Acids and Bases

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Acids and Bases
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Acids

• Acids are substances that release hydrogen ions,
  H, in solution
• Acids can be recognized because their chemical
  formulas start with the symbol for hydrogen, H
• HCl hydrochloric acid
• H2SO4 sulfuric acid
• HNO3 nitric acid

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Bases

• Bases are substances that release hydroxide ions,
  OH-, in solution
• Many bases can be recognized because their
  chemical formulas end with OH
• NaOH sodium hydroxide
• Ca(OH)2 Calcium hydroxide

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Bases

• A base can also be called an alkali
• Remember the alkali metals which group?
• Combine with hydroxide to form the strongest bases

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The pH Scale

• Used to show the strength of an acidic or basic
  solution
• Measures the concentration of H ions in solution
• An acid has a pHlt7
• A base has a pHgt7
• Pure water has pH7 (the concentrations of H and
  OH- ions are equal)

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The pH Scale

• pH can be determined by using
• Indicators (such as phenolphthalein)
• Litmus and pH papers (contain chemicals that turn
  certain colors in the presence of acids or bases)
• pH meter

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The pH Scale

• The concentration of H ions is inversely
  proportional to the concentration of OH- ions
• As the concentration of H ions increases, the
  concentration of OH- ions decreases
• As the concentration of OH- ions increases, the
  concentration of H ions decreases

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pH of Household Chemicals

• You might be surprised to know that many
  household items are acids and bases.
• We can use litmus paper and indicator to find out
  which are acids and which are bases.

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Conductivity

• Solutions that conduct electricity are called
  electrolytes
• In order to conduct electricity, there must be
  charged particles in the solution
• Which things will conduct electricity?
• Water Salt
• Sugar Baking soda
• Vinegar

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Conductivity

• Solutions that conduct electricity are called
  electrolytes
• In order to conduct electricity, there must be
  charged particles in the solution
• Which things will conduct electricity?
• Salt
• Sugar
• Acids and bases both conduct electricity because
  they form ions in solutions

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Other Properties

• Acids are corrosive, bases are caustic (both can
  cause burns)
• Acids taste sour (think lemon juice or vinegar)
• Bases taste bitter (ever tried plain baking
  soda?)
• Bases feel slippery because they react with the
  fats in your skin to make soap

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Neutralization Reactions

• Acids and bases combine to form a salt and water
• This is called neutralization and is a double
  replacement reaction
• HCl NaOH ? NaCl H2O
• acid base salt water
• When the reaction is complete, the pH will be 7,
  or neutral