2.14

• Acids

  Any substance that increases the concentration of the H+ ion when it dissolves in water
• Bases

  A substance that can accept hydrogen ions in water and can neutralise an acid
• Acid-base reaction in water

  1. Acid (HA) + water ⇌ H3O+ + A-

  2. Base (B) + water ⇌ BH+ + OH-
• Hydronium ion (H3O+)


  Makes solutions acidic
• Hydroxide ion (OH-)


  Makes solutions basic
• Polyprotic acids


  Acids that can donate more than one proton (e.g. sulfuric acid, phosphoric acid)
• Ammonia (NH3)


  Reacts with water to form ammonium ions (NH4+) and hydroxide ions (OH-)
• Ammonia reaction

  • NH3 + H2O ⇌ NH4+ + OH-
• Metal + Acid

  Metal + Acid → Salt + Hydrogen
• Metal oxide/hydroxide + Acid

  Metal oxide/hydroxide + Acid → Salt + Water
• Metal carbonate + Acid

  Metal carbonate + Acid → Salt + Carbon dioxide + Water
• Mole

  Amount of substance, calculated from concentration and volume
• Titration

  Acid or alkali of unknown concentration is added drop-wise to an acid or alkali of known concentration until neutralisation (indicated by colour change)
• Titrations can be used to determine the concentration of an acid or alkali
• Acid-base titration

  1. Put acid or alkali in burette

  2. Put unknown concentration in conical flask

  3. Add indicator

  4. Titrate until indicator changes color (endpoint)

  5. Measure volume of acid/alkali added
• Reading the burette

  Read at the bottom of the meniscus at eye level
• Concordant results

  Titration results within 0.1 cm3 of each other
• Indicators


  • Phenolphthalein (colorless in acid, pink in alkali)
  • Methyl orange (yellow in acid, red in alkali)
• Making a standard solution


  1. Weigh solid accurately

  2. Transfer solid to beaker, rinse

  3. Dissolve solid fully

  4. Transfer to volumetric flask using funnel

  5. Fill to graduation line

  6. Mix thoroughly
• Standard solutions have known concentrations
• Calculating mass of solid for standard solution


  1. Calculate moles of solution needed

  2. Use moles and molar mass to calculate mass of solid
• Titration calculations

  1. Write balanced equation

  2. Calculate moles of acid/alkali from volume and concentration

  3. Use mole ratio to find moles of other reactant

  4. Calculate concentration from moles and volume
• Calculating volume of alkali from titration


  1. Calculate moles of acid from volume and concentration

  2. Use mole ratio to find moles of alkali

  3. Calculate volume of alkali from moles and concentration
• To convert decimal cubes to cm3, multiply by 1000