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The Scientific Method •Mesurements •Units

Chemistry t1

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Page 1: Chemistry t1

The Scientific Method

•Mesurements•Units

Page 2: Chemistry t1

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

Page 3: Chemistry t1

The Functions of Science

pure science applied science

the search for knowledge; facts

using knowledgein a practical way

Page 4: Chemistry t1

Science attempts to establish cause-effect relationships.

Page 5: Chemistry t1

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.

Page 6: Chemistry t1

How does scientific knowledge advance?

1. curiosity2. good observations3. determination4. persistence

Page 7: Chemistry t1

The Scientific Method

Page 8: Chemistry t1

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

Page 9: Chemistry t1

Using the scientific method requires that one be a good observer.

observation inference

involves a judgmentor assumption

uses the fivesenses

Page 10: Chemistry t1

Parts of the Scientific Method

• Identify an unknown.• Make a hypothesis

(a testable prediction).• Experiment to test the hypothesis.• Draw a valid conclusion.

Page 11: Chemistry t1

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)

Page 12: Chemistry t1

DataObservations are also called data.

There are two types of data.

qualitative data quantitative data

descriptions; measurements; no numbers must have numbers

and UNITS

Page 13: Chemistry t1

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.

Page 14: Chemistry t1

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

Page 15: Chemistry t1

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.

Page 16: Chemistry t1

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

Page 17: Chemistry t1

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

Page 18: Chemistry t1

A physical quantity must include:A physical quantity must include:

NumberNumber + Unit+ Unit

Page 19: Chemistry t1

The Metric System

from

Indu

stry

Wee

k, 1

981

Nov

embe

r 30

Page 20: Chemistry t1

SI System

Map of the world where red represents countries which do not use the metric system

Page 21: Chemistry t1

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

Page 22: Chemistry t1

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

Page 23: Chemistry t1

The Official Standard Kilogram

The Official Standard Meter

Page 24: Chemistry t1

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

Page 25: Chemistry t1

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

Page 26: Chemistry t1

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

Page 27: Chemistry t1

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

Page 28: Chemistry t1

MEASUREMENT

Using Measurements

Page 29: Chemistry t1

Significant Figures

• Indicate precision of a measurement.

• Recording Sig Figs– Sig figs in a measurement include only the known

digits

2.3cm

Page 30: Chemistry t1

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

Page 31: Chemistry t1

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

Page 32: Chemistry t1

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

Page 33: Chemistry t1

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

Page 34: Chemistry t1

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

Page 35: Chemistry t1

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

Page 36: Chemistry t1

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

Page 37: Chemistry t1

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

Page 38: Chemistry t1

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:

Page 39: Chemistry t1

Conversion Factorsand

Unit Cancellation

Page 40: Chemistry t1

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”

Page 41: Chemistry t1

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(( ))

Page 42: Chemistry t1

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)

Page 43: Chemistry t1

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

Page 44: Chemistry t1

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

Page 45: Chemistry t1

How many kilometers is 15,000 decimeters?

X km = 15,000 dm = 1.5 km( )____1,000 m

1 km10 dm

1 m ( )______

Page 46: Chemistry t1

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…

Page 47: Chemistry t1

Simple Mathwith

Conversion Factors

Page 48: Chemistry t1

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

Page 49: Chemistry t1

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

Page 50: Chemistry t1

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( )_____

Page 51: Chemistry t1

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

Page 52: Chemistry t1

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

Page 53: Chemistry t1

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...

Page 54: Chemistry t1

Convert to mm3.

Page 55: Chemistry t1

Proportions: GRAPHICS

• Direct Proportion

Ø Inverse Proportion

xy

xy

1

y

x

y

x

Page 56: Chemistry t1

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

Page 57: Chemistry t1

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

Page 58: Chemistry t1

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.

Page 59: Chemistry t1

How to pick a lab partner

?