Reactions of acids

• Reactions of acids with metals

  1. Acid + metal -> salt + hydrogen

  2. These are redox reactions - one substance is reduced and another is oxidised

  3. Identify which substances are reduced and oxidised by looking at electrons gained and lost (following OIL RIG)
• Redox reaction


  A reaction where one substance is reduced and another is oxidised
• Neutralisation of acids and salt production

  1. Acid + alkali -> salt + water

  2. Acid + base -> salt + water

  3. Acid + metal carbonate -> salt + water + carbon dioxide
• The charges on the positive ion from the base/alkali/carbonate and the negative ion from the acid must add up to zero
• Making soluble salts


  1. Add the chosen solid insoluble substance to the acid, the solid will dissolve

  2. Keep adding until excess solid sinks to the bottom, indicating the acid has been neutralised

  3. Filter out excess solid, evaporate some water, then leave the rest to evaporate slowly (crystallisation)
• pH scale


  • Measures the acidity or alkalinity of a solution
  • pH 7 is neutral
  • pH < 7 is acidic
  • pH > 7 is alkaline
• Ionic equation for neutralisation

  H+(aq) + OH-(aq) -> H2O(l)
• Titration


  1. Wash burette with dilute HCl and water

  2. Fill burette to 100cm3 with acid

  3. Use 25cm3 pipette to add 25cm3 of alkali to conical flask

  4. Add indicator to conical flask

  5. Add acid from burette to alkali until end-point is reached (as shown by indicator)

  6. The titre is the difference between the first and second burette readings

  7. Repeat to gain more precise results
• Titration calculations

  • 1dm3 = 1000cm3
  • One mole of a substance in grams is the same as its relative atomic mass in grams
• Calculating concentration from titration


  Convert volumes to dm3

  2. Work out moles of NaOH

  3. Use mole ratio from equation to work out moles of HCl

  4. Calculate concentration = moles / volume
• Strong acid


  Completely ionised in aqueous solution (e.g. HCl, HNO3, H2SO4)
• Weak acid


  Partially ionised in aqueous solution (e.g. ethanoic, citric, carbonic acids)
• Strength of acid


  The stronger the acid, the lower the pH (for a given concentration of aqueous solutions)
• pH decreases by 1 unit


  H+ concentration of the solution increases by a factor of 10
• Strong/weak and concentrated/dilute are not the same - strong/weak refers to H+ ion concentration, concentrated/dilute refers to amount of substance in a given volume