Acids%20and%20Bases

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Acids and Bases

• Chapter 32

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What are Acids?

• Acids are common chemicals, some of which are
  corrosive and dangerous and some of which are
  quiet harmless.

Strong acids Hydrochloric Acid(HCl) Sulfuric
Acid(H2SO4)
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Some common Acids
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Bases(or alkalis)

• Bases are opposite to acids
• Bases soluble in water are called alkalis.
• Alkalis have a soapy feel.
• Examples of bases
• Sodium Hydroxide NaOH
• Calcium Hydroxide Ca(OH)2

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Indicators

• An indicator shows by means of a colour change
  whether a substance is an acid or a base.
• Acid turns Litmus from blue to red
• Bases turn litmus from red to blue

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The pH scale

• Litmus can only tell if a substance is an acid or
  base. It cannot tell the different strength of
  Acids or Bases.
• The pH scale indicates the level of acidity or
  basicity in a solution.
• A solution that has a pH of 7 is neutral
• A solution that has a pH less than 7 is acidic
• A solution that has a pH greater than 7 is
  alkaline.

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pH scale
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Universal Indicator

• Universal Indicator can be used to find the exact
  pH of a substance.
• Universal indicator paper changes to a different
  colour depending on the pH of the solution.

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Reactions of Acids

• Acids are involved in the following reactions.
• Acid Base --gt Salt water
• Acid Carbonate --gt Salt Water Carbon
  Dioxide
• A salt is formed when the Hydrogen of an
• acid is replaced by a metal.

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Acid Base

• An acid and an alkali neutralise each other in a
  neutralisation reaction.
• Hydrochloric acid and Sodium hydroxide react
  together to form sodium chloride and water.
• HCL NaOH --gt NaCL H2O

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To Neutralise an Acid and a Base by Titration
Step 1. Using a pipette,place 20 ml of Sodium
Hydroxide into a conical flask and a few drops of
litmus indicator. Step 2. Fill the burette to
the top mark with Hydrochloric acid. Step 3.
Adjust level of meniscus of HCl in the burette to
zero mark.
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Step 4. Place the conical flask on a white
tile Step 5. Start adding the acid to the
base Step 6. The acid is added slowly until one
drop turns the solution pink.
When the indicator has changed colour, stop the
titration and note the volume of acid added.
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• Step 7. Repeat the experiment but do not use
  indicator.
• Step 8. The sodium chloride is put in an
  evaporation dish.
• Step 9.The solution is evaporated to dryness and
  then left to cool
• Step 10.A white crystalline substance is formed
  and sodium chloride has been formed.