Chapter 1

Matter & Measurement

Chemistry is…

…the study of the composition, structure, and properties of matter and the changes it undergoes

C2H5OH + 3 O2 2 CO2 + 3 H2O + Energy

Reactants Products

MatterMatterAnything that has mass and occupies space

MasMasssA measure of the

amount of matter

AtomAtomThe smallest unit of an element that maintainsthe properties of that elementElementElement

A pure substance made of only one kind of atom

Properties of Properties of MatterMatterExtensive propertiesExtensive properties

Intensive propertiesIntensive properties

Volume

Mass

Energy 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

Physical Physical ChangeChangeA change in a substance that does not involve a change in the identity of the substance.

Example:

Phase Changes

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.

Three PhasesThree Phases

Copper Phases - SolidCopper Phases - Solid

Copper Phases - LiquidCopper Phases - Liquid

Copper Phases – Vapor Copper Phases – Vapor (gas)(gas)

Chemical ChangeChemical ChangeA change in which one or more substances are converted into different substances.

Heat and light are often evidence of a chemical change.

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.

Filtration:

Separation of a MixtureSeparation of a Mixture

Distillation

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

Measurement

Nature of Measurement

•

Part 1 - Part 1 - numbernumber Part 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

The Fundamental SI Units (le Système International, SI)

SI PrefixesCommon to Chemistry

Prefix Unit Abbr.

Exponent

Kilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro 10-6

Temperature Scales

The Thermometero Determine the temperature by reading the scale on the thermometer at eye level.o Read the temperature by using all certain digits and one uncertain digit. o Certain digits are determined from the

calibration marks on the thermometer. o The uncertain digit (the last digit of the reading) is estimated. o On most thermometers encountered in a general chemistry lab, the tenths place is the uncertain digit.

Do not allow the tip to touch the walls or the bottom of the flask.

If the thermometer bulb touches the flask, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.

Reading the ThermometerDetermine the readings as shown below on Celsius thermometers:

_ _ . _ C _ _ . _ C8 7 4 3 5 0

Volume Instruments

Reading the Meniscus

Always read volume from the bottom of the meniscus. The meniscus is the curved surface of a liquid in a narrow cylindrical container.

Try to avoid parallax errors.ParallaxParallax errorserrors arise when a meniscus or arise when a meniscus or needle is viewed from an angle rather than needle is viewed from an angle rather than from straight-on at eye level.from straight-on at eye level.

Correct: Viewing the meniscus

at eye level

Incorrect: viewing the meniscus

from an angle

Measuring Volume Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level. Read the volume using all certain digits and one uncertain digit.

Certain digits are determined from the calibration marks on the cylinder. The uncertain digit (the last digit of the reading) is estimated.

Use the graduations to find all certain digits

There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are…

52 mL.

Estimate the uncertain digit and take a reading

The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is .

The volume in the graduated cylinder is

0.8 mL

52.8 mL.

10 mL GraduateWhat is the volume of liquid in the graduate?

_ . _ _ mL6 26

Uncertainty in Measurement

• A A digit that must be digit that must be estimatedestimated is is called called uncertainuncertain. A . A measurementmeasurement always has some degree of uncertainty.always has some degree of uncertainty.

Why Is there Uncertainty? Measurements are performed with instruments No instrument can read to an infinite number of decimal placesWhich of these balances has the greatest

uncertainty in measurement?

Precision 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 refers to the degree of agreement among several measurements agreement among several measurements made in the same manner.made in the same manner.

Neither accurate nor

precise

Precise but not accurate

Precise AND accurate

Significant Digits: Atlantic/ Pacific Rule

• Atlantic -

• When the decimal is ABSENT, go to the Atlantic side of the number, start counting digits when you reach a non-zero number. Record

Practice

• 45,000 hrs

• 78,700 kilometers

• 3,000 liters

• two

• three

• one

• Pacific - when the decimal is PRESENT, go to the Pacific side of the number, start counting digits when you reach a non-zero number

Practice

• .009999 grams

• 560.03 mL

• 100.0 meters

• .00506

• 4

• 5

• 4

• none

Rules for Counting Significant Figures - Details

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

• 34563456 hashas

• 44 sig figs.sig figs.

Rules for Counting Significant Figures - Details

• ZerosZeros• -- Captive zeros Captive zeros always count always count

asassignificant figures.significant figures.

• 16.07 16.07 hashas

• 44 sig figs. sig figs.

More practice

• 56,000,000 seconds• 33,000 candles• 60900 milligrams• .899000 centimeters• .6700 meters

2 0 * 3 6 4

Sig 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

Density – a derived measure

value is found through mathematical computation

D=Mass/ Volume

In science, we deal with some In science, we deal with some very very LARGELARGE numbers: numbers:

1 mole = 6020000000000000000000001 mole = 602000000000000000000000

In science, we deal with some In science, we deal with some very very SMALLSMALL numbers: numbers:

Mass of an electron =Mass of an electron =0.000000000000000000000000000000091 kg0.000000000000000000000000000000091 kg

Scientific NotationScientific Notation

2 500 000 000

Step #1: Insert an understood decimal pointStep #1: Insert an understood decimal point

.

Step #2: Decide where the decimal Step #2: Decide where the decimal must end must end up so that one number is to its up so that one number is to its leftleftStep #3: Count how many places you Step #3: Count how many places you bounce bounce the decimal pointthe decimal point

123456789

Step #4: Re-write in the form M x 10Step #4: Re-write in the form M x 10nn

2.5 x 102.5 x 1099

The exponent is the number of places we moved the decimal.

0.00005790.0000579

Step #2: Decide where the decimal Step #2: Decide where the decimal must end must end up so that one number is to its up so that one number is to its leftleftStep #3: Count how many places you Step #3: Count how many places you bounce bounce the decimal pointthe decimal pointStep #4: Re-write in the form M x 10Step #4: Re-write in the form M x 10nn

1 2 3 4 5

5.79 x 105.79 x 10-5-5

The exponent is negative because the number we started with was less than 1.