The pH Scale

Is a substance an acid or a base?

Acid Properties

• Donate H+ ions• Taste sour• React with certain

metals to produce hydrogen gas

• React with bases to form salt and water

• Most formulas start with H

• pH < 7What is a hydrogen ion??

What is an ion?

An ion is an atom that has lost or gained an electron giving it a positive (+) or

negative (-) charge.

USES OF ACIDS• Citric acid and ascorbic acid (Vitamin C)

are found in orange juice• Carbonic acid and phosphoric acid give a

“bite” to soft drinks• Acids in your stomach aid in digestion• Sulfuric acid is the most widely used

industrial acid in the world. It is used in making metals, paper, paints, and fertilizers.

Small Intestine

• pH 8, slightly basic

• most chemical digestion completed here

k

BASES• A base is any compound that increases

the number of hydroxide ions (OH-) when mixed with water

• i.e, they are H+ acceptors• A base solution tastes bitter• A base solution feels slippery• A base reacts with acids to form salt

and water• pH > 7

Uses of Bases• Bases are used in soaps

(remember, bases are slippery)• Bases are used to make paper, in

oven cleaners, and to unclog drains• Ammonia is a base and is used in

many household cleaners

Detecting Acids and Bases

• You can detect an acid using an indicator.

• INDICATOR - A substance that changes color in the presence of an acid or a base.

Commonly used indicators

• Indicators are substances that change color in solutions of different pH

• Litmus paper is an indicatorAn acid turns blue litmus paper redA base turns red litmus paper blue

• Cabbage juice can be used as an indicator

phenolphthalein colorless in acid pink in base changes at pH 8.0 -10.0

Indicator

• A compound that changes color when in contact with an acid or a base.

• Bases turn red litmus paper blue.

• Acids turn blue litmus paper red.

bromothymol blue• blue in base• yellow in acid• green in neutral

Which sponge is holding an acid?