Scientific & Chemical Fundamentals

Dr. Ron Rusay

Spring 2008

© Copyright 2003-2008 R.J. Rusay© Copyright 2003-2008 R.J. Rusay

Scientific & Chemical Fundamentals

Chemistry & the Scientific Method Matter : Classification & Properties Mathematics / Arithmetic:

Exponents, Significant Figures

Measurement & Units: (SI & metric) Conversions and Relationships:

Dimensional Analysis: Density, Percent VOCABULARY: Key Terms, Bold Style Learning

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© Copyright 1998-2008 R.J. Rusay

Textbook Reading

Chemical Foundations

1.1 Chemistry: An Overview1.2 The Scientific Method1.3 Units of Measurement1.4 Uncertainty in Measurement1.5 Significant Figures and Calculations1.6 Dimensional Analysis1.7 Temperature1.8 Density1.9 Classification of Matter

Science & The Science & The Scientific Method Scientific Method

Law vs. Theory

QUESTIONThe difference between a scientific law and a scientific theory can, at times, be confusing. For example, we will refer to the “Atomic theory” or perhaps the “Law of Gravity.” Should the Law of Gravity be changed to the Theory of Gravity?

1. Yes, no one can see gravity, it is better described as a theory.2. No, scientific laws are based on summaries of many

observations and gravity observations are well known andpredictable.

3. Yes, gravity is better described as a theory because gravity explains why masses attract each other and theories are about explaining observations.

4. No, keep it as a law, laws offer explanations and gravity explains why masses attract each other and laws are about explaining observations.

ANSWERChoice 2 follows the agreed-upon distinction between a theory and a law. Observations that consistently agree and provide the same result in a variety of systems become “Laws.” Theories are attempts to offer human interpretations and explanations about what was observed. Therefore, we should continue calling the summary about attractions the Law of Gravitation.

Section 1.2: The Scientific Method

Some Possible Steps in the Scientific Method

1.1. ObservationsObservations• qualitativequalitative• quantitativequantitative

2.2. Formulating hypothesesFormulating hypotheses• possible explanation(s) for the possible explanation(s) for the

observationobservation 3.3. Performing experimentsPerforming experiments

• gathering new informationgathering new information• testing whether the hypotheses are testing whether the hypotheses are

validvalid 4.4. Developing a theoryDeveloping a theory 5.5. Testing & RefiningTesting & Refining

Chemistry: The Study of Matter In all of its forms & all of its behaviors Sub-categories (not so distinct any longer)

• Organic: carbon• Inorganic: non-carbon• Organometallic: organic + inorganic• Analytical: what?, how much?, how pure?• Biological / Biochemistry: living organisms• Physical: energy, changes, rates• Nuclear: the nucleus• Environmental: interdisciplinary, eg. Oceanography

© Copyright 1998-2008 R.J. Rusay

Chemistry & Matter (Chemicals)

How many different chemicals do you think have been reported in the scientific literature?

A) 100,000B) 1,000,000C) 10,000,000D) 100,000,000E) 1,000,000,000

CAS Registry : ~12,000 in 1907; > 31 million June 2007CAS Registry : ~12,000 in 1907; > 31 million June 2007

Today ~ 500 new molecules are added / hrToday ~ 500 new molecules are added / hr

Chemistry & Matter:Properties & States

• Physical vs. Chemical Properties

• Solid (s), Liquid (l), Gas (g)

• Homogeneous vs. Heterogeneous Mixtures

• Organization of atoms/molecules:

atoms/elements molecules/compounds

• Extensive vs. Intensive PropertiesVaries with amount (extensive) or does not vary

with amount (intensive)

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Observations of Physical & Chemical Properties

QuickTime™ and aCinepak decompressor

are needed to see this picture.

