Kelter P., Mosher M., Scott A. Chemistry. The Practical Science

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xxxii Features of the Textbook Program

The World

of Chemistry

Scientists are not especially different

from anyone else. They are just

inquisitive people who use a different

set of tools to ask questions and

formulate answers.

Contents and Selected Applications

Chemical Encounters: Chemists and Their Jobs

1.1 What Do Chemists Do?

1.2 The Chemist’s Shorthand

Chemical Encounters: Desalination

1.3 The Scientiﬁc Method

1.4 Units and Measurement

1.5 Conversions and Dimensional Analysis

1.6 Uncertainty, Precision, Accuracy, and Signiﬁcant Figures

1.7 The Chemical Challenges of the Future

Go to college.hmco.com/pic/kelterMEE for online learning resources.

More than 14,000 students graduate with

chemistry degrees in the United States each year,

according to the American Chemical Society, the

world’s largest professional organization for chemists. Al-

though the majority of these students obtain bachelor’s degrees

(more than 10,000, of which about 50% are earned by women),

many receive advanced degrees (nearly 4,000, of which 40% are earned

by women).What do all of these new chemists do?

As shown in Figure 1.1, about 95,000 chemists are employed across the

country in many sectors of the government, industry, and even academia. Chemists

work with congressional leaders to develop new laws and provide information on

topics of interest to the general public. Chemists design and make new drugs to treat

maladies such as AIDS, attention deﬁcit disorder, and sickle-cell anemia. Chemists

design and manufacture new paints and coatings to keep our lawn chairs and cars

rust-free. Chemists work in the energy industries developing new ways to harness the

power of the Sun. Chemists prepare new laundry detergents that minimize harm to

the environment. Chemists do analyses related to the law, an activity known as

forensic chemistry. These are just some of the many areas where you’ll

ﬁnd chemists at work. As you might also expect, chemists work in the

world’s oil ﬁelds as part of the vital international petroleum industry.

How much do chemists earn? Figure 1.2 shows average salary data

from 2003 to 2004. The average starting salary for chemists entering the

job market in 2003 with a bachelor’s degree was $31,000. For those who

had earned the Ph.D. degree, the average starting salary was $67,500.

More important,the rate of unemployment for the chemistry profes-

sion was only 3.1% nationwide in 2005.When compared to the unemploy-

ment rate of 5% in the United States at large, chemists do fairly well.

In this chapter, we’ll take the ﬁrst steps in learning what it means to

think like a chemist. We will discuss what chemists do. We’ll learn about

the types of questions they ask, and we’ll discover some of the most basic

tools they use to answer those questions.

Application

HEMICAL ENCOUNTERS:

Chemists and

Their Jobs

Pharmaceutical

20%

Federal and state

government

Traditional

chemical

12%

Other

manufacturing

10%

Universities

12%

Biotech

firms

Other

14%

Analytical and

hospital labs

10%

Elementary and

secondary teaching

Chemistry Bachelor's Degrees

Pharmaceutical

29%

Federal and state

government

Traditional

chemical

Other

manufacturing

16%

Universities

19%

Biotech

firms

10%

Other

12%

Chemistry Ph.D. Degrees

Bachelor's

M.S.Ph.D.

2003 2004

Industry $63

$65

Government 58.7 62.4

Academia 36.6 42.2

Industry 76 80

Government 74.5 74

Academia 50.1 52

Industry 100 103

Government 95 98

Academia 65.1 67.2

In thousands of dollars.

FIGURE 1.2

An advanced degree in chemistry boosts

average salary. Employment in industry

is also more lucrative than working in

academia.

FIGURE 1.1

Chemists are employed in many different sectors of the job market.

1.1 What Do Chemists Do?

Judith Fairclough-Baity (Figure 1.3) is an industrial chemist who worked for

19 years at one of the largest chemical companies in the world, where she designed

and made new tubing for heart–lung machines. This tubing carries blood from a

patient undergoing open-heart surgery to a pump and then returns it to the pa-

tient. How did Fairclough-Baity approach her design of these tubes? Just like all

chemists, she deﬁned the key questions for which she

needed answers. The experiments, data analyses, and con-

clusions that are part of this scientiﬁc approach to knowing

led her and her coworkers to a fresh understanding—and

to other questions. Eventually, after extensive experimen-

tation and testing, she and her team arrived at a new

design.

However, it is not just an inquisitive nature that makes

a chemist. Chemists such as Fairclough-Baity also have to

know which questions to ask. This means that chemists

need to have a keen understanding of the basic principles

behind what they do. By knowing the core ideas of this sci-

ence and having a hunger to know, chemists can get to the

bottom of a problem and come up with a possible solu-

tion. For example, questioning chemists discovered Teﬂon (the nonstick coating

on your frying pan), Taxol (a very successful anticancer drug), and the plastic that

makes up squeezable ketchup bottles (Figure 1.4). Their inquisitive approach has

inﬂuenced every aspect of our lives. Today, chemists continue to work on the de-

velopment of countless products, including environmentally friendly alternatives

to gasoline in our cars, faster computer chips, and low-fat potato chips.

