Introduction to Introduction to Chemistry:Chemistry:

MatterMatter

Basic ChemistryBasic ChemistryChapter 2Chapter 2

Rev. 1/15/02

The study of matter is The study of matter is central to the study of central to the study of

chemistry.chemistry.Q. What is matter?Q. What is matter?

A. Matter is anything that … A. Matter is anything that …

… … has mass, has mass,

… … and takes up space.and takes up space.

What are some What are some things that are things that are

matter?matter?

If it’s not matter, If it’s not matter, what is it?what is it?EnergyEnergyEnergyEnergy

HeatHeatLightLight Kinetic energyKinetic energy

Do things you cannot see Do things you cannot see have mass?have mass?

What about air?What about air?

How would you experimentally How would you experimentally determine that air has mass?determine that air has mass?

A column of air 1 inch square at the A column of air 1 inch square at the base and as tall as the atmosphere, base and as tall as the atmosphere, weighs 14.7 pounds at sea level.weighs 14.7 pounds at sea level.

Consider these statements:Consider these statements:

What is the difference What is the difference between mass and weight?between mass and weight?

The mass of the beaker is 215 grams.The mass of the beaker is 215 grams.

The beaker weighs 215 grams.The beaker weighs 215 grams.

Look at the difference Look at the difference between a balance and a between a balance and a

spring scale.spring scale.

A balance compares two masses A balance compares two masses like a “see-saw”.like a “see-saw”.

A spring balance requires a force A spring balance requires a force to stretch the spring.to stretch the spring.

That’s the answer.That’s the answer.Weight is a force. Weight is a force.

To weigh something we must To weigh something we must exert an opposing force.exert an opposing force.

Mass is not a force, it is a Mass is not a force, it is a measure of the quantity of measure of the quantity of matter.matter.

Suppose, on Earth you weigh Suppose, on Earth you weigh 60 kilograms. That means 60 kilograms. That means that you will also have a that you will also have a mass of 60 kilograms.mass of 60 kilograms.

Note: 60 kilograms is about 130 pounds.Note: 60 kilograms is about 130 pounds.

On the surface of the Earth, mass and On the surface of the Earth, mass and weight have the same numerical weight have the same numerical value.value.

But, if you go to the moon…But, if you go to the moon…Take a balance and a spring Take a balance and a spring

scale.scale.

Even though there is no air on the Even though there is no air on the moon, there is still gravity.moon, there is still gravity.

The gravity on the moon is 1/6th The gravity on the moon is 1/6th that of Earth.that of Earth.

On the moon …On the moon …The balance will indicate The balance will indicate

60 kilograms,60 kilograms,

but the spring scale will indicate but the spring scale will indicate 10 kilograms …10 kilograms …

because the force exerted by because the force exerted by gravity is 1/6 that of Earth’s.gravity is 1/6 that of Earth’s.

The bottom line …The bottom line …Scientists tend to use “mass” Scientists tend to use “mass”

and “weight” interchangeably, and “weight” interchangeably, even though they know the even though they know the difference.difference.

We will too.We will too.

Just be sure you know the difference Just be sure you know the difference when it shows up on a test.when it shows up on a test.

Where will you weigh more? Where will you weigh more?

(a)(a) Mt. EverestMt. Everest

(b)(b) Myrtle BeachMyrtle Beach

(c)(c) The bottom of a South The bottom of a South African diamond mineAfrican diamond mine

The Metric The Metric SystemSystem

What are the basic units of What are the basic units of mass, length, volume, mass, length, volume,

temperature and time in the temperature and time in the metric system?metric system?

The metric system …The metric system …

MassMass

LengthLength

VolumeVolume

TemperatureTemperature

TimeTime

GramGram gg

MeterMeter mm

LiterLiter LL

KelvinKelvin KK

SecondSecond ss

What are the commonly What are the commonly used metric prefixes?used metric prefixes?

