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Acids, Bases & Salts (Definitions (Acids are substances which…

- - - - Acid – Red
      - Alkali – Blue
    - - Acid – Colourless
      - Alkali, neutral – Pink
    - - Acid – Red
      - Alkali – Yellow
- - - - Man-made: eg. HCl, H2SO4, HNO3
      - Natural: eg. ethanoic acid, citric acid, carbonic acid
    - - Man-made: eg. NaOH, Na2CO3
      - Natural: eg. ammonia
- - - - Magnesium
        
        Reacts rapidly with dilute acids
        
        Makes a colourless solutions of magnesium salts
      - Zinc
        
        Reacts readily but not as rapidly as magnesium
        
        Colourless salts
      - Aluminium
        
        Reacts in theory with dilute acids
        
        Colourless aluminium salts
        
        In practice, the impervious coating of aluminium oxide on the surface prevents the reaction unless this layer is removed
  - - - Unreactive metals, eg. copper, do not react
        
        Only a suitable reaction using a moderately reactive metal eg. zinc, magnesium
        
        Very reactive metals, eg. sodium, react explosively
      - eg. Zn + HCl –––> ZnCl2 + H2
    - - eg. CuO + H2SO4 –––> CuSO4 + H2O
    - - Ammonia is also able to act as a base and so can react with an acid to produce an ammonium salt
        
        eg. ammonia + HCl –––> ammonium chloride
- - - - Mix together two solutions that each contain one of the two ions required to form the salt. A precipitate is formed
      - Filter off the precipitate
      - Wash by pouring a little distilled water over the precipitate in the filter paper
      - Leave to dry
      - *The precipitate is washed to remove any spectator ions – ions that did not form the insoluble salt and remained unchanged in the solution
  - - - A known volume (usually 25cm3) of acid is measured into a conical flask using a pipette
      - A few drops of indicator, such as phenolphthalein, is added
      - The alkali is placed in a burette and slowly added to the conical flask containing the acid
      - When the indicator changes colour the volume of alkali added is recorded
      - The process is repeated without the indicator using the required volume of alkali to give a pure solution
      - The salt solution is warmed in an evaporating basin and concentrated by removed about 2/3 of the solution
      - The solution is left to crystallise, forming large crystals
      - *The acid and alkali can be swapped around, it doesn't matter
      - *It can be done without an indicator:
        
        Using a pH meter
        
        Neutralisation is exothermic – the maximum temp reached corresponds to the neutral solution
        
        H+ and OH- ions increase conductivity. Minimum conductivity corresponds to the neutral solution as there will be the fewest of these ions present
  - - - The appropriate acid is warmed over a Bunsen burner in a beaker
      - A small portion of the appropriate, insoluble, metal oxide or carbonate is stirred into the acid
      - Keep adding the oxide or carbonate until it doesn't react (and dissolve)
      - Filter the solution to remove the unreacted base. The filtrate is the pure salt solution
      - Concentrate the solution by evaporating 2/3 in an evaporating basin
      - Leave to crystallise