Chemical Chemical FoundationsFoundations

Steps in a Scientific Method Steps in a Scientific Method (depends on particular problem)(depends on particular problem)

1. Observations- quantitative - qualitative

2. Formulating hypotheses - possible explanation for the

observation 3. Performing experiments

- gathering new information to decide

whether the hypothesis is valid

Law vs. TheoryLaw vs. Theory

• A A lawlaw summarizes what happens summarizes what happens (observational)(observational)

• A A theorytheory (model) is an attempt to explain (model) is an attempt to explain whywhy it happens (explanitory)it happens (explanitory)

Nature of MeasurementNature of Measurement

•

Part 1 - Part 1 - number number Part 2 - Part 2 - scale (unit) scale (unit)

Examples: Examples: 2020 grams grams

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

The Fundamental SI UnitsThe Fundamental SI Units (le Système International, SI)(le Système International, SI)

Physical Quantity Name Abbreviation

Mass kilogram kg

Length meter m

Time second s

Temperature Kelvin K

Electric Current Ampere A

Amount of Substance mole mol

Luminous Intensity candela cd

SI UnitsSI Units

SI Prefixes Common to ChemistrySI Prefixes Common to Chemistry

Prefix Unit Abbr. Exponent

Mega 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

Uncertainty in MeasurementUncertainty in Measurement

• A digit that must be A digit that must be estimatedestimated is is called called uncertainuncertain. A . A measurementmeasurement always has some degree of always has some degree of uncertainty.uncertainty. Measurements are performed with instruments No instrument can read to an infinite number of decimal places

Precision and AccuracyPrecision and Accuracy• AccuracyAccuracy 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 Error

• Random 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.

Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details

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

34563456 hashas

44 sig figs.sig figs.

Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details

• Zeros Zeros -- Leading zerosLeading zeros do not count as do not count as

significant figures. significant figures.

• 0.04860.0486 has has

33 sig figs. sig figs.

Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details

• Zeros Zeros -- Captive zeros Captive zeros always count always count

as as significant figures. significant figures.

• 16.07 16.07 has has

44 sig figs. sig figs.

Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details

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

9.3009.300 has has

44 sig figs. sig figs.

Rules for Counting Rules for Counting Significant Figures - DetailsSignificant Figures - Details

• 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 figs

0.0054 cm 2 sig figs

3,200,000 2 sig figs

Rules for Significant Figures in Rules for Significant Figures in Mathematical OperationsMathematical Operations

• Multiplication and DivisionMultiplication and Division:: # # sig figs in the result equals the sig figs 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 m

Calculation 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/s

1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft

1.030 g ÷ 2.87 mL 2.9561 g/mL 2.96 g/mL

Rules for Significant Figures Rules for Significant Figures in Mathematical Operationsin Mathematical Operations

• Addition and SubtractionAddition and Subtraction: The : The number of decimal places in the number of decimal places in the result equals the number of decimal result equals the number of decimal places in the least precise places in the least precise measurement. measurement.

6.8 + 11.934 = 6.8 + 11.934 =

18.734 18.734 18.7 ( 18.7 (3 sig figs3 sig figs))

Sig Fig Practice #3Sig Fig Practice #3

3.24 m + 7.0 m

Calculation Calculator says: Answer

10.24 m 10.2 m

100.0 g - 23.73 g 76.27 g 76.3 g

0.02 cm + 2.371 cm 2.391 cm 2.39 cm

713.1 L - 3.872 L 709.228 L 709.2 L

1818.2 lb + 3.37 lb 1821.57 lb 1821.6 lb

2.030 mL - 1.870 mL 0.16 mL 0.160 mL

Converting Celsius to KelvinConverting Celsius to Kelvin

Kelvins = C + 273 °C = Kelvins - 273

Properties of Properties of MatterMatterExtensive propertiesExtensive properties

Intensive propertiesIntensive properties

Volume

MassEnergy Content (think Calories!)

depend on the amount of matter that is present.

do not depend on the amount of matter present.

Melting point

Boiling point

Density

Three PhasesThree Phases

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.

Classification of Matter

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.

Separation of a MixtureSeparation of a Mixture

The components of dyes such as ink may be separated by paper chromatography.

Separation of a MixtureSeparation of a Mixture

Distillation

Organization of MatterOrganization of Matter

MatterMatter

Mixtures: a) Homogeneous (Solutions) b) Heterogeneous

Pure SubstancesPure Substances

Compounds ElementsElements

AtomsAtoms

NucleusNucleus ElectronsElectrons

Protons NeutronsNeutrons

QuarksQuarks QuarksQuarks

Separation of a CompoundSeparation of a CompoundThe Electrolysis of water

Water Hydrogen + Oxygen

H2O H2 + O2

Reactant Products

Compounds must be separated by chemical means.

With the application of electricity, water can be separated into its elements