5 2 acids and bases at work (physical sciences)

Physical Sciences

Genre

Nonfiction

Comprehension Skill

Draw Conclusions

Text Features

•
•
•
•

Captions
Diagram
Labels
Glossary

Science Content

Matter

Scott Foresman Science 5.2

ISBN 0-328-23568-7

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by Donna J. Watson


Vocabulary

Extended Vocabulary

chemical change
chemical equation
condensation
evaporation
physical change
product
reactant
sublimation

corrosive
distilled
neutralization
pH scale
solute
solvent

by Donna J. Watson

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ISBN: 0-328- 23568-7
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1 2 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06


What You Already Know
Matter changes all the time. Some changes are physical
changes in position, size, shape, volume, or phase of matter.
Other changes are chemical changes. Chemical changes occur
when one type of matter changes into a different kind of matter
with different physical properties.
Matter has three states: solid, liquid, and gas. Solids have
a definite shape and volume. Liquids have definite volume but
take the shape of their container. Gases have neither a definite
volume nor shape. They expand to fill their container.
Physical properties of matter
include freezing, melting, and boiling
points. When a liquid substance is
heated enough, the particles move

faster and eventually the liquid
becomes a gas. This process is called
evaporation. When a gas touches a
cold surface, its particles slow down
and become liquid again. This is called
condensation. If the particles in a solid
escape as a gas without first becoming
a liquid, this is called sublimation.

During a chemical reaction, a chemical change takes
place. This reaction usually involves at least two elements or
compounds. Any substance involved in a chemical reaction is
called a reactant. Any substance made by a reaction is called a
product. The physical and chemical properties of the products
differ from those of the reactants. Reactions can be written as a
chemical equation. In chemical reactions, matter is never created
or destroyed. This is called the Law of Conservation of Mass.
Understanding chemical and physical properties of
substances can be helpful for
the identification of those
substances.
In this book you will
learn more about acids and
bases, their physical and
chemical properties, and
their uses.

Rust is a chemical property of iron.

2

3


History of Acids
and Bases
Acids and bases are amazing substances that have an effect
on your daily life! Acids and bases are found in food and drink,
machines, and cleaning products. They work inside your body
to process food and fight disease. As you will see, acids and
bases help us in many ways, even though some can be harmful
to people and the environment.
Before we look at how acids and bases are used, let’s learn
something about their properties and how they were discovered.
Alchemists experimented with chemicals.
Acids and bases are found
in common things.

4

People were using acids and bases long before they
understood them. Foods were aged creating a sour taste.
Something that tasted sour was referred to as oxein in Greek
and acere in Latin, which means “to make sour.” Our word
“acid” comes from this. Over time, people discovered that
things that tasted sour shared similar properties. It was not until
more recently that the chemistry behind acids and bases was
understood.
As early as the middle ages, alchemists, scientists who tested
chemicals and metals, were experimenting with substances that

had acidic qualities. They found that some acid mixtures could
dissolve elements such as gold. As a result, they didn’t have to
use heat or wait a long time to break down a substance. By the
1600s, chemists and doctors were spending more time studying
chemical reactions between acids and bases.

5


During the 1660s, a European scientist named Robert Boyle
started to record some chemical properties of acids and bases.
To help identify which materials were acids and which were
bases, he developed the use of litmus, or indicator, paper. Litmus
is a substance found in plants. Boyle observed that matter having
acidic qualities turned litmus paper red. He also observed that
matter having basic qualities turned litmus paper blue.
One hundred years later, a French scientist named Antoine
Lavoisier did more experiments on water and air. He discovered
that water is made of two different substances. He named the
two substances hydrogen and oxygen. At the time, he thought
oxygen was an ingredient in every acid. So the word oxygen
comes from the Greek for “acid-former.”
Although Lavoisier correctly determined the two
components of water, he was wrong about acids. Oxygen is
in many acids, but not all. Even so,
his work was a building block
for other scientists studying
acids and bases.

In the 1800s and early 1900s, scientists all over the world

continued to study acids and bases. A Swedish scientist named
Svante Arrhenius tried to explain the chemical reaction that occurs
between acids and bases. He thought that when the molecules of
acids and bases broke apart, they released different particles. He
used this to come up with definitions for acids and bases.
By the early 1920s, two scientists, Johannes Bronsted from
Denmark and Thomas Lowry from England, improved on
Arrhenius’s ideas. Although they were not working together,
they proposed the same definition at the same time. Today it is
called the Bronsted-Lowry definition. It explains why acids and
bases behave the way that they do.

The work of several
scientists helped lead
to the discovery of
acids and bases.

Robert Boyle
1660s

6

Antoine Lavoisier
1770s

Svante Arrhenius
early 1900s

77

Properties and the
pH Scale
Over the centuries, the work of many scientists has provided
us with the properties of acids and bases. They discovered that
acids and bases have properties that are opposite to one another.

