Acids Bases and Salts

==Acid and Base/Alkali Reactions==

• Acid + Metal → salt + hydrogen

  • Sulphuric acid + iron→ iron sulphate + hydrogen

• Base/alkali + acid → salt + water

  • Sodium hydroxide + hydrochloric acid  Sodium chloride + water

• Acid + metal carbonate → salt + carbon dioxide + water

  • Nitric acid + magnesium oxide  magnesium nitrate + carbon dioxide + water

• Alkali + ammonium salt → salt + ammonia + water

  • Sodium hydroxide + ammonium chloride  sodium chloride + ammonia + water

• ==Acid: Proton Donors/ Dissociate into H+ ions==

  • Have pH between 1 (strong) and 6 (weak)
  • Turns blue litmus red
  • Turns methyl orange indicator red

• ==Bases: Proton Acceptors/ Dissociate into OH- ions==

  • Are the oxides and hydroxides of metals
  • Neutralise acids to give a salt and water only
  • Are mainly insoluble in water

• Alkalis: (are bases that dissolve in water)

  • Feel soapy to the skin
  • Turn litmus blue
  • Gives solutions with a ph greater than 7
  • · Give solutions that contain OH – ions

==Neutrality, acidity, alkalinity==

• pH scale runs from 1 – 14

Key facts:

• Acids have a ph less than 7

• The more acidic a solution, the lower the ph

  • Neutral substances, such as pure water have a ph of 7
  • Alkalis have ph greater than 7
  • Strong acid or base completely ionize in water
  • Weak acids partially ionize in water Ways to Measure pH:

• Substances that change colour when added to an acid/alkali are called indicators. They are often in solution form but can also be found as paper

  

==Metal and non-metal oxides==

• Acidic oxides: Non-metal oxides that dissolve in water and form an acidic solution
• Basic oxides: Metal oxides that dissolve in water and form basic solution
• Neutral oxides: Oxides with a pH of 7. Do not react with Acids or Alkalis
  • However there some exceptions for this rule, for example carbon monoxide.
• Amphoteric oxides: those that react with both an acid and an alkali to give a salt and water.

eg. zinc and aluminum oxides

Preparing Salts

==Preparing Soluble Salts==

Method A: Neutralization

• Excess insoluble compound (metal/base/carbonate) reacts with acid whilst being heated
• Insoluble base is filtered out
• Solution is heated in an evaporating dish to form soluble salt crystals

Method B: Titration

• Phenolphthalein is added to an alkali (soluble base)
• Add acid to solution using burette; note volume of acid required for solution to change color
• Repeat without indictor using noted acid volume
• Heat in evaporating dish to form soluble salt crystals

==Preparing Insoluble Salts==

Method C: Precipitation

• 2 soluble salts added to water and mixed

  Note: one soluble salt should always be a potassium or sodium solution (eg. potassium sulfate)

• Filter out and clean precipitate with distilled water

• Dry insoluble salt precipitate in oven

  

Tests

==Testing Cations==

==Testing for Anions:==

• Sulfate ions (SO42-):

  • Add dilute nitric acid, then add aq. barium nitrate
  • White precipitate formed

• Sulphite ions (SO32-):

  • Add acidified potassium permanganate and heat
  • Color changes from pink to colorless

• Halide ions:

  • Add nitric acid, then aqueous silver nitrate

• Nitrate ions (NO3-):

  • Add aqueous sodium hydroxide then add warm aluminum foil
  • Pungent gas produced, turns damp red litmus blue

• Carbonate ions (CO32-):

  • Add dilute hydrochloric acid
  • If bubbles/ gas produced turn limewater cloudy, carbonate ion present

==Flame Tests==

==Test for Gases:==