C4

• pH scale

  Measure of how acidic or alkaline a solution is, ranging from 0 to 14
• Acidic solution

  pH less than 7
• Alkaline solution

  pH greater than 7
• Neutral solution

  pH of exactly 7
• pH testing


  • Using an indicator dye that changes colour depending on pH
  • Using a pH meter and probe to measure pH electronically
• Acids

  Form hydrogen ions (H+) when dissolved in water
• Alkalis

  Form hydroxide ions (OH-) when dissolved in water
• Neutralisation reaction

  Acid reacts with alkali to form salt and water
• Hydrogen ions (H+) and hydroxide ions (OH-)

  React to produce water
• Titration

  Experiment to find the volume of a reactant needed to completely react with another reactant
• Carrying out a titration

  1. Measure alkali volume

  2. Add indicator

  3. Fill burette with acid

  4. Take initial acid volume reading

  5. Do rough titration

  6. Spot end-point colour change

  7. Take final acid volume reading

  8. Repeat accurate titration 3 times

  9. Calculate mean volume of acid used
• Indicators for titrations

  • Universal indicator gives gradual colour change
  • Phenolphthalein, methyl orange, litmus give distinct colour change at end-point
• Titrations require risk assessment for acid and alkali hazards
• Strong acids


  Ionise completely in water to release H+ ions
• Weak acids


  Partially ionise in water to release H+ ions
• A change in H+ concentration by a factor of 10 changes the pH by 1
• Strong acid solution

  Has lower pH than weak acid solution of same concentration
• Concentrated acid

  High amount of acid per unit volume
• Strong acid


  Ionises completely to release H+ ions
• Hydrochloric acid gas isn't acidic
• H ion

  A proton
• Strong acids

  Acids that ionise completely in water, releasing all H ions
• Weak acids

  Acids that only partially ionise in water, not releasing all H ions
• Dissociation of acids

  Acids added to aqueous solution ionise to produce H ions and other ions
• Acid strength

  Determines proportion of acid particles that dissociate to produce H ions in solution
• Reactions of acids

  Involve H ions reacting with other substances
• Concentration of H ions

  Determines rate of acid reactions, strong acids have higher concentration
• pH

  Measure of concentration of H ions in a solution, lower pH means higher H ion concentration and more acidic
• pH decreases by 1


  H ion concentration increases by a factor of 10
• Acid strength (strong or weak) tells proportion of acid molecules that ionise, concentration measures total dissolved acid molecules
• Metal oxides and metal hydroxides


  Bases that can react with acids in neutralisation reactions
• Reaction of metal oxides/hydroxides with acids


  Produces a salt and water
• Salt


  Product of neutralisation reaction, name depends on metal ion and acid
• Reactions of metal carbonates with acids

  • Produce a salt, carbon dioxide, and water
• To make a soluble salt, react an acid with a metal or insoluble base (oxide, hydroxide, carbonate)
• Making soluble salts from acids and insoluble bases

  1. Put acid in beaker and gently warm

  2. Add insoluble base and stir until reaction complete

  3. Filter out excess insoluble base

  4. Evaporate solution to get pure salt crystals
• The reactivity series orders metals by how easily they form positive ions
• Metals in reactivity series


  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Carbon
  • Hydrogen
  • Zinc
  • Iron
  • Copper
• More reactive metals can displace less reactive metals from compounds
• Reactive metals react with water to form metal hydroxides and hydrogen gas