States of Matter

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Organization of Matter01_15

Heterogeneousmixtures

Physicalmethods Homogeneous

mixtures (solutions)

Atoms

Compounds Elements

Nucleus Electrons

Pure substances

Protons Neutrons

Quarks Quarks

Matter

Physicalmethods

Chemicalmethods

leptonsleptons

Up,down, strange, charm, bottom, topUp,down, strange, charm, bottom, top

Classification Classification of Matterof Matter

Organization of Matter01_15

Heterogeneousmixtures

Physicalmethods Homogeneous

mixtures (solutions)

Atoms

Compounds Elements

Nucleus Electrons

Pure substances

Protons Neutrons

Quarks Quarks

Matter

Physicalmethods

Chemicalmethods

leptonsleptons

up,down, strange, charm, bottom, topup,down, strange, charm, bottom, top

muons, tau, muons, tau, neutrinosneutrinos

Classification Classification of Matterof Matter

Using Physical & Chemical Properties: Distinguishing a Compound & a Mixture

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

The effects of a The effects of a magnet on iron: filings magnet on iron: filings in a mixture and atoms in a mixture and atoms in a molecule. in a molecule.

Types of Mixtures

Mixtures have variable composition of two or Mixtures have variable composition of two or more components.more components.

AA homogeneous mixture homogeneous mixture is a solution (for is a solution (for example, vinegar: water + acetic acid, or steel & example, vinegar: water + acetic acid, or steel & bronze: solid metals)bronze: solid metals)

AA heterogeneous mixture heterogeneous mixture is, to the naked is, to the naked eye, clearly not uniform (for example, a bottle of eye, clearly not uniform (for example, a bottle of ranch dressing with two layers: water + oil, or two ranch dressing with two layers: water + oil, or two solids: iron and sulfur)solids: iron and sulfur)

Element:Element: A substance that cannot be A substance that cannot be broken into simpler substances by broken into simpler substances by chemical means, eg. Fe, Iron or Schemical means, eg. Fe, Iron or S8 8 SulfurSulfur

Compound:Compound: A substance with a A substance with a constant composition that can be constant composition that can be broken down into elements only by broken down into elements only by chemical processes,eg. FeS, Iron chemical processes,eg. FeS, Iron (II) sulfide(II) sulfide

Elements & Compounds

QUESTIONIs a cup of coffee a homogeneous solution or a compound? Which of the following agrees with your reasoning?

1. The coffee in the cup is a homogeneous solution because it contains the same components throughout, but there are many compounds dissolved to make coffee.

2. The coffee in the cup is a compound because it has a setratio of components that make it the same throughout.

3. The coffee in the cup is both a compound and a solution.It looks the same throughout like a true solution, yet it alwayshas the same amount of each component.

4. The coffee in the cup is a heterogeneous solution not homogeneous because it contains distinct, differentcompounds dissolved to make coffee.

ANSWERChoice 1 provides the best reasoning. The coffee in the cup is a homogeneous mixture of components, making it a solution. The amount of each component can vary greatly from coffee bean to coffee bean. Compounds do not have a variable composition like solutions.

Section 1.9: Classification of Matter

Measurement & Units(SI units & common units in General Chemistry)

•Quantitative vs. Qualitative

• MASS (Chem: gram; SI: kg)

• LENGTH (Chem: cm & others; SI: m)

• TEMPERATURE (Celsius & Kelvin; SI: K)

• VOLUME (Chem: mL; SI: Liter)

• CHEMICAL AMOUNT: Mole (mol)

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Units U.S. SI Chemistry

Mass (weight) Pound (lb) Kilogram (kg) “Gram”(g, mg)

Volume Gallon (gal) Liter (L) “Liter” (mL, L)

Temperature Fahrenheit(oF)

Kelvin (K) K & Celsius (oC)

Length Mile (mi),Feet(ft), Inches

(in)

Meter (m) “Meter” (cm, mm, nm)

Time Second (s) Second (s)Mole (mol)

Units of Measure

u

Mass and Volume Mass and Volume MeasurementMeasurement

Mass Determination(Weighing Devices: Balances)

Volumes of regular shapes

hh

V = l x w x hV = l x w x h

V = s V = s 33

Volume

01_05

1dm3= 1 L

1 cm

1 cm

1m3

1cm3= 1 mL

Liquid Measurement Tools

Numbers & MeasurementThe Importance of Units

Measurement - quantitative observation consisting of 2 partsMeasurement - quantitative observation consisting of 2 parts

