acids and bases two special classes of compounds

Acids and BasesTwo special classes of compounds

Elements

• Contain a single kind of atom

Compounds• Substances that are chemically formed• They have physical and chemical properties that are different

from the elements that make them up.• They are formed as the result of a chemical reaction.

Hydrogen (an explosive gas) and oxygen (an explosive gas) combine to form the compound water (a harmless liquid).

Here, the hydrogen gas in the zeppelin SS Hindenburg reacts with oxygen in the air to make water.

Source: Photo courtesy of the US Navy, http://commons.wikimedia.org/wiki/File:Hindenburg_burning.jpg.

Acids and Bases• Acids and bases are special classes of compounds that

exhibit common chemical properties.

Acids and Bases• Acids and Bases can be helpful or harmful.• Acids and bases can be weak, some or strong.• YOU MUST ALWAYS BE CAREFUL WHEN WORKING

WITH ANY CHEMICALS!

Characteristics of Acids

• Have a sour taste• They have Hydrogen atoms which

have given up their electron, making them positive ions. (H+)

• They turn blue litmus paper red• They react with metals to release

Hydrogen gas. http://www.youtube.com/watch?v=PqUOGc6P05c

What is an ion?An ion is an atom that has lost or gained an electron giving it a

positive (+) or negative (-) charge.

3 protons (+) and 3 electrons (-) = neutral charge

Atoms don’t like having a non full outer shell, so this atom will give

away its one valence electron making it 3+ and 2- for an overall

1+ charge, making it a positive ion.

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.

Characteristics of Bases• Have a bitter taste (never taste an

unknown!)• They feel slippery• They have Hydroxide (OH)

compounds which have taken on an electron, making them negative ions. (OH-)

• They turn red litmus paper blue• They do not react with metals.

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.

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

• Universal test papers can identify acids and bases

• Cabbage juice can also be used as an indicator. The juice should turn pink in acidic solutions, and green/blue/yellow in basic solutions.

How do we measure the strength of an acid or base?

Use the pH (Powers of Hydrogen) scale

pH scale

• Acids and Bases are ranked on a pH scale.

• 0-6.9 = acids, lots of H+ ions

• 7.1-14 = bases, lots of OH- ions

Lots of H+ = Acid, Lots of OH- = Base.

• What happens if you have a perfect balance of H+ and OH-?• HOH• Or H2O• Water!

Pure Water (H2O) is a perfect balance of the H+ ions and OH- ions• Pure water is a 7 on the pH scale, it is called Neutral

Common products and pH range

Summary of Characteristics of Acid and Base Compounds

http://www.youtube.com/watch?v=tNvP3-174_M

Question #1

• Lemon juice has a pH of 2.2. Is it an acid or a base?

• acid

Question #2

• Detergents such as Tide have a pH of about 10. Is Tide an acid or a base?

• base

Question #3• Seawater has a pH of 8.2.

Is seawater an acid or a base?

• base

Question #4• The inside of your mouth

has a pH of 7. Is it an acid or a base?

• neutral

Question #5• How do you think we came

up with the term “acid rain”?

• Rain water has a pH less than 7

Question #6• 409 cleaner contains

ammonia that has a pH of 12. What will 409 do to red litmus paper?

• Turn blue

Question #7• A soft drink has a pH of

3.2. What will it do to a piece of red litmus paper?

• Stay red

Question #8• What is a physical or

chemical property of an acid?

• Tastes sour, has a pH below 7, turns litmus paper red, produces H+ ions

Question #9• What is a physical or

chemical property of a base?

• Tastes bitter, feels slippery, has a pH above 7, turns litmus paper blue, produces OH- ions

Question #10• What is a physical or

chemical property of water?

• Liquid at room temperature, colorless, has a pH of 7 (is neutral)

pH of Everyday Substances

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Practice Acid/Base experiments

http://www.kidsknowit.com/interactive-educational-movies/free-online-movies.php?movie=Acids%20And%20Bases

http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks3/science/acids/

http://www.youtube.com/watch?v=ujkuW-0cpNwMagic tricks with Acids and Bases