Chemical Foundations

Chapter 1

Chemistry

Chemistry deals with situations in which the nature of a substance is changed by altering its composition so that entirely new substances are synthesized or particular properties of existing substances are enhanced.

Science

Science is both a noun and a verb.

Science is a body of knowledge and a method of adding to that body of

knowledge.

Steps in the Scientific Method

1.1. ObservationsObservations

--quantitative - measurement involves a quantitative - measurement involves a number and a unit.number and a unit.

--qualitativequalitative

2.2. Formulating hypothesesFormulating hypotheses

-- possible explanation for the possible explanation for the observationobservation

3.3. Performing experimentsPerforming experiments

-- gathering new information to decidegathering new information to decide

whether the hypothesis is validwhether the hypothesis is valid

Outcomes Over the Long-Term

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. Theory

A A lawlaw summarizes what happens; summarizes what happens;a a theorytheory (model) is an attempt to (model) is an attempt to explain explain whywhy it happens. it happens.

01_03

Observation

Hypothesis

Experiment

Theory(model)

Experiment

Theorymodifiedas needed

Prediction

Law

The various parts of the scientific method.

Problems of the Scientific Method

Scientists must be objective when using the scientific method. The scientific method is affected by:

profit motives religious beliefs

wars misinterpretation of data

budgets emotions

fads prejudices

politics peer pressure

Nature of Measurement

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

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

Examples:Examples:2020 gramsgrams

6.63 6.63 Joule secondsJoule seconds

International System(le Système International)

Based on metric system and units Based on metric system and units derived from metric system.derived from metric system.

The Fundamental SI Units

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

01_05

1dm3= 1 L

1 cm

1 cm

1m3

1cm3= 1 mL

One liter is defined as a cubic decimeter and 1 mL is onecubic centimeter.

01_06

100908070605040302010

100-mL graduatedcylinder

250-mL volumetric flask50-mL buret25-mL pipet

Calibration markindicates 25-mLvolume

01234

454647484950

mL

mL

Valve (stopcock)controls the liquid flow

Calibration markindicates 250-mLvolume

Common types of laboratory equipment used to measure liquid volume.

Mass & Weight

Mass is a measure of the resistance of an object to a change in its state of motion -- a constant.

Weight is the measure of the pull of gravity on an object and varies with the object’s location.

Uncertainty 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.

01_08

0

10

20

30

40

50

mL

Buret

22.2 mL

Measurement of volume using a buret. The volume is readat the bottom of the meniscus.

Precision and Accuracy

AccuracyAccuracy refers to the agreement of a refers to the agreement of a particular value with the particular value with the true true value.value.

PrecisionPrecision refers to the degree of refers to the degree of agreement among several elements of agreement among several elements of the same quantity.the same quantity.

01_09

(c)(b)(a)

a) is neither precise nor accurate, b) is precise but not accurate (small random, large systematic errors) c) both precise and accurate (small random, no systematic errors.

Types of Error

Random Error Random 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 Error Systematic Error (Determinate Error) - (Determinate Error) - Occurs in the Occurs in the same direction same direction each time each time (high or low), often resulting from poor (high or low), often resulting from poor technique.technique.

AccuracySample Exercise 1.2 on page 13.Trial Graduated Cylinder Buret 1 25 mL 26.54 mL 2 25 mL 26.51 mL 3 25 mL 26.60 mL 4 25 mL 26.49 mL 5 25 mL 26.57 mLAverage 25 mL 26.54 mLWhich is more accurate? Graduated cylinder produces systematic error --value is

too low.

Buret

Exponential Notation

Also called scientific notation and powers of ten notation. Exponential notation has two advantages:

the number of significant digits can easily be indicated

fewer zeros are needed to write a very large or very small number.

Rules for Counting Significant Figures - Overview

1.1. Nonzero integersNonzero integers

2.2. ZerosZeros

-- leading zerosleading zeros

-- captive zeroscaptive zeros

-- trailing zerostrailing zeros

3.3. Exact numbersExact numbers

Rules for Counting Significant Figures - Details

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

34563456 has has

44 sig figs. sig figs.

Rules for Counting Significant Figures - Details

ZerosZeros--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 Significant Figures - Details

ZerosZeros-- Captive zeros Captive zeros always count asalways count as

significant figures.significant figures.

16.07 16.07 hashas

44 sig figs. sig figs.

Rules for Counting Significant Figures - Details

ZerosZeros-- Trailing zerosTrailing zeros are significant onlyare 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 Significant Figures - Details

Exact numbersExact numbers have an have an infiniteinfinite number number of significant figures. Can come from of significant figures. Can come from counting or definition.counting or definition.

15 15 atomsatoms11 inch = inch = 2.542.54 cm, exactlycm, exactly

Rules for Significant Figures in Mathematical Operations

Multiplication and Division:Multiplication and Division: # sig figs # sig figs in the result equals the number in the in the result equals the number in the least preciseleast precise measurement used in the measurement used in the calculation.calculation.

6.38 6.38 2.0 = 2.0 =

12.76 12.76 13 (2 sig figs)13 (2 sig figs)

Rules for Significant Figures in Mathematical Operations

Addition and Subtraction:Addition and Subtraction: # sig figs in # sig figs in the result equals the number of decimal the result equals the number of decimal places in the places in the least preciseleast precise measurement. measurement.

