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Calculations And Matter, Measurements Chem101 - Lecture 1 · PDF fileMatter, Measurements And...

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Chem101 - Lecture 1 Matter, Measurements And Calculations
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Chem101 - Lecture 1

Matter, Measurements

And

Calculations

University of Wisconsin-Eau Claire Chem101 - Lecture 1 2

What is Chemistry?

• Chemistry is the study of matter

• Much of what we interact with in theworld around us is made up of matter.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 3

What then is matter?

• Matter is anything that has mass andoccupies space (has volume)

University of Wisconsin-Eau Claire Chem101 - Lecture 1 4

Then what is mass?

• Mass is a measurement of the amountof matter in a object- These definitions may seem cyclical to

you.

- We will see that mass is directly related tothe number of atoms that an objectcontains.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 5

Then what is mass?

• In physics we learn that an object’smass is equivalent to its inertia.- It is a measure of how much an object

resists changes in its velocity or directionof movement.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 6

Exercise 1.1

A heavy steel ball is suspended by a thin wire. Theball is hit from the side with a hammer, but hardlymoves. Describe what you think would happen if thisidentical experiment were carried out on the moon.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 7

What is weight?

• Weight is the force that an objectexerts on another object due togravitational attraction.

• Weight is directly proportional tomass- This is why the Earth has such a strong

attraction for objects.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 8

What is weight?

• At the surface of the Earth theproportionality constant, relatingweight to mass, is essentially thesame everywhere.

• This allows us to use the two terms(mass and weight) interchangeably.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 9

Measuring mass and weight

• In lab you will learn- That the mass of an object is determined

using a balance,

- While the weight of an object isdetermined using a scale.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 10

Properties and Changes

• Properties are the characteristics ofan object that allow us to distinguishit from other objects.

• There are two basic categories ofproperties:- Physical properties- Chemical properties

University of Wisconsin-Eau Claire Chem101 - Lecture 1 11

Physical Properties

• Physical properties of matter areproperties that can be observed ormeasured without trying to changethe composition of the matter beingobserved.

• For example- Color, size, density, melting point, et al.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 12

Chemical Properties

• Chemical properties of matter areproperties that are observed when anattempt is made to change thecomposition of the matter.

• For example- Paper burns easily.

- Glass does not

• When paper burns, its compositionchanges.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 13

Chemical Change

• Burning a piece of paper is anexample of a chemical change.

• Chemical change occurs wheneverthe composition of a substancechanges.

• When a chemical change occurs thephysical properties of the matter alsochange.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 14

Physical Change

• The physical properties of matter canchange, however, without a chemicalchange.

• For example- When ice melts to form liquid water

- When liquid water evaporates to formwater vapor

• Such changes are called physicalchanges.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 15

Exercise 1.9

Classify each of the following properties asphysical or chemical. Explain your reason foreach.

a. Iron melts at 1535°C.b. Alcohol is very flammable.c. The metal used in artificial hip-joints

implants is not corroded by body fluids.d. A 1-in. cube of aluminum weighs less

than 1-in. cube of lead.e. Gasoline burns readily.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 16

A Model of Matter

• Scientific models are used to help us“visualize” and understand thebehavior of nature.

• Models are devised through anditerative process of- Scientific observation

- Formulation of hypotheses

- Testing of hypotheses

University of Wisconsin-Eau Claire Chem101 - Lecture 1 17

Observations about Gases

• At constant temperature the volume ofa gas changes with pressure:- Increasing pressure decreases volume

- Decreasing pressure increases volume

• At constant volume the pressure of agas changes with temperature:- Increasing temperature increases pressure

- Decreasing temperature decreases pressure

University of Wisconsin-Eau Claire Chem101 - Lecture 1 18

Observations about Gases

• Gases have mass.

• Gases mix rapidly with one anotherwhen brought together.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 19

A Model of Matter

• All matter is made up of very tinyparticles.- Early on these particles were called

molecules.

• We now know that molecules makeup many, but not all, substances.- For now we will consider only those

substances that are made up of molecules.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 20

A Model of Matter

• For gases, these molecules moverapidly about colliding with eachother and with the walls of thecontainer:

University of Wisconsin-Eau Claire Chem101 - Lecture 1 21

A Model of Matter

• A molecule is the smallest particle ofa pure substance that has theproperties of that substance and iscapable of stable independentexistence.