Acids

Bases

• neutralize bases in a neutralization
reaction
• corrode metals
• turn blue litmus (indicator paper)
to red
• have a sour taste

• neutralize acids in a neutralization
reaction
• have a slippery feeling
• turn red litmus (indicator paper) to
blue
• have a bitter taste

Acids and bases are tested with special papers
and solutions. Never test acids and bases by
putting unknown things in your mouth.
lemon juice

8

tomato juice

As scientists studied more about acids and bases, one thing
they learned was that adding an acid to a base made the base
weaker. The opposite is also true. This is called neutralization.
If acids and bases can be made weaker by adding one to
the other, then both acids and bases can be classified as strong
or weak. How do you determine the strength or weakness of
an acid or a base? Acids and bases are measured by something
called the pH scale. This name stands for “power of hydrogen.”
The pH scale ranges from 0 to 14. The strength of an acid is
measured between 0 and 7. Strong acids are closer to 0 on the
scale. Bases have a pH between 7 and 14. Strong bases are closer
to 14 on the scale. A substance with a pH of 7 is considered
neutral and is represented by distilled water.
When a strong acid and a strong base mix, there can be
a surprising result. If one of the strongest acids, hydrochloric
acid (pH = 0), is mixed with one of the strongest
bases, sodium hydroxide (pH = 14), the two
will neutralize each other. A chemical
reaction will take place resulting
in two very different substances.
In this case, the result is water
and ordinary table salt. In fact,
whenever acids and bases form a
solution, the result is water and
a salt. There are many kinds of
salts, although the most familiar

one to us is table salt.

seawater

household ammonia

9


Using Acids and Bases
Now that you know a little bit about the history and the
characteristics of acids and bases, you might ask, “Why are
people so curious about acids and bases?” and “How are they
important to us?”

The Body
One of the most interesting places we find acids and bases
is in the human body. The cells of the body contain weak acids
and bases. For instance, human blood has a slightly basic pH of
7.35 to 7.45. But the skin on the human body is slightly acidic.
This protects the body from bacteria and viruses. The pH levels
of all body cells need to remain fairly constant to prevent a fatal
reaction. The body has built-in safeguards to protect against
extreme swings in the pH levels of its cells.
Acids and bases become more useful
as we learn more about them.

The body also uses acids and bases in the digestive system.
As soon as food enters the mouth, saliva, which contains a mild
acid, starts the process of digestion. The food quickly reaches the

stomach where stomach acid (pH = 1) breaks down the food for
use by the body.
You may have some common acids and bases in your home
that you take to keep your body healthy. Did you know that
aspirin and vitamin C are acids? If the body produces too much
stomach acid, it can cause discomfort. The common treatment
for excess acid in the stomach is to take a medicine called an
antacid. Antacids counteract, or neutralize, acidity.

Vitamin C is an acid found
in orange juice.
Antacids like these help
relieve your stomach if it
has too much acid.

10

11


Baking

Some foods, such as citrus
fruits, are naturally acidic.
Other foods, such as pickles,
are prepared with acids.

Food
Another place we find lots of acids is in food. Citrus
fruits—lemons, limes, grapefruits, and oranges—contain citric

acid. Vinegar is a solution of water and acetic acid. Foods that
contain vinegar, such as pickles and some salad dressings, have
acetic acid. Sour cream, yogurt, and cottage cheese contain
lactic acid. Soft drinks contain a number of different acids,
which can be harmful to teeth. All of these foods taste a little
sour—one of the physical properties of acids.
Some sour foods are too strong, or too acidic, to use
the way they are. In order to make it easier to use
these foods, water can be added to make a solution.
For instance, water can be added to lemon juice to
make it less sour. This solution has two parts. The
lemon juice is referred to as the solute. When it
is dissolved in another substance, the solvent, it
makes a new solution.

12

You have read a lot about foods that are acidic. Do any
foods contain bases? Egg whites are slightly basic. Bases are
used in baking because of the chemical reactions they cause.
For example, sodium bicarbonate, commonly called baking
soda, is a base that is often an ingredient in baking recipes.
When a basic ingredient comes into contact with an acidic
ingredient, such as buttermilk, molasses, or lemon juice,
a reaction occurs. The reaction between the acid and the
base creates bubbles of carbon dioxide. The carbon dioxide
makes baked goods rise. As the CO2 escapes from the
dough, it creates the little holes found in breads and cakes,
giving them their “fluffy” texture and appearance.
Baking powder is another ingredient used to make

dough rise. Baking powder is a mixture of an acid and a
base. When it gets wet the acid and base react and start
releasing carbon dioxide.
Basic ingredients help
give soda bread its
shape and texture.

13


Early Industry
Acids and bases are not just found in your home. They have
been used by industries for hundreds of years. In the 1700s and
1800s, factory owners and scientists knew about the importance
of soda ash, or sodium carbonate. It is a base that was used to
manufacture soap, glass, paper, bleaches, and dyes. Soda ash
was removed from sea kelp or made from an imported material
called potash. These were expensive and time-consuming
methods. Chemists tried to find new, cheaper ways to make
soda ash. They succeeded, but all the new ways polluted the soil
and air. In fact, most of the new methods involved a strong acid
known as sulfuric acid, which created breathing problems for
factory workers.
Acids are used to create a variety of fabric dyes.
Early soap factories used soda ash to make soap.