• Part 1 - Part 1 - numbernumber• Part 2 - Part 2 - unitunit

Examples:Examples:• 2020 gramsgrams• 6.63 6.63 joules / secondjoules / second

Scale: Size & Comparison

Macroscopic vs. Microscopic IBM financed Video: http://www.wordwizz.com/imagendx.htm

How would you compare your lifespan?.. to that of a dog? ….to the age of the earth?…How about the age of mankind to that of all life?.. ..the age of industrialized mankind to the age of mankind?

Graphic Comparisons

Powers of Ten:Scale

Shorthand PrefixesLanguage describes scale (prefixes)

How many zeroes does yotta yotta yotta have? How many zeroes does yotta yotta yotta have?

Commonly used prefixes in Chemistry

These should be known from memory.These should be known from memory.

Commonly used prefixes in Chemistry

Attosecond spectroscopy = 10Attosecond spectroscopy = 10 -15 -15 x 10 x 10 -3 -3 secondssecondsScience, Science, 317317, 765-775, (2007), 765-775, (2007)

““The Electron Stopwatch”The Electron Stopwatch”

QUESTIONConveniently, a U.S. nickel has a mass of approximately 5 grams. If you had one dollar’s worth of nickels what would be the mass of the nickels in milligrams?

1. 100 milligrams2. 50 milligrams3. 1,000 milligrams4. 100,000 milligrams

1000 milligrams (mg) = 1 gram (g)1000 milligrams (mg) = 1 gram (g)

ANSWERChoice 4 shows the correct conversion. After determining that 20 nickels make up one dollar, then one dollar’s worth of nickels would have a mass of 100 grams. Next, the conversion between grams and milligrams can be performed by multiplying by 1,000 (because there are 1,000 milligrams per gram.)

Section 1.3: Units of Measurement

Scientific Notation &Significant Digits

Scientific Notation: A single digit followed by a Scientific Notation: A single digit followed by a decimal and a power of ten.decimal and a power of ten.

Examples: 2,345 mL and 0.002340 g Examples: 2,345 mL and 0.002340 g

2,345 mL = 2,345 mL = 2.345 x 10 2.345 x 10 33mLmL 0.002340 g = 0.002340 g = 2.3402.340 x 10x 10 -3 -3 g g

Numbers

• Expressing a number correctly is determined by the method used in the measurement!

• How many numbers should I include? Significant Digits (Figures)

Consider: the exactness of the measured value

• Short Hand expression translates the number: Scientific Notation

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What is the length of the rod?

Different measurement tools give different numbers:Different measurement tools give different numbers:Which ruler is better?Which ruler is better?

? cm? cm

? cm? cm

4.2 - 4.3cm4.2 - 4.3cm

4.24 - 4.25cm4.24 - 4.25cm

What is the diameter of a circle?All measuring devices are not the same, and the values All measuring devices are not the same, and the values

(numbers) that come from them indicate their (numbers) that come from them indicate their limitations.limitations.

Is there a better instrument to use other than a ruler? Is there a better instrument to use other than a ruler?

01_08

0

10

20

30

40

50

mL

Buret

22.2 mL

What does each line represent? What does each line represent?

1 mL1 mL

What can be estimated? What can be estimated?

O.O.1 1 mLmL

Measurement Assignmenthttp://chemconnections.llnl.gov/General/Chem120/volume1.htm

Temperature ScalesRelative to Water

“Normal” Body Temperature

QUESTIONDr. R. walks into class and claims, “It is very cold in here today. It feels like 242 K.” If that were the temperature, would you agree that you would feel cold? What would that be in Celsius degrees?

1. I agree, that would be 31°C.2. I agree, that would be – 31°C.3. I do not agree, that would be 31°C.4. I agree, that would be –31.15°C.

