Significant Figures
5. (15,30 g) ÷ (6,4 mL)
Practice Problems
= 2,390625 g/mL
18.1 g
6. 18,9 g
- 0,84 g18.06 g
4 SF 2 SF
2,4 g/mL2 SF
Scientific Notation
• Converting into scientific notation:
– Move decimal until there’s 1 digit to its left. Places moved = exponent.
– Large # (>1) positive exponentSmall # (<1) negative exponent
– Only include sig. figs.
65000 kg 6.5 × 104 kg
Scientific Notation
7. 2,400,000 g
8. 0.00256 kg
9. 7 10-5 km
10. 6.2 104 mm
Practice Problems
2.4 106 g
2.56 10-3 kg
0.00007 km
62,000 mm
Scientific Notation
• Calculating with scientific notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
5.44EXPEXP
EEEE÷÷
EXPEXP
EEEE ENTERENTER
EXEEXE7 8.1 4
= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol
Type on your calculator:
Conversion Factorsand
Unit Cancellation
Unit ConversionUnit Conversion
1 minute = 60 seconds1 minute = 60 seconds
1 minute 1 minute
60 seconds60 seconds= 1= 1
1 minute 1 minute
60 seconds60 seconds= 1= 1
“Conversion factors”“Conversion factors”
Calculation Corner: Unit ConversionCalculation Corner: Unit Conversion
1 min1 min
60 s60 s
60 s60 s
1 min1 min
“Conversion factors”“Conversion factors”
= 180 s= 180 s60 s60 s
1 min1 min(( ))3 min3 min(( ))
How many cm are in 1.32 meters?
applicable conversion factors:
equality:
or
X cm = 1.32 m =
1 m = 100 cm
______1 m100 cm
We use the idea of unit cancellation
to decide upon which one of the two
conversion factors we choose.
______1 m
100 cm
( )______1 m
100 cm 132 cm
(or 0.01 m = 1 cm)
How many meters is 8.72 cm?
applicable conversion factors:
equality:
or
X m = 8.72 cm =
1 m = 100 cm
______1 m100 cm
Again, the units must cancel.
______1 m
100 cm
( )______ 0.0872 m1 m100 cm
How many feet is 39.37 inches?
applicable conversion factors:
equality:
or
X ft = 39.37 in =
1 ft = 12 in
______1 ft 12 in
Again, the units must cancel.
( )____ 3.28 ft1 ft12 in
______1 ft
12 in
How many kilometers is 15,000 decimeters?
X km = 15,000 dm = 1.5 km( )____1,000 m
1 km10 dm
1 m ( )______
How many seconds is 4.38 days?
=
1 h60 min24 h
1 d 1 min60 s____( ) ( )____( )_____X s = 4.38 d
378,432 s
3.78 x 105 sIf we are accounting for significant figures, we would change this to…
Simple Mathwith
Conversion Factors
Measured dimensions of a rectangle:
Find area of rectangle.
A = L . W
= (9.70 cm)(4.25 cm)
length (L) = 9.70 cm
width (W) = 4.25 cm
L
W=
Example Problem
41.2 cm2 . cm
Convert 41.2 cm2 to m2.
100 cm1 m( )______
X m2 = 41.2 cm2
X m2 = 41.2 cm.cm
Recall that… 41.2 cm2 = 41.2 cm.cm
100 cm1 m( )______
X m2 = 41.2 cm2 = 0.412 m2
= 0.412 cm.m
WRONG!
( )______100 cm
1 m
= 0.00412 m2
( )______100 cm
1 m 2 = 0.00412 m2
Convert 41.2 cm2 to mm2.
X mm2 = 41.2 cm2
X mm2 = 41.2 cm.cm
Recall that… 41.2 cm2 = 41.2 cm.cm
1 cm
10 mm( )_____
= 4,120 mm2
=
1 cm
10 mm( )_____
4,120 mm2
1 cm
10 mm 2( )_____
Measured dimensions of a rectangular solid:
Find volume of solid.L
W
H
Length = 15.2 cm
Width = 3.7 cm
Height = 8.6 cm
V = L . W . H
= (15.2 cm)(3.7 cm)(8.6 cm)
= 480 cm3
Convert to m3.
X m3 = 480 cm3 = 0.000480 m3
100 cm
1 m 3
( )_____
X m3 = 480 cm3 =
X m3 = 480
100 cm
1 m( )_____100 cm
1 m( )_____100 cm
1 m( )_____ =
or
cm.cm.cm
1 m1000000 cm( )_________
3
34.80 x 10-4 m3
or
32cm
Measured dimensions of a rectangular solid:
Find volume of solid.L
W
H
Length = 15.2 cm
Width = 3.7 cm
Height = 8.6 cm
V = L . W . H
= (0.152 m)(0.037 m)(0.086 m)
= 0.000480 m3
0.152 m0.037 m
0.086 m
Convert to m3...
Convert to mm3.
Proportions: GRAPHICS
• Direct Proportion
Ø Inverse Proportion
xy
xy
1
y
x
y
x
Rules for Counting Significant Figures
1. Nonzero integers always count as significant figures.
2. Zeros: There are three classes of zeroes.
a. Leading zeroes precede all the nonzero digits and DO NOT count assignificant figures. Example: 0.0025 has ____ significant figures.
b. Captive zeroes are zeroes between nonzero numbers. These alwayscount as significant figures. Example: 1.008 has ____ significant figures.
c. Trailing zeroes are zeroes at the right end of the number.
Trailing zeroes are only significant if the number contains a decimal point.Example: 1.00 x 102 has ____ significant figures.
Trailing zeroes are not significant if the number does not contain a decimalpoint. Example: 100 has ____ significant figure.
3. Exact numbers, which can arise from counting or definitions such as 1 in = 2.54 cm, never limit the number of significant figures in a calculation.
2
4
3
1
Significant figures: Rules for zeros
Leading zeros are not significant.
Captive zeros are significant.
Trailing zeros are significant.
Leading zeroLeading zero
Captive zeroCaptive zero
Trailing zeroTrailing zero
0.421
4012
114.20
– three significant figures
– four significant figures
– five significant figures
Significant Figures
Number ofQuantity Certain Digits Significant
Figures
14.379 g 1 4 3 7 9 9 (thousandths) 5
6.02 mL 6 0 2 2 (hundredths) 3
120.580 m 1 2 0 5 8 0 0 (thousandths) 6
7.5 g 7 5 5 (tenths) 2
0.037 g 3 7 7 (thousandths) 2
0.0370 g 3 7 0 0 (ten-thousandths) 3
*The position of the decimal point has nothing to do with the number of significant figures.
How to pick a lab partner
?