Mega-Mega-Kilo-Kilo-Centi-Centi-Milli-Milli-Micro-Micro-Nano-Nano-

x 10x 1066 megabyte, megohmmegabyte, megohm

x 10x 1033 kilometer, kilogramkilometer, kilogram

x 10x 10-2-2 centimetercentimeter

x 10x 10-3-3 millimeter, milligrammillimeter, milligram

x 10x 10-6-6 micrometer, microgram micrometer, microgram

x 10x 10-9-9 nanometernanometer

What are the symbols for What are the symbols for the metric prefixes?the metric prefixes?

Mega-Mega-Kilo-Kilo-Centi-Centi-Milli-Milli-Micro-Micro-Nano-Nano-

MM - MB, M- MB, M kk - km, kg- km, kg cc - cm- cm mm - mm, mg, mL- mm, mg, mL - - m, m, g, g, LL nn - nm- nm

DensityDensity

What is density?What is density?Density is the Density is the

ratio of the mass ratio of the mass of an object to of an object to the volume of the volume of the object.the object.

Typical units of density are Typical units of density are grams per milliliter, g/mLgrams per milliliter, g/mL

D = D = mm

VV

Does the density of a Does the density of a substance depend on the substance depend on the amountamount of substance? of substance?

No. The ratio is a constant. No. The ratio is a constant. As you add more As you add more massmass of the of the substance, the substance, the volumevolume increases as well.increases as well.

Does the density of a Does the density of a substance depend on the substance depend on the

temperature of the substance?temperature of the substance?

Yes. But only slightly for solids Yes. But only slightly for solids and liquids. As the temperature and liquids. As the temperature changes, expansion and changes, expansion and contraction occurs, which changes contraction occurs, which changes the volume slightly, but …the volume slightly, but …

The density of a confined gas The density of a confined gas changes dramatically as the changes dramatically as the temperature changes…temperature changes…

… … because the because the volume of a gas volume of a gas depends on the depends on the temperature.temperature.

hotplate

Cylinder with movable piston

Gas

Develop a method to Develop a method to measure the density of a measure the density of a

piece of metal.piece of metal.

What equipment will you need?What equipment will you need?

What data should you take?What data should you take?

How will you analyze the data?How will you analyze the data?

Devise a method to measure Devise a method to measure the density of a liquid.the density of a liquid.

What laboratory equipment will What laboratory equipment will you need?you need?

What kind of data should What kind of data should you take?you take?

How will you analyze the data?How will you analyze the data?

How can you How can you measure the measure the volume of an volume of an odd-shaped odd-shaped solid?solid?

Hint: Hint: ArchimedesArchimedes

Eureka!Eureka!

Liquid DisplacementLiquid Displacement

An object will An object will displace its own displace its own volume of water.volume of water.

Devise a method to Devise a method to measure the density of a measure the density of a

metal cylindermetal cylinderWhat equipment will you need?What equipment will you need?

What data should you take?What data should you take?

How will you analyze the data?How will you analyze the data?

MeasurementsMeasurementsAccuracy and Accuracy and

Precision Precision

Consider four targets and Consider four targets and three shots on each:three shots on each:

Low PrecisionLow PrecisionLow AccuracyLow Accuracy

High PrecisionLow Accuracy

Low PrecisionHigh Accuracy

High PrecisionHigh Accuracy

Precision vs AccuracyPrecision vs Accuracy

Precision – the Precision – the reproducibility of the reproducibility of the measurementmeasurement

Accuracy – the closeness Accuracy – the closeness to the correct answerto the correct answer

Precision is indicated by …Precision is indicated by …An uncertainty in the measurementAn uncertainty in the measurement

5.4 +/- 0.2 mL5.4 +/- 0.2 mL34.56 +/- 0.01 g34.56 +/- 0.01 g19.3 +/- 0.1 cm19.3 +/- 0.1 cm

It wouldn’t make sense to write a It wouldn’t make sense to write a volume as 15.675 mL when the volume as 15.675 mL when the graduated cylinder is only precise to graduated cylinder is only precise to the nearest mL: +/- 1 mLthe nearest mL: +/- 1 mL

Precision is also indicated …Precision is also indicated …

14.7 has 3 significant digits14.7 has 3 significant digits1004 has 4 significant digits1004 has 4 significant digits200. has 3 significant digits200. has 3 significant digits

0.0046 has 2 significant digits0.0046 has 2 significant digits204.70 has 5 significant digits204.70 has 5 significant digits

… … by the number of significant by the number of significant digits in a measurement.digits in a measurement.