ANSWERChoice 2 provides a correct (very) cold temperature. The formula to use is K = °C + 273.15. However this must be rearranged slightly to yield K – 273.15 = °C. Since this is a subtraction, the correct value would have no numbers beyond the decimal point because 242 does not have numbers beyond the decimal point.

Section 1.7: Temperature

Temperature

01_09

(c)(b)(a)

Precision & Accuracy

QUESTIONS: 1) Rank the images from best to worst precision.1) Rank the images from best to worst precision.

2) Rank the images from best to worst accuracy. 2) Rank the images from best to worst accuracy. c > b > ac > b > a

c > a > bc > a > b

QUESTIONTwo Chem 120 students are each drinking a soft drink after class. The volumes of both containers are respectively listed as 375 milliliters. Philip remarks that the law requires bottlers to be very precise. Susan correctly responded:

1. If precision were the only requirement, bottlers could claim any volume as long as it was always very nearly thesame volume.

2. Since precision is a requirement, bottlers have to get exactly 375 mL in every can.

3. Bottlers must have a precise average of all of the containers in a case of soft drinks equal to 375 mL.

4. If there were a difference of no more than +/- 1 mL between containers, the bottlers can sell their beverage.

ANSWERChoice 1 best fits what scientists define as precise. High precision measurements may have closeness to a set goal (such as 375 mL in a can) but precision always means closeness within a set of measurements. If the volumes of 100 containers were within a range of 294 to 295 mL the volumes would be precise, but not accurately 375 mL.

Section 1.4: Uncertainty in Measurement

Precision & AccuracyNumerical Data

a) b) c)

9.52 8.40 7.958.36 8.35 8.007.29 8.42 8.058.34 8.36 7.95

__________ __________ __________Average

a) b) c)

9.52 8.40 7.958.36 8.35 8.007.29 8.42 8.058.34 8.36 7.95

__________ __________ __________Average 8.378 8.383 7.988

Round Off 8.38 8.38 7.99

a) b) c)deviation deviation deviation

9.52 -1.14 8.40 -0.02 7.958.36 0.02 8.35 0.03 8.007.29 1.09 8.42 -0.04 8.058.34 0.04 8.36 0.02 7.95

__________ __________ __________Average 8.378 0.573 8.383 0.028 7.988

Round Off 8.38 +/- 0.57 8.38 +/- 0.03 7.99

Absolute value ( all of the - become +)

0.04-0.01-0.060.04

0.038

+/- 0.04

QUESTION

A)A) Precision: a > c > bPrecision: a > c > b B) Precision: b > c > aB) Precision: b > c > a

C) Precision: a = b > cC) Precision: a = b > c D) Precision: a > b > cD) Precision: a > b > c

Average Average Average

a) b) c)

8.38 8.38 7.99

average average average

deviation deviation deviation

a) b) c)

+/- 0.57 +/- 0.03 +/- 0.04

Rank the relative precision of the three sets of data: Rank the relative precision of the three sets of data: a), b) and c).The accepted value is 8.08.a), b) and c).The accepted value is 8.08.

Answer:Answer:

QUESTION

A)A) Accuracy: a > c > bAccuracy: a > c > b B) Accuracy: b > c > aB) Accuracy: b > c > a

C)C) Accuracy: c > a = b Accuracy: c > a = b D) Accuracy: a = b > cD) Accuracy: a = b > c

Average Average Average

a) b) c)

8.38 8.38 7.99

average average average

deviation deviation deviation

a) b) c)

+/- 0.57 +/- 0.03 +/- 0.04

Rank the relative accuracy of the three sets of data: Rank the relative accuracy of the three sets of data: a), b) and c).The accepted value is 8.08.a), b) and c).The accepted value is 8.08.

Answer:Answer:

Reporting NumbersRules for Significant Digits (Figures)

Nonzero integersNonzero integers always count always count as significant figures.as significant figures.

3456 g3456 g has how many sig figs? has how many sig figs? 44 sig figs. sig figs.

• Expressed in scientific notation?Expressed in scientific notation?