1.1 What Do Chemists Do? 3

FIGURE 1.3

Judith Fairclough-Baity worked on

developing new tubing for use in

heart–lung machines.

FFF

FFFFFF

Teflon

High-density polyethylene (HDPE)

“ketchup bottles”

Taxol

FFF

CCCH

OHH

FIGURE 1.4

Teﬂon, Taxol, and ketchup bottles.

Not only do chemists solve problems, but they also share their questions, an-

swers, and discoveries. They effectively communicate with each other via their

common understanding of some fundamental ideas about substances and about

how to make measurements on those substances. We will call this efﬁcient way of

communicating ideas the “chemist’s shorthand.”

1.2 The Chemist’s Shorthand

Chemistry is concerned with the systematic study of the matter of our universe. This

study involves the composition, structure, and properties of matter.

Matter is the

“stuff” of which things are made. Chemists often say that

chemicals make up mat-

ter. Unfortunately, in informal usage, the term chemical is often wrongly applied

only to those materials produced by the chemical industry. In truth, the rainwa-

ter falling into a mountain lake is just as much a chemical as any industrially

produced pesticide that is sprayed onto crops or any of the materials that are

combined to manufacture a plastic soda bottle.

What are some examples of matter? This book is made up of matter. The desk,

your pencil, the coffee in your cup, and the air in your lungs are all examples of

matter. Matter is anything that occupies space and has mass. Then, what isn’t

made up of matter? Energy is not matter in the common sense. Heat and light,

4 Chapter 1 The World of Chemistry

Matter

Environmentally friendly alternatives to gasoline in our cars, faster computer chips, and low-fat

potato chips.

Matter, the stuff of what things are

made, is everywhere.

Video Lesson: An Introduction to

Chemistry

SUBSTANCES

Atoms

Elements

Molecules

Compounds

examples of energy, are not regarded as matter and do not occupy a speciﬁc

volume of space in the conventional sense. On a more complex level, however,

energy and matter are related, as we will learn later.

The chemicals that come together to make matter also occupy space. They,

too, are matter. What makes up chemicals? They are formed from the combina-

tion of inconceivably tiny

atoms, the chemically indivisible particles that chemists

classify by their structure into the more than 90 naturally occurring

elements that

are known in the universe. Chemists and physicists have added to this list by

preparing several additional, large elements that are not found in nature. You will

ﬁnd all the atoms, and therefore all the elements, listed in the periodic table of the

elements on the inside front cover of this book. Many of the elements in the peri-

odic table are familiar because we depend on them in our day-to-day lives. For ex-

ample, the element copper, made from copper atoms, forms the copper wires that

carry electricity around cities and into homes. The ele-

ment helium, made from helium atoms, is the gas that en-

ables weather balloons to rise into the stratosphere. The

element gold, made from gold atoms, is highly prized, es-

pecially when it is encrusted by jewelers with precious

gemstones. The element oxygen is an important part of

the gas we must breathe into our lungs several times each

minute in order to stay alive. However, oxygen gas is not

composed of individual oxygen atoms. Instead, pairs

of oxygen atoms are joined, or bonded, together to form

oxygen molecules. A

molecule, such as the oxygen gas

shown in Figure 1.5, is composed of two or more atoms

bonded together.

Some molecules, such as oxygen, contain identical atoms bonded together.

Nitrogen, the most abundant molecule in the air that you are breathing as you

read this, contains two atoms of the element nitrogen bonded together. However,

many more kinds of molecules can be formed when atoms of different elements

are bonded together.A

compound is matter that contains different elements chem-

ically bonded together. Antoine Lavoisier, a late-eighteenth-century French

chemist,whom we will meet in the next chapter, called a compound any substance

that can be decomposed into two or more other substances.For example,one type

of powdered laundry bleach is a chemical compound composed of the elements

chlorine, oxygen, and sodium. Ethanol, the “active” ingredient in beer, is a com-

pound made up of carbon, hydrogen, and oxygen. Table sugar also has these three

elements, but in different proportions than in ethanol.We call the relative propor-

tions of the elements in a compound its

composition, so we say that the composi-

tion of ethanol is different from that of table sugar.

1.2 The Chemist’s Shorthand 5

HeCu

Molecules

Atoms

Au H

FIGURE 1.5

All of the chemical elements are listed

in the periodic table. Each element is

composed of one kind of atom. Atoms

can become bonded together to form

molecules of elements (such as oxygen)

or molecules of compounds (such as

water).

Physical and Chemical Properties

Often, the chemist doesn’t have access to the composition of a compound. As an

example, assume we have two unlabeled jars. They both contain a

substance,

a type of matter that exhibits a ﬁxed composition.The substance in one of the jars

is called ethanol. The other jar contains the substance we commonly call table

sugar.

