Download Acids and Bases


You go to a grocery store to purchase lemons, milk,
tomatoes, and soap.

Have you purchased any items that are acidic, neutral, or
basic?

An indicator will help determine which category various
items fit into.
Acids

Acids are compounds that release hydrogen ions (H+) when
placed in water. The more hydrogen ions that are released,
the greater the acidity of the compound.

Examples of strong acids: Hydrochloric acid, and Sulfuric
acid.

Examples of weak acids: Vinegar, and acetylsalicylic
(aspirin).

Acids tend to be sour in taste and are readily soluble in
water.

It is important for gardeners to know the chemical nature of
the soil. They buy fertilizers that supplement soil
deficiencies. Acidic soil requires fertilizer containing potash
to make it less acidic.

Manufacturers of car batteries use sulfuric acid to provide
the reaction required for producing an electrical current.

Stomach acid help breakdown food protein into form that
can be absorbed into the blood stream.
Bases

Bases are compounds that release hydroxyl ions (OH-) into
water.

Bases are slippery to the touch, bitter in taste, and soluble
in water.

Bases are important in our lives.

Baking soda makes cakes and bread rise.

Soaps and shampoos are used for cleaning.
Indicators

An indicator is a chemical substance, usually obtained from
plant material that changes color in the presence of an acid
or base.

The most common indicator is called the universal
indicator.

It comes as a special bottled solution or paper dipped in this
solution (pH paper).

Several other types of acid-base indicators include litmus
and red cabbage juice.
Indicator Examples

Litmus paper demonstration

Bromothymol blue demonstration

Rainbow Connection demonstration

The universal indicator changes to different colors in
different substances. The color is compared to a pH scale
and pH number of the substance is determined.
The pH Scale

The pH scale is designed to indicate the concentration of
hydrogen ions in a solution.

A pH scale ranges from 0 to 14.

Acids fall in a range from 0 to 6, neutral substances are 7,
and bases range from 8 to 14.

A pH test paper is dipped into a solution and the color
produced is compared with a commercial color scale.

A reddish color indicates a pH of 1, green indicates pH of 7,
and blue indicates pH of 14.

Common Substances and their pH: (Note p. 198)






Battery acid pH 0.7
Stomach acid pH 1.0
Lemon Juice pH 2.0
Distilled water pH 7.0
Baking soda pH 8.0
Drain cleaner pH 13.5

A substance with pH 1 is a strong acid whereas a substance
with pH 5 is a weak acid.

A substance with pH 8 is a weak base whereas a substance
with a pH of 14 is a strong base.

As the pH of a substance increases or decreases, the acid
concentration increases or decreases.

Every number on the pH scale represents a difference in
concentration by a factor of 10. A pH reading of 4 is 100
times more acidic than a pH of 6. Similarly, a pH of 11 is
1000 times more basic than a pH of 8
Neutralization

Strong acids and strong bases are corrosive and can be
dangerous if not handled properly.

Should the need arise, a strong acid can be neutralized with
a strong base.

The process of neutralization involves mixing an acid with
a base to produce salt (ionic compound) and water.
Acid
+
Base

Salt
+
Water

Antacids, like Alka-Seltzer, are taken for stomach acidity.

When taken, an antacids starts a neutralization reaction.

The acid is converted to a type of salt.