3.456 x 10 3.456 x 10 33 g g

Reporting NumbersRules for Significant (Digits) Figures

Exact numbers (unit, conversion or Exact numbers (unit, conversion or scale factors)scale factors) can can have an infinite have an infinite number of significant figures.number of significant figures.

11 liter = liter = 1,000.1,000. ml, exactlyml, exactly

11 inch = inch = 2.542.54 cm, exactlycm, exactly

Systematic Problem SolvingDimensional/Unit Analysis

How many mL of milk are in a1/2 gallon carton?How many mL of milk are in a1/2 gallon carton?

? mL? mL0.500.50 gal gal

11 gal = gal = 44 qt qt 11 qt = qt = 946946 mL mL

0.500.50 gal gal | | 11 qt qt || 946946 mL mL | | 44 gal gal | | 11 qtqt

= ? mL= ? mL

Complete the followingUnits & Conversions

13,000,000,000 yrs. ________________ __? gigayears 13 Gyrs

NumberNumber Scientific Notation Scientific Notation Named unit Named unit 1.3 x 1010 yrs

___________ mL ___________ mL ______________ mL ______________ mL 0.546 Liters0.546 Liters

____________ kg____________ kg ____8.45 x 10 8.45 x 10 -1-1 kg kg___ ____ _? grams? grams____

5.46 X 10 5.46 X 10 22 546 546

0.8450.845

845845 g g

0.546 L0.546 L

ZerosZeros

Leading zerosLeading zeros do not count as do not count as significant figures.significant figures.

0.0486 mL0.0486 mL has how many sig figs? has how many sig figs? 33 sig figs. sig figs.

• Number expressed in scientific Number expressed in scientific notation?notation? 4.86 x 10 4.86 x 10 -2 -2 mLmL

ZerosZeros

Captive zeros Captive zeros always count asalways count assignificant figures.significant figures.

16.16.007 cm 7 cm has how many sig figs?has how many sig figs? 44 sig figs. sig figs.

Number expressed in scientific Number expressed in scientific notation?notation? 1.607 x 10 1.607 x 10 11 cm cm

ZerosZeros

Trailing zerosTrailing zeros are significant onlyare significant only if if the number contains a decimal the number contains a decimal point.point.

9.300 kg9.300 kg has how many sig figs? has how many sig figs? 44 sig figs. sig figs.

• Number expressed in scientific Number expressed in scientific notation?notation? 9.3009.300 kgkg

QUESTIONWhich one of the following does NOT represent a result with four significant digits?

1. 0.071002. 0.71003. 0.70104. 0.0710

ANSWERChoice 4 only has three significant digits. Note that the lone zero in front of the decimal point is not based on any measurement and the next zero serves only as a place holder not as a measurement.

Section 1.5: Significant Figures and Calculations

Mathematics & Arithmetic

• Relative to method(s) of measurement

• Short Hand expression: Scientific Notation

• Numbers : How many to include?

Quantitative vs. Qualitative

• Addition/Subtraction......

• Multiplication/Division.....

• What is “significant”?.....Rounding Off

• http:dbhs.wvusd.k12.ca.us/SigFigsFable.html

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Computational Rules

• Addition/Subtraction: Answer expressed to the least number of decimal places of the figures in the process

• Multiplication/Division: Answer expressed to the least number of significant figures

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Addition

Four students were each asked to measure a piece of wire and provide a total length for the four pieces.

Report the result correctly:0.05 cm

12.01 cm1.9 cm

+ 2.386 cm_______

16.346 cm16.346 cm

QUESTIONIf you were unloading a 23.50 kg box of books from your car and a “friend” added two more 482 gram chemistry books, how much in kg and using the rules for significant digits, would you be lifting?

1. 23.98 kg2. 24.464 kg3. 24.46 kg4. 24.5 kg

ANSWERChoice 3 provides both the conversion and proper number of significant digits. Consider that the 482 grams of mass must be doubled (to include both books) and that 482 grams is 0.482 kg. When adding two measurements always report your answer to the same number of decimal places as the least precise measurement used in the calculation. In this case the answer should be reported to the hundredths place.

