The pH Scale

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The pH Scale

• Is a substance an acid or a base?

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ACIDS

• An acid is a compound that increases the number
  of hydrogen ions when dissolved in water (H)
• An acid solution tastes sour
• An acid can change the color of certain compounds

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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.

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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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BASES

• A base is any compound that increases the number
  of hydroxide ions (OH-) when mixed with water
• A base solution tastes bitter
• A base solution feels slippery
• A base can change the color of certain compounds

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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 indicator
• An acid turns blue litmus paper red
• A base turns red litmus paper blue
• Cabbage juice can be used as an indicator

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HOW DO WE MEASURE pH?
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NEUTRAL
ACID
BASE
0 1 2 3 4 5 6 7 8
9 10 11 12 13 14
The pH Scale
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NEUTRAL
ACID
BASE
0 1 2 3 4 5 6 7 8
9 10 11 12 13 14
The pH Scale
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Lets see what youve learned!

• Professor Know-It-All wants to know what youve
  learned. Answer the following questions
  carefully.

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Question 1

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

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Question 2

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

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Question 3

• Seawater has a pH of 8.2. Is seawater an acid or
  a base?

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Question 4

• The inside of your mouth has a pH of 7. Is it an
  acid or a base?

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Question 5

• How do you think we came up with the term acid
  rain?

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Question 6

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

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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?

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Youve just completed Professor Know-It-Alls Quiz

• Lets see how you did!