6.8 + 11.934 =6.8 + 11.934 =

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

Rules for Rounding

1. In a series of calculations, carry the extra digits through to the final result, then round.

2. If the digit to be removed

a. is less than five, the preceding digit stays the same.

b. is equal to or greater than five, the preceding digit is increased by 1.

Dimensional Analysis

Also called unit cancellation is a method of solving problems by using unit factors to change from one unit to another.

Unit factor -- the unit that you have goes on bottom, and the unit that you want goes on top.

Dimensional Analysis

Proper use of “unit factors” leads to proper Proper use of “unit factors” leads to proper units in your answer.units in your answer.

OKmile

:.1 0 621371

kilometer0.62137 mile kilometer

NOT OK:1 kilometer

0.62137 mile1 mile

0.62137 kilometer

Dimensional Analysis

What is the dimension of a 25.5 in bicycle frame in centimeters?

(25.5 in)(2.54 cm/1 in) = 64.8 cm

Units must be cancelled and the answer must have correct sig figs, be underlined, and include proper units!!

Temperature

Celsius scale =Celsius scale =CCKelvin scale = KKelvin scale = K

Fahrenheit scale =Fahrenheit scale =FF

01_10

180Fahrenheitdegrees

Boilingpointof water

32F

212F

Freezingpointof water

Fahrenheit

100Celsiusdegrees

Celsius

273.15 K

233.15 K

373.15 K

Kelvin

-40F

100kelvins

0C

100C

-40C

Three major temperature scales.

Temperature

K C

C

1 0 0

F - 3 2

1 8 0

2 7 3 1 5.

Temperature Calculations

Convert - 40.0 oC to Kelvin.

K = C + 273.15

K = -40.0 + 273.15

K = 233.2 K

Temperature Calculations

Convert - 40.0 oC to Fahrenheit.

C

1 0 0

F - 3 2

1 8 0

-4 0 .0

1 0 0

F - 3 2

1 8 0

100 F - 3200 = -7200100 F = -4000 F = - 40.0 oF

Density

DensityDensity is the mass of substance per unitis the mass of substance per unit

volume of the substance:volume of the substance:

density = mass

volume

V

m D

Density Calculations

If an object has a density of 0.7850 g/cm3 and a mass of 19.625 g, what is its volume?

V

m D

D

m V

3cmg

0.7850

g 19.625 V

V = 25.00 cm3

Matter:Matter: Anything Anything occupying space and occupying space and

having mass.having mass.

Classification of Matter

Three States of Matter:Three States of Matter:

Solid: Solid: rigid - fixed volume and shaperigid - fixed volume and shape

Liquid: Liquid: definite volume but assumes the definite volume but assumes the shape of its containershape of its container

Gas: Gas: no fixed volume or shape - assumes no fixed volume or shape - assumes the shape of its containerthe shape of its container

Types of Mixtures

Mixtures have variable composition.Mixtures have variable composition.

AA homogeneous mixture homogeneous mixture is a is a solutionsolution (for example, vinegar)(for example, vinegar)

AA heterogeneous mixture heterogeneous mixture is, to the is, to the naked eye, clearly not uniform (for naked eye, clearly not uniform (for example, a bottle of ranch dressing)example, a bottle of ranch dressing)

HOMOGENEOUS MATTER

- a substance with the same properties throughout -- a pure substance.

Elements and compounds are pure substances (homogeneous matter).

HETEROGENEOUS MATTER

- has different properties throughout -- a mixture.» Salt and pepper» soil» granite» sea water» spaghetti & meat balls

SEPARATION OF MIXTURES

- mixtures can be separated into pure substances by physical means. » distillation» filtration» centrifuging» magnet» evaporation» chromatography

01_13

Thermometer

Vapors

Distillingflask

Burner

Condenser

Receivingflask

Distillate

Water out Coolwater in

Simple laboratory distillation apparatus.

CENTRIFUGE

Paper Chromatography

Chromatography has two phases of matter: a stationaryphase (the paper) and a mobile phase ( the liquid).

Compounds & Elements

Element:Element: A substance that cannot be A substance that cannot be decomposed into simpler substances by decomposed into simpler substances by chemical means.chemical means.

Compound:Compound: A substance with a A substance with a constant composition that can be constant composition that can be broken down into elements by broken down into elements by chemical processes.chemical processes.

UniverseUniverse

MatterMatterEnergyEnergy

HomogeneousHomogeneousPhysical Change HeterogeneousHeterogeneous

Pure SubstancePure Substance SolutionSolution MixtureMixture

ElementElement CompoundCompoundChemical Change

Electron LevelsElectron LevelsNucleusNucleus

ElectronsElectrons ProtonsProtons NeutronsNeutrons

Potential Energy

Potential Energy

Kinetic Energy

Kinetic Energy

PositionPositionCompositionComposition

GravitationalGravitational ElectrostaticElectrostatic

“TO BUILD FROM MATTER IS SUBLIMELY GREAT, BUT GODS AND POETS

ONLY CAN CREATE.”

Pitt