Analysing substances

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  • Created by: Punkzebra
  • Created on: 06-05-14 19:36

Flame Test for Metal Ions

This is how you would carry out a typical flame test:

  1. dip a clean flame test loop in the sample solution

  2. hold the flame test loop at the edge of a Bunsen burner flame

  3. observe the changed colour of the flame, and decide which metal it indicates

Results

  • Lithium compounds -crimson flame
  • Sodium compounds - yellow flame
  • Potassium compounds - lilac flame
  • Calcium compounds - red flame
  • Barium compounds - green flame
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Using precipitation to identify metal ions

Precipitate - An insoluble solid formed in a reaction

For the exam you need to know that-

  • Aluminium, calcium, magnesium,
  • copper(II), iron(II) and iron(III)

-Ions all form precipitates when reacted with sodium hydroxide solution.

Results-Colour of Precipitate.

  • Aluminium - White.
  • Calcium - White.
  • Magnesium - White.
    • When excees sodium hydocide solution is added to aluminium - precipitate dissolves. 
    • To distingish between calcium and magnesium use flame test.
  • Copper(II) - Blue.
  • Iron(II) - Green.
  • Iron(III) - Brown.


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Using precipitation to identify non-metal ions

Testing for carbonate ions

  • They react with dilute acids to produce CO2 and H2O
  • CO2 produces a white participate with limewater
    • Which turns limewater cloudy

Testing for halide ions

  • A few drops of dilute nitric acid are added to the unknown solution
  • A few drops of silver nitrate solution are then added
  • It forms a coloured precipitate 
  • Which are: 
    • Chloride - White 
    • Bromide - Cream
    • Iodide - Yellow

Testing for sulfate ions

  • A few drops of dilute hydrochloric acid are added to the solution
  • A few drops of barium chloride solution are then added
  • Forms a white precipitate of barium sulfate
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Titration

  • A pipette accurately measures a volume of an alkali