Rules for Significant DigitsRules for Significant Digits1.1. All non-zero digits are significant.All non-zero digits are significant.2.2. Zeroes between non-zero digits are Zeroes between non-zero digits are

significant.significant.3.3. Zeroes which are place holders are Zeroes which are place holders are

not significant, unless otherwise not significant, unless otherwise indicated.indicated.

4.4. Zeroes which indicate the level of Zeroes which indicate the level of precision are significant.precision are significant.

ExamplesExamplesa.a. 243.5243.5b.b. 0.04050.0405c.c. 1,9001,900d.d. 100.100.e.e. 0.003600.00360f.f. 304.50304.50

a.a. 44b.b. 33c.c. 22d.d. 33e.e. 33f.f. 55

Precision in calculations:Precision in calculations:The answer can have no more The answer can have no more

precision that the least precise precision that the least precise factor.factor.

In other words: the answer has the In other words: the answer has the same number of significant digits as same number of significant digits as the value with the lowest number of the value with the lowest number of significant digits.significant digits.

Multiply 3.5 cm by 0.251 cm Multiply 3.5 cm by 0.251 cm to get the area.to get the area.

The calculator gives 0.8785 cmThe calculator gives 0.8785 cm22

But we write the answer as 0.88 cmBut we write the answer as 0.88 cm22

3.5 has two significant digits, and 3.5 has two significant digits, and 0.251 has three significant digits …0.251 has three significant digits …

0.88 cm0.88 cm22the answer can only have the answer can only have two significant digits.two significant digits.

A student finds a side of a rectangle A student finds a side of a rectangle to be 3.69 m and another student to be 3.69 m and another student finds the other side to be 12 m.finds the other side to be 12 m.Find the area of the rectangle.Find the area of the rectangle.

A = L x WA = L x WA = 3.69 m x 12 mA = 3.69 m x 12 m

A = 44 mA = 44 m22

Not 44.28, since the answer can have Not 44.28, since the answer can have only two significant digits.only two significant digits.

Do the following calculations and Do the following calculations and express the answer to the correct express the answer to the correct number of significant digits.number of significant digits.

1.1. 45.3 x 0.0031 =45.3 x 0.0031 =

2.2. 0.0850 x 32.2 =0.0850 x 32.2 =

3.3. 65.0 / 20.30 = 65.0 / 20.30 =

4.4. (7.3 x 10(7.3 x 1033)( 3.030 x 10)( 3.030 x 1044) =) =

5.5. 360 / 12 =360 / 12 =

0.140.14

2.742.74

3.203.20

2.2 x 102.2 x 1088

30.30.

Temperature Temperature MeasurementsMeasurements

Temperature is a Temperature is a measure of “how hot measure of “how hot or cold” something is.or cold” something is.

How do we measure temperature?

ThermometerThermometer

Temperature probeTemperature probe

ThermocoupleThermocouple

ColorColor

Temperature ScalesTemperature ScalesK C FK C F

100100

00

-273-273

373373

273273

00

212212

3232

-462-462

Boiling point Boiling point of waterof water

Freezing point of waterFreezing point of water (Melting point of ice)(Melting point of ice)

Absolute zeroAbsolute zero(Coldest possible temp(Coldest possible temp.)

Temperature ConversionsTemperature Conversions

K = C + 273K = C + 273

F = 1.8 C + 32F = 1.8 C + 32

In later projects we will In later projects we will study heat transfer, study heat transfer,

conservation of energy, conservation of energy, and measure the specific and measure the specific heat capacity of a metal.heat capacity of a metal.

Things to find out about:Things to find out about:Temperature and heat changesTemperature and heat changesThe “Law of Conservation of Energy” The “Law of Conservation of Energy” Specific heat capacitySpecific heat capacityThe equation Q = mcThe equation Q = mcTTA procedure to measure the mass and A procedure to measure the mass and

volume of a solid cylinder of metal.volume of a solid cylinder of metal.A procedure to measure the specific A procedure to measure the specific

heat capacity of the metal.heat capacity of the metal.

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