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: