Chemical Foundations Chemical Foundations 1
Mar 15, 2016
Chemical Chemical FoundationsFoundations
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Nature of MeasurementNature of Measurement
Part 1 - Part 1 - numbernumberPart 2 - Part 2 - scale (unit)scale (unit)
Examples:Examples:2020 gramsgrams
6.63 x 106.63 x 10-34-34 Joule secondsJoule seconds
Measurement - quantitative Measurement - quantitative observation observation consisting of 2 partsconsisting of 2 parts
Uncertainty in MeasurementUncertainty in MeasurementA digit that must be A digit that must be estimatedestimated is called is called uncertainuncertain. A . A measurementmeasurement always has always has some degree of uncertainty.some degree of uncertainty. Measurements are performed with instruments No instrument can read to an infinite number of decimal places
Ex: Reading a MeterstickEx: Reading a Meterstick. l. l22. . . . I . . . . I. . . . I . . . . I33 . . . .I . . . . I . . . .I . . . . I44. . cm. . cm
First digit (known)First digit (known) = 2 = 2 2.?? cm2.?? cmSecond digit (known)Second digit (known) = 0.7 = 0.7 2.7? cm2.7? cmThird digit (estimated) between 0.05- 0.07Third digit (estimated) between 0.05- 0.07Length reportedLength reported == 2.75 cm 2.75 cm
oror 2.74 cm 2.74 cm oror 2.76 cm2.76 cm
Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details1. Nonzero integersNonzero integers always count as always count as significant figures.significant figures.
34563456 hashas 44 sig figs.sig figs.
Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details
Note: “leading” means ANY zero that appears before the first nonzero digit, whether the zeros are before OR after a decimal.
ZerosZeros-- 2. 2. Leading zerosLeading zeros do not count do not count as as
significant figures.significant figures.
0.04860.0486 has has33 sig figs. sig figs.
Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details
ZerosZeros-- 3. 3. Sandwiched zeros Sandwiched zeros always always
count ascount assignificant figures.significant figures.
16.07 16.07 hashas44 sig figs. sig figs.
Note: “sandwiched” means zeros that appears between nonzero digits
Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details
ZerosZeros4. 4. Trailing zerosTrailing zeros are significant are significant only if the number contains a only if the number contains a decimal point.decimal point.
9.3009.300 has has44 sig figs. sig figs.
Note: “trailing” means ALL zeros that appear after the last nonzero digit
Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details5. Exact numbersExact numbers have an infinite have an infinite number of significant figures.number of significant figures.
11 inch = inch = 2.542.54 cm, exactlycm, exactly
Sig Fig Practice #1Sig Fig Practice #1How many significant figures in each of the following?1.0070 m
5 sig figs
17.10 kg 4 sig figs
100,890 L 5 sig figs
3.29 x 103 s 3 sig figs0.0054 cm 2 sig figs3,200,000 2 sig figs
Rules for Significant Figures in Rules for Significant Figures in Mathematical OperationsMathematical Operations
#1.Multiplication and DivisionMultiplication and Division:: # # sig figs sig figs in the result equals the in the result equals the number in the least precise number in the least precise measurement used in the measurement used in the calculation.calculation.
6.38 x 2.0 =6.38 x 2.0 =12.76 12.76 13 (2 sig figs)13 (2 sig figs)
Sig Fig Practice #2Sig Fig Practice #2
3.24 m x 7.0 mCalculation Calculator says: Answer
22.68 m2 23 m2
100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 4.22 g/cm3
0.02 cm x 2.371 cm 0.04742 cm2 0.05 cm2
710 m ÷ 3.0 s 236.6666667 m/s 240 m/s1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft
1.030 g x 2.87 mL 2.9561 g/mL 2.96 g/mL
Rules for Significant Figures Rules for Significant Figures in Mathematical Operationsin Mathematical Operations#2: Addition and SubtractionAddition and Subtraction: The : The number of number of decimal placesdecimal places in the result in the result equals the number of decimal places in equals the number of decimal places in the least precise measurement.the least precise measurement.
6.6.88 + 11.934 =18.734 + 11.934 =18.734 18. 18.77
((1 decimal place1 decimal place, , 3 sig figs3 sig figs))
Sig Fig Practice #3Sig Fig Practice #3
3.24 m + 7.0 mCalculation Calculator says: Answer
10.24 m 10.2 m100.0 g - 23.73 g 76.27 g 76.3 g
0.02 cm + 2.371 cm 2.391 cm 2.39 cm713.1 L - 3.872 L 709.228 L 709.2 L1818.2 lb + 3.37 lb 1821.57 lb 1821.6
lb2.030 mL - 1.870 mL 0.16 mL 0.160 mL
Rules for Rounding AnswersRules for Rounding Answers
1. Complete all calculations, then round ONLY the final answer.
2. Identify the correct digit to round (the last sig fig).ex: 18.734
3. Look ONLY at the number immediately to the right of this digit: 18.734» If this number is 5 or greater, round
the last sig fig up.» If this number is less than 5, the last
sig fig remains the same. 18.7
The Fundamental SI UnitsThe Fundamental SI Units (le Système International, SI)(le Système International, SI)
Physical Quantity Name AbbreviationMass kilogram kgLength meter mTime second sTemperature Kelvin KElectric Current Ampere AAmount of Substance mole molLuminous Intensity candela cd
SI UnitsSI Units
SI Prefixes Common to ChemistrySI Prefixes Common to ChemistryPrefix Unit Abbr. ExponentMega M 106
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro 10-6
Nano n 10-9
Pico p 10-12
Precision and AccuracyPrecision and AccuracyAccuracyAccuracy refers to the agreement of a refers to the agreement of a particular value with the particular value with the truetrue value.value.PrecisionPrecision refers to the degree of agreement refers to the degree of agreement among several measurements made in the among several measurements made in the same manner.same manner.
Neither accurate nor
precise
Precise but not accurate
Precise AND accurate
Types of ErrorTypes of ErrorRandom ErrorRandom Error (Indeterminate Error) - (Indeterminate Error) - measurement has an equal probability of measurement has an equal probability of being high or low.being high or low.
Systematic ErrorSystematic Error (Determinate Error) - (Determinate Error) - Occurs in the Occurs in the same directionsame direction each time each time (high or low), often resulting from poor (high or low), often resulting from poor technique or incorrect calibration. technique or incorrect calibration. This can This can result in measurements that are precise, result in measurements that are precise, but not accurate.but not accurate.
Error Analysis PracticeError Analysis PracticeEx 1: The data collected when the same
sample of silver was weighed five times is as follows:
2.31g, 2.51g, 2.30g, 2.44g, 2.40g
The actual mass of the silver is 2.71.
Are the student’s measurements accurate?Are they precise?
Practice: Section 1.3 & 1.4 # 3, 4, 6.
Dimensional AnalysisDimensional AnalysisThere are times when you need to change the units in
which a measurement is expressed.
Ex: You might want to convert from hours to minutes.
6.2 hours = ? minutes
To do so, you must find the defined relationship between the 2 units.
1 hour = 60 minutes
Dimensional AnalysisDimensional Analysis
Then create a conversion factor that will cancel the units of your given value.
Conversion FactorsConversion FactorsFractions in which the numerator and Fractions in which the numerator and
denominator are EQUAL quantities expressed denominator are EQUAL quantities expressed in different unitsin different unitsExample: 1 hr. = 60 min
Factors: 1 hr. and 60 min60 min 1 hr.
Which one of these conversion factors will cancel the units of our given value, 6.2 hours?
Conversion FactorsConversion Factors
6.2 hours x 1 hour = ? Minutes 60 min.
OR
6.2 hours x 60 min = ? Minutes 1 hour
The second conv. factor allows us to cancel the hour units (since “hr” appears in numerator & denominator) so this is the one we want.
Multi-step ConversionsMulti-step Conversions
• Sometimes you must use more than one conversion factor.
• When there isn’t a direct relationship between the 2 units of interest.
Multi-step Conversions, cont.Multi-step Conversions, cont.
