5 2 acids and bases at work (physical sciences)

California Leveled Science Readers (Grade 5) Content leveled readers teach science concepts, vocabulary, and reading skills – at each student’s reading level – and allow students to read and explore the wonders of nonfiction. Leveled science readers deliver science content to help address the individual needs of all students. They reinforce reading skills and strategies while promoting science understanding. Each grade 5 science reader is a richly illustrated, selfcontained little book with 10 to 14 double pages. BELOW 5.1 Building Blocks of Matter (Physical Sciences) 5.2 Changes in Matter (Physical Sciences) 5.3 Basic Structures of Organisms (Life Sciences) 5.4 MISSING 5.5 Water on Earth (Earth Sciences) 5.6 Weather (Earth Sciences) 5.7 The Solar System (Earth Sciences) ON 5.1 Understanding Matter (Physical Sciences) 5.2 How Matter Changes (Physical Sciences) 5.3 The Building Blocks of Organisms (Life Sciences) 5.4 Systems of the Human Body (Life Sciences) 5.5 Earths Hydrosphere (Earth Sciences) 5.6 How Weather Works (Earth Sciences) 5.7 Earths Solar System (Earth Sciences) ADVANCED 5.1 Atoms (Physical Sciences) 5.2 Acids and Bases at Work (Physical Sciences) 5.3 MISSING 5.4 MISSING 5.5 MISSING 5.6 Hurricanes (Earth Sciences) 5.7 The Red Planet (Earth Sciences)

Genre Comprehension Skill Text Features Science Content

Nonfi ction Draw Conclusions • Captions

• Diagram

• Labels

• Glossary

Matter

Scott Foresman Science 5.2

ISBN 0-328-23568-7

Physical Sciences

chemical change

chemical equation

condensation

evaporation

physical change

product

reactant

sublimation

Extended Vocabulary

corrosive distilled neutralization

pH scale solute solvent

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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

by Donna J Watson

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 defi nite shape and volume Liquids have defi nite volume but

take the shape of their container Gases have neither a defi nite

volume nor shape They expand to fi ll 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 fi rst becoming

a liquid, this is called sublimation

3

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 identifi cation 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.

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 fi ght 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

Acids and bases are found

in common things.

5

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

Alchemists experimented with chemicals.

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

The work of several

scientists helped lead

to the discovery of

acids and bases.

Robert Boyle 1660s

7

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 defi nitions 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 defi nition at the same time Today it is called the Bronsted-Lowry defi nition It explains why acids and bases behave the way that they do

Svante Arrhenius early 1900s

Antoine Lavoisier 1770s

7

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

• neutralize bases in a neutralization

reaction

• corrode metals

• turn blue litmus (indicator paper)

to red

• have a sour taste

Bases

• 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.

9

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 classifi ed 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

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 fi nd 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.

11

Vitamin C is an acid found

in orange juice.

Antacids like these help relieve your stomach if it has too much acid.

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

Food

Another place we fi nd 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

Some foods, such as citrus fruits, are naturally acidic

Other foods, such as pickles, are prepared with acids.

13

Baking

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 “fl uffy” 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.

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 fi nd 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

Early soap factories used soda ash to make soap.

15

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 fi elds 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 artifi cial 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

Acids are used to create a variety of fabric dyes.

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 fi nish 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!

car battery galvanized can

Chemical Warning Labels

Harmful or Irritating

Poisonous

Corrosive

Flammable

Explosive

Radioactive

17

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 earlier that attempts to make soda ash artifi cially led to pollution Problems with pollution from strong acids and bases continue today