acids and bases two special classes of compounds
TRANSCRIPT
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Acids and BasesTwo special classes of compounds
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Elements
• Contain a single kind of atom
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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.
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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.
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Acids and Bases• Acids and bases are special classes of compounds that
exhibit common chemical properties.
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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!
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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
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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.
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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.
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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.
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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
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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.
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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.
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How do we measure the strength of an acid or base?
Use the pH (Powers of Hydrogen) scale
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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
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Lots of H+ = Acid, Lots of OH- = Base.
• What happens if you have a perfect balance of H+ and OH-?• HOH• Or H2O• Water!
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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
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Summary of Characteristics of Acid and Base Compounds
http://www.youtube.com/watch?v=tNvP3-174_M
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Question #1
• Lemon juice has a pH of 2.2. Is it an acid or a base?
• acid
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Question #2
• Detergents such as Tide have a pH of about 10. Is Tide an acid or a base?
• base
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Question #3• Seawater has a pH of 8.2.
Is seawater an acid or a base?
• base
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Question #4• The inside of your mouth
has a pH of 7. Is it an acid or a base?
• neutral
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Question #5• How do you think we came
up with the term “acid rain”?
• Rain water has a pH less than 7
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Question #6• 409 cleaner contains
ammonia that has a pH of 12. What will 409 do to red litmus paper?
• Turn blue
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Question #7• A soft drink has a pH of
3.2. What will it do to a piece of red litmus paper?
• Stay red
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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
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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
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Question #10• What is a physical or
chemical property of water?
• Liquid at room temperature, colorless, has a pH of 7 (is neutral)
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pH of Everyday Substances
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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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