Chemical Compounds

WARMUP

Both lemons and tomatoes both contain citric acid,

which gives them a tangy flavor.

Can you think of other foods whose tanginess may be

due to the presence of acids?

CHEMICAL COMPOUNDSPHYSICAL SCIENCE: BOOK L, CHAPTER 3

SECTION 2: ACIDS & BASES

By the end of this section, you should be able to:

• Describe four properties of acids.

• Identify four uses of acids.

• Describe four properties of bases.

• Identify four uses of bases.

ACIDS & THEIR PROPERTIES

• An acid is any compound that increases the number of

hydronium ions, H3O+, when dissolved in water.

• Hydronium ions form when a hydrogen ion, H+, separates

from the acid and bonds with a water molecule, H2O, to

form a hydronium ion, H3O+.

• The sour taste of lemons, limes, and other citrus fruits is a

result of citric acid.


• Taste, touch, or smell should NEVER be used to identify an

unknown chemical. Many acids are corrosive, which means

that they destroy body tissue, clothing, and many other

things.

• Most acids are also poisonous.


• A substance that changes color in the presence of an acid or

base is an indicator.

• This flask contains water and an indicator called bromthymol

blue.


• When acid is added, the color changes from pale blue to

yellow because of the presence of the indicator.


• Another common indicator used in the lab is litmus. Paper

strips containing litmus change color when acid is added.


• Acids react with some metals to produce hydrogen gas.

When hydrochloric acid reacts with zinc metal, hydrogen gas

is formed.

• This is the equation:

2HCl + Zn H2 + ZnCl2


• In the reaction, zinc displaces hydrogen in the compound,

hydrochloric acid. This displacement happens because zinc is

an active metal.

• If silver were put into hydrochloric acid, no reaction would

take place because silver is not an active metal.


• When acids are dissolved in water, they break apart and

form ions in the solution. The ions make it possible for the

solution to conduct an electric current.

• A car battery is one example of how an acid can be used to

produce an electric current. The sulfuric acid in the battery

conducts electricity to help start the car’s engine.

USES OF ACIDS

• Sulfuric acid is the most widely made industrial chemical in

the world. It is used to make paper, paint, detergents,

fertilizers and many other products.

• Nitric acid is used to make fertilizers, rubber, and plastics.

USES OF ACIDS

• Hydrochloric acid is used to make metal from their ores by

separating the metals from the material with which they are

combined.

• Hydrochloric acid is used in swimming pools to help keep

them free of algae. Hydrochloric acid is even found in your

stomach, where it aids in digestion.

USES OF ACIDS

• Citric acid and ascorbic acid (vitamin C) are found in orange

juice.

• Carbonic acid and phosphoric acid help give soft drinks a

sharp taste.

BASES AND THEIR PROPERTIES

• A base is any compound that increases the number of

hydroxide ions, OH-, when dissolved in water.

• For example, sodium hydroxide breaks apart to form sodium

ions and hydroxide ions, as shown in this formula:

NaOH Na+ + OH-


Hydroxide ions give bases their properties. Some examples

of bases include soaps, ammonia, baking soda, bleach, and

detergents.

If you have ever tasted soap, you know the bitter taste of a

base. Soap will also have the slippery feel of a base.


• Taste, touch, or smell should NEVER be used to identify an

unknown chemical. Like acids, many bases are corrosive.

• Like acids, bases change the color of an indicator. Most

indicators turn a different color in the presence of bases

than they do in the presence of acids.


• For example, bases change the color of red litmus paper to

blue.

• When a base is added to bromthymol blue, it turns the

indicator from pale blue to dark blue.


• Solutions of bases conduct electricity because bases increase

the number of hydroxide ions, OH-, in a solution.

• A hydroxide ion is actually a hydrogen atom and an oxygen

atom bonded together. The extra electron gives the

hydroxide ion a negative charge.

USES OF BASES

• Sodium hydroxide is a base used to make soap and paper. It

is also used in oven cleaners and products that unclog

drains.

• Calcium hydroxide, Ca(OH)2, is used to make cement and

plaster.

USES OF BASES

• Ammonia is found in many household cleaners and is used

to make fertilizers. Magnesium hydroxide and aluminum

hydroxide are used in antacids.

SECTION 2 REVIEW

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WARMUP

Write down as many acids and bases as you can

think of without looking at your notes.

SECTION 3: SOLUTIONS OF ACIDS & BASES

By the end of this section, you should be able to:

• Explain the difference between strong acids and bases and

weak acids and bases.

• Identify acids and bases by using the pH scale.

• Describe the formation and uses of salts.

STRENGTHS OF ACIDS & BASES

• Acids and bases can be strong or weak. Strength of an acid

or a base is not the same as the concentration of an acid or

a base.

• The concentration of an acid or a base is the amount of

acid or base dissolved in water.

STRENGTHS OF ACIDS & BASES

• The strength of an acid or a base depends on the number of

molecules that break apart when the acid or base is

dissolved in water.

STRONG VERSUS WEAK ACIDS

• As an acid dissolves in water, the acid’s molecules break

apart and produce hydrogen ions, H+.

• If all the molecules break apart, the acid is called a strong

acid. Strong acids include sulfuric acid, nitric acid, and

hydrochloric acid.

STRONG VERSUS WEAK ACIDS

• If only a few molecules break apart, the acid is a weak acid.

Weak acids include acetic acid, citric acid, and carbonic acid.

STRONG VERSUS WEAK BASES

• When all molecules of a base break apart in water to

produce hydroxide ions, OH-, the base is a strong base.

• Strong bases include sodium hydroxide, calcium hydroxide,

and potassium hydroxide.

STRONG VERSUS WEAK BASES

• When only a few molecules of a base break apart, the base

is a weak base, such as ammonium hydroxide and aluminum

hydroxide.

ACIDS, BASES, & NEUTRALIZATION

• The reaction between acids and bases is called a

neutralization reaction.

• Acids and bases neutralize one another because the

hydrogen ions (H+) in an acid and the hydroxide ions (OH-)

in a base react to form water, H2O.


• Other ions from the acid and base dissolve in the water. If

the water evaporates, these ions join to form the compound

called a salt.

• An indicator, such as litmus, can identify whether a solution

contains an acid or base.


• To describe how acidic or basic a solution is, the pH scale is

used. The pH of a solution is a measure of the hydronium

ion concentration in the solution.

• A combination of indicators can be used to find out how

basic or how acidic a solution is. This can be done if the

colors of the indicators are known at different pH values.


• This picture shows strips of pH paper, which contains several

different indicators.


• Living things depend on having a steady pH in their

environment.

• Some plants prefer acidic soil with a pH between 4 and 6.

Other plants need basic soil with a pH between 8 and 9.

• Many organism living in lakes and streams need a neutral

pH to survive.

SALTS

• When an acid neutralizes a base, a salt and water are

produced. A salt is an ionic compound formed from the

positive ion of a base and the negative ion of an acid.

• Sodium chloride, commonly known as table salt, is one

example of a large group of compounds called salts.

SALTS

• Sodium chloride is used to season foods. It is also used to

make other compounds, including lye (sodium hydroxide)

and baking soda.

SALTS

• Sodium nitrate is a salt that is used to preserve foods.

Calcium sulfate is used to make materials used in

construction.

• In some regions, salt is used to keep roads free of ice by

decreasing the freezing point of water.

SECTION 3 REVIEW

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Chemical Compounds

Education

Transcript of Chemical Compounds