Another early industrial use of acids and bases was in
the creation of bleaches and dyes for the fabric industry in
England. Sour milk (an acid) and ammonia (a base) were used
to bleach, or whiten, fabrics. Other times, fabrics were spread

out in large fields of grass to be whitened by the Sun. Both of
these processes took a long time to turn the fabrics white. A
new method was tried where chlorine was passed over a base
material of crumbled lime to neutralize it, creating a bleach
whitener. This new process made the manufacturing of fabrics
much faster.
By the mid-1860s, chemists were just starting to make
artificial dyes from acids. For instance, mixing together two
different acids created a new purple dye. Only natural dyes from
plants, berries, and other raw materials had been used before the
discovery of this new method.

14

15


Modern Industry
A more modern use of acids and bases is in machinery. Most
vehicles with a gasoline engine need a battery to produce a
spark. Those batteries all contain battery acid (pH = 1). Another
use of acids is for polishing metals. Acids can eat away, or
corrode, metals. If the acids are used in small amounts and with
the proper tools, they can put a nice finish on metals. Maybe
you have seen the name of a business or a decorative design cut
into a glass door or window. You may be surprised to know that
acids are used to etch, or cut, those designs into the glass!

Bases are still used in the dyeing and bleaching of fabrics.
Some common bases include ammonia for cleaners, fertilizers,

and rayon and nylon fabrics. Sodium hydroxide (the strongest
base) is also known as lye. It is used in soaps, oven and drain
cleaners, and paper and food manufacturing.
Most of the acids and bases you have read about are very
valuable for industry, your body, or food production. Sometimes
acids and bases can also
cause damage. You read
Chemical Warning Labels
earlier that attempts to make
soda ash artificially led to
pollution. Problems with
Harmful or
pollution from strong acids
Irritating
and bases continue today.
Poisonous

Corrosive

Flammable

Explosive

Radioactive

galvanized can

16

car battery

17


Pollution
You may have heard of acid rain. This is a term that refers
to precipitation that has a lot of acid in it. Some acid is normal
in rain, but scientists have learned that human activities have
increased its amount. Some factories and power plants burn fuel
that releases certain sulfur and nitrogen gases. These gases can
combine with water in the air to produce acids.
Acid rain falls as precipitation in the form of rain, fog, or
snow. The water carries high levels of acid that pollute the
environment. When acid rain falls on rivers and lakes, it can
be strong enough to kill fish and other living things. It can
damage crops, forests, and even the soil. Acid rain also corrodes
buildings made of limestone, marble, and metal.
1

Factories release gases into the
air. Wind carries the gases.

2

Protection from Acids
and Bases
Communities and businesses are trying to reduce acid rain.
People are using fuels that cause less pollution. There are also
limits on how much a company can pollute. Since electric
power plants release gases that cause acid rain, individuals can

help by saving power. They can turn off lights, televisions, and
computers when they aren’t being used.
Besides being able to damage buildings, the burning of
certain fuels in cars or in factories can create smoke and fumes
that are harmful to breathe. Many cities that have trouble with
this sometimes warn residents to stay inside because of problems
with the air. It is also important to keep strong acids and bases
from touching a person’s skin because they can cause burns.
Protective clothing, including gloves, boots, and eyewear, must
be worn around strong chemicals.
Acids and bases need to be used
cautiously because of the damage
they can do, but they also should be
appreciated for their many different
uses in all aspects of our world!

These gases combine
with moisture.

3

18

The result is acid rain that
falls on land and water.

19


Glossary

What did you learn?
1. What are some uses of bases?

corrosive

to slowly weaken and destroy

distilled

purified

3. Why is acid rain a problem?

neutralization

in chemistry, the process of mixing acids and
bases so they counter each other’s properties

4.

pH scale

a system for measuring the strength of acids
and bases, where lower numbers indicate
increasing acidity, higher numbers indicate
increasing alkalinity, and 7 represents
neutrality

In this book you learned about the history

of acids and bases. Write a research report exploring the work of a
scientist that you read about. Ask yourself what you want to learn
about the scientist, and then develop a topic using those ideas.

5.

Draw Conclusions You read that when an acid and a base are
mixed they neutralize each other. Sometimes, mixing an acid and a
base of different strengths results in a product that is acidic or
basic. Using what you know about the pH scale, determine
whether the product of the following reactions would be acidic,
basic, or neutral: hydrochloric acid (pH = 0) and sodium hydroxide
(pH = 14); vinegar (pH = 3) and ammonia (pH = 11); and baking
soda (pH = 9) and lemon juice (pH = 2).

solute

the substance that dissolves into a solution

solvent

the substance in a solution in which the
solute dissolves

20

2. How do bases work in baking?