Section 1.5: Significant Figures and Calculations

Mathematical Processes:

Provide correct answers assuming each value (unit omitted) is written with the correct number of sig figs:

12.01 x 1.90_______ _______ _______=

2.386

12.01 x 1.90_______ _______ _______+ 0.05 =

2.386

9.56370 9.56370

9.613709.61370

QUESTIONThe average mass of a certain brand of vitamin C tablets is 253 mg. What is the mass of three such tablets rounded to the proper number of significant digits?

1. 0.760 grams2. 0.759 grams3. 0.7590 grams4. 0.253 grams

ANSWERChoice 2 provides three significant digits (and accurate math work). 3 tablets 253 milligrams = 759 milligrams, then dividing by 1,000 converts the milligrams to grams. Note the three is a count of the number of objects, not a measured quantity and 759 retains the same number of significant digits as the least found in related measurements.

Section 1.5: Significant Figures and Calculations

Conversion Factor Method (Dimensional Analysis)

• Qualitative Descriptions vs. Quantitative• Use exact numbers / “scale factor” UNITS• A Bookkeeping Method: Example

___ ft___in --------> ? m• (1 ft = 12 in; 2.54 cm = 1 in; 100 cm = 1 m)• ___ft x 12 in/ft + ___in = ___in• ___in x 2.54 cm/in x 1 m/100cm = ___m

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55 55

55 55 6565

65651.6511.651

Density

• Density = Mass / Volume [g/mL or g/cm3; g/L]

• Least dense man-made solid substance: Aerogel, D = 3.025 x 10-3 g/cm3

http://eetd.lbl.gov/ECS/aerogels/aerogels.htm

http://stardust.jpl.nasa.gov/spacecraft/aerogel.html

• Dair = 1.22 x 10-3 g/cm3 (1.22 g/L)

• Densest known substance: a White Dwarfhttp://antwrp.gsfc.nasa.gov/apod/ap961203.html

1.0 teaspoon = 3.0 T; D = ? g/cm3 (1 tsp = 4.93 mL; 1 mL = 1 cm3 )

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QUESTIONWhich would provide more grams of NaCl, sample one with a mass of 2,350 mg, or sample two, a solid with a volume of 2.00 cm3? (The density of solid salt is 2.16 g/cm3.) Report your choice and report the grams of the more massive sample.

1. Sample two; 1.08 grams2. Sample two; 4.32 grams3. Sample one; 2.35 grams4. Sample one; 2.350 grams

ANSWERChoice 2 provides the accurate mass for 2.00 cm3 of salt. This mass is larger than the 2.35 gram sample. Be sure to solve for the mass of a sample from its density and volume by multiplying 2.00 cm3 × 2.16 g/cm3.

Section 1.8: Density

Densities of Various Common Substances* at 20° C

QUESTIONThe volume of a sample can be obtained from its density and mass. If the mass of a sample of acid from a battery were 5.00 grams and the density was 1.2 g/mL, what would you report in mL and with the proper number of significant digits, as the sample volume?

1. 6.0 mL2. 6.00 mL3. 4.2 mL4. 4.17 mL

ANSWERChoice 3 shows the correct volume for 5.00 grams of this sample. First, be sure to use the correct solution for solving volume from mass and density (V = m/D). Then recall that the significant digit pattern for dividing measurements is to retain the same number of significant digits in the answer as the least number in any of the related measurements.

Section 1.8: Density

Percent

• A comparison based on normalization to 100.

• George Washington University: 64 unsealed addressed envelopes with $10 in each were dropped on campus in different classrooms.

• In economics 18 of 32 were mailed, in business, history and psychology 10 of 32 were mailed. What is the percent for each of the 2 groups of students?

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Percent Continued

• The Professor conducting the study received 43.75% of the $640 in the mail. How much did he receive?

• How many of you would mail the envelop presuming no one knows you found it?

• One student mailed an empty envelop with the return address: Mr. IOU, 1013 Indebted Lane, Bankrupt City, MS (WSJ 1/18/95)

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© Copyright 1998-2007 R.J. Rusay