• A molecule is the limit of physicalsubdivision of a pure substance.- Any further subdivision can only be done

chemically, by changing the compositionof the substance.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 22

A Model of Matter

• A molecule can be chemicallyseparated into smaller particles calledatoms.- Circles are often used to graphically

represent atoms:

Oxygen Carbon monoxide Carbon dioxide

University of Wisconsin-Eau Claire Chem101 - Lecture 1 23

Types of Molecules• Diatomic

- Contain two atoms

• Triatomic- Contain three atoms

• Polyatomic- Contain more than three atoms

• Homoatomic- Contain only one type of atom

• Heteratomic- Contain more than one type of atom

University of Wisconsin-Eau Claire Chem101 - Lecture 1 24

Exercise 1.13A sample of solid elemental (homoatomic) phosphorus thatis deep read in color is burned. While the phosphorus isburning, a white smoke is produced that is actually a finelydivided solid. The white solid is collected.

a. Have the molecules of phosphorus been changedby the process of burning? Explain.

b. Is the collected white solid a different substancefrom the phosphorus? Explain.

c. In terms of the number of atoms contained, howdo you think the size of the molecules of thewhite solid compares with the size of themolecules of phosphorus? Explain.

d. Classify the molecules of the collected whitesolid using the terms homoatomic andheteroatomic. Explain your reasoning.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 25

Classification of Matter

• Given a sample of matter,- Is it a pure substance

or

- Is it a mixture

• It has to be one or the other

University of Wisconsin-Eau Claire Chem101 - Lecture 1 26

Pure Substances

• A pure substance is matter that has aconstant composition and fixedproperties.

• This is because all of its moleculesare identical.

• Oxygen, carbon dioxide, watersucrose and aluminum are examplesof pure substances.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 27

Mixtures

• A mixture is a physical blend ofmatter that can be physicallyseparated into two or morecomponents, which are themselvespure substances.

• In a mixture not all of the moleculesare identical.

• Air, sugar water and steel areexamples of mixtures.

• Most samples of matter are mixtures.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 28

Pure Substances vs. Mixtures• Pure substances have a fixed set of

physical properties

• The physical properties of mixturesdepend on the relative amounts of itscomponents.

• The physical properties of a mixtureresemble an average of the physicalproperties of its constituentcomponents.- In a mixture the components do not lose

their physical identity.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 29

Classification of Matter• Homogeneous matter has the same

properties throughout the sample.- All pure substances are homogeneous.

• Homogenous mixtures are calledsolutions.- Sugar water is a homogeneous mixture

(solution).

• Mixtures that are not homogeneousare heterogeneous mixtures.- A mixture of sand and sugar is a

heterogeneous mixture.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 30

Classification of Pure Substances

• Elements are pure substances that aremade of homoatomic molecules.- Oxygen, nitrogen, carbon and mercury are

examples of elements.

- The periodic table is an arrangement ofall the elements.

• Compounds are pure substances thatare made of heteratomic molecules.- Carbon monoxide, carbon dioxide, water

and sugar are examples of compounds.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 31

Exercise 1.19

Classify each pure substance represented below by acapital letter as an element or a compound. Indicate whensuch a classification cannot e made and explain why.

a. Two elements when mixed combine to form onlysubstance L .

b. An element and a compound when mixed formsubstances M and Q.

c. Substance X is not change by heating.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 32

Exercise 1.23

Classify each of the following as homogeneous orheterogeneous.

a. Muddy flood water.b. Gelatin dessert.c. Normal urined. Smog-filled aire. An applef. Mouthwashg. Petroleum jelly.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 33

Measurement Units• Units give numbers meaning

- 1 meter

- 10 pounds

- 23 seconds

• Nearly all of the numbers we will beworking with have units.- If you fail to give the units for these

numbers they will be meaningless!

- Advice: Do not give meaningless answersto problems.

University of Wisconsin-Eau Claire Chem101 - Lecture 1 34

The metric system

• We will be using the metric system ofunits.

• Like our number system, the metricsystem is a decimal system.

• It contains only a few basic units- These include:

Mass - gram

Length - meter

Time - second

University of Wisconsin-Eau Claire Chem101 - Lecture 1 35

The metric system

• Most of the units in the metric systemare derived units:

- Area - meter x meter = m2

- Volume - meter x meter x meter = m3

- Velocity -

- Energy -

meterond

m ssec=

kilogram meter metersecond second

kgms

Joulex xx

= =2

2


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