How many seconds are in 1.4 days?Unit plan: days hr min secondsDefined Relationships: 1 day = 24 hr
1 hr = 60 min1 min = 60 s
1.4 days x 24 hr x 60 min x 60 s = 1 day 1 hr 1 min
ANSWER: 120,960 s.
Complex ConversionsComplex Conversions• Sometimes it is necessary to convert with
measurements that involve more than one unit!
• Ex: convert 60 mi/hr into ft/sec• 1 mile=5280 ft 1 hr=60 min 1 min=60
sec
60mi x 5280 ft 1 hr x 1 min = 90 ft/sec hr 1 mi 60 min 60 sec 1
Summary: Dimensional Summary: Dimensional AnalysisAnalysis
By using dimensional analysis the UNITS ensure By using dimensional analysis the UNITS ensure that you have the conversion right side up, and that you have the conversion right side up, and the UNITS are calculated as well as the numbers!the UNITS are calculated as well as the numbers!
ASSIGNMENT: Study Guide, Section 1.6, ASSIGNMENT: Study Guide, Section 1.6, #15-18, 24-26#15-18, 24-26p 16-17p 16-17
Steps in the Scientific MethodSteps in the Scientific Method1.1.ObservationsObservations
-- quantitativequantitative- - qualitativequalitative
2.2. Formulating hypothesesFormulating hypotheses- - possible explanation for the possible explanation for the observationobservation
3.3. Performing experimentsPerforming experiments- - gathering new information to gathering new information to decidedecide
whether the hypothesis is validwhether the hypothesis is valid
Outcomes Over the Long-Outcomes Over the Long-TermTerm
Theory (Model)Theory (Model)- - A set of tested hypotheses that give anA set of tested hypotheses that give an overall explanation of some natural overall explanation of some natural
phenomenon.phenomenon.Natural LawNatural Law
-- The same observation applies to many The same observation applies to many different systemsdifferent systems
-- Example - Law of Conservation of MassExample - Law of Conservation of Mass
Law vs. TheoryLaw vs. Theory
A A lawlaw summarizes what happens summarizes what happens
A A theorytheory (model) is an attempt to explain (model) is an attempt to explain whywhy it happens.it happens.
Converting Celsius to KelvinConverting Celsius to Kelvin
33Kelvins = C + 273 °C = Kelvins - 273
DensityDensity
• Is a physical property of matter & can help you identify unknown element samples.
• Is the amount of mass per volume.• Often expressed in g/mL
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Properties of Properties of MatterMatterExtensive propertiesExtensive properties
Intensive propertiesIntensive properties
VolumeMass
Energy Content (think Calories!)
depend on the amount of matter that is present.
do not depend on the amount of matter present.
Melting pointBoiling pointDensity
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Three PhasesThree Phases
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Phase Phase DifferencesDifferences
SolidSolid – definite volume and shape; particles packed in fixed positions.LiquidLiquid – definite volume but indefinite shape; particles close together but not in fixed positionsGasGas – neither definite volume nor definite shape; particles are at great distances from one anotherPlasma – high temperature, ionized phase of matter as found on the sun.
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Classification of Matter
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Separation of a MixtureSeparation of a Mixture
The constituents of the mixture retain The constituents of the mixture retain their identity and may be separated by their identity and may be separated by physical means.physical means.
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Separation of a MixtureSeparation of a Mixture
The components of dyes such as ink may be separated by paper chromatography.
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Separation of a Separation of a Mixture By Mixture By DistillationDistillation
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Organization of MatterOrganization of Matter MatterMatter
Mixtures:a) Homogeneous (Solutions)b) Heterogeneous
Pure SubstancesPure Substances
Compounds ElementsElements
AtomsAtoms
NucleusNucleus ElectronsElectrons
Protons NeutronsNeutrons
QuarksQuarks QuarksQuarks
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Separation of a CompoundSeparation of a CompoundThe Electrolysis of water
Water Hydrogen + OxygenH2O H2 + O2
Reactant Products
Compounds must be separated by chemical means.With the application of electricity, water can be separated into its elements
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