How can we tell the difference between the two? If we knew the composi-

tion of each compound, we could determine the answer. The chemist would rely

on asking questions—some difﬁcult, some easy, but all geared toward gathering

the data necessary to solve this problem.

Can we tell the difference between the contents of two jars on the basis of our

observations? Which one is a liquid? Does one have a characteristic odor? An-

swering these questions gives us information about the physical properties of the

compounds. A

physical property is a characteristic of a substance that can be de-

termined without changing its chemical composition. In other words, physical

properties are descriptions of a substance. In our example, the substance ethanol

is a clear and colorless liquid. The table sugar is a solid substance. These are phys-

ical properties of the two compounds. On the basis of these observations, the

chemist could determine which jar is more likely to contain the sugar and which

would contain the ethanol. He or she could even go further by determining the

temperature at which the compounds change from solid to liquid. The melting

point, the temperature at which a substance melts, is an example of a

physical

change

in which the substance changes its physical properties without changing its

chemical composition. For instance, the sugar in the jar changes from a solid to a

liquid at 185°C (365°F). Cellulose has a melting point of 260°C (500°F).

What if we compared a jar of powdered starch to a jar of powdered cellulose

(plant ﬁber)? Figure 1.6 shows what we would see if we examined these com-

pounds up close. Could we use their physical properties to distinguish clearly be-

tween them? At ﬁrst glance they both appear to be powdery solids. Both of these

solids are composed of the same elements. In addition, they appear to have gen-

erally similar physical properties. Their melting points are different, but we might

ask another question to distinguish between these two substances: Do they be-

have in similar ways when combined with other substances? In other words,

they have similar chemical properties?

A chemical property is a characteristic of a substance that can be determined as

it undergoes a change in its chemical composition.Forinstance,the ability of gaso-

line to burn is one its chemical properties.

Chemical changes, the conversion of one

substance into another due to a change in composition or a reorganization of atoms,

often take place in what chemists call

chemical reactions. For example, under the

right conditions, the elements hydrogen and oxygen can react to form water in a

chemical reaction that releases a great deal of energy (see Figure 1.7). This is a

chemical change, because a new chemical, water, forms from the oxygen and hy-

drogen and is a different structural unit. Each water molecule contains one oxygen

atom bonded (chemically joined) to two hydrogen atoms. The formation of water

from hydrogen and oxygen is a very useful chemical reaction in electric-powered

vehicles, because it is accompanied by a release of energy that is used to run such

vehicles. However, it can also be a very dangerous chemical reaction.

Many chemical changes can be both useful and dangerous; the key is to ex-

ploit their utility while avoiding their dangers. One dramatic, but hazardous, use

of the chemical properties of hydrogen and oxygen is to power the main engines

of the space shuttle. Hydrogen and oxygen stored in the shuttle’s main fuel tank

combine explosively, after being ignited, to generate lots of thrust and release a

trail of hot water vapor (Figure 1.8). The newly formed water comes out as a

clear, colorless, hot gas, but it quickly cools and forms the water droplets that

make a thick white “vapor trail” that you see just after the shuttle’s launch.

The dangers of this reaction were tragically demonstrated when the shuttle

6 Chapter 1 The World of Chemistry

FIGURE 1.6

A jar of cellulose and a jar of starch.

Examining physical properties alone may

not be sufﬁcient to identify which of

these jars contains cellulose and which

contains starch.

Application

Video Lesson: Properties of

Matter

Challenger exploded on January 28, 1986. The uncontrolled combination of hy-

drogen and oxygen, initiated by a fault in one of the solid fuel booster rockets, de-

stroyed the spacecraft and killed the entire crew. This, combined with another

deadly explosion upon reentry of the space shuttle Columbia on February 1, 2003,

and funding concerns have placed the future of the shuttle program in doubt.

We now have enough background to answer our question about whether

starch and cellulose have different chemical behavior by looking at our own biol-

ogy. Starch undergoes a chemical change when humans eat it, via the processes

known as digestion and metabolism. Humans, on the other hand, cannot digest

cellulose. Using the physical and chemical properties of these substances, we can

determine which is starch and which is cellulose.

EXERCISE 1.1 Chemical and Physical Changes

Deﬁne each of the following as a chemical or a physical change.

a. Burning automotive fuel in your car

b. Melting ice in a frying pan

c. Dissolving sugar in your tea

d. Digesting the sugar in a chocolate bar

First Thoughts

The key questions are these: What is a physical change? What is a chemical change?

Which of these is represented by each process? Recall that a physical change is one

in which the substance retains its chemical composition (the proportions in which

1.2 The Chemist’s Shorthand 7

FIGURE 1.7

Hydrogen gas and oxygen gas undergo a chemical change to make water. Note that the

composition of water involves a combination of two hydrogen atoms and one oxygen atom.

The chemical change is noted by the evolution of large amounts of heat, light, and sound.

FIGURE 1.8

During a space shuttle launch, the

reaction of the hydrogen and oxygen in

the main fuel tank make a white vapor

trail of water molecules and solid rocket

fuel exhaust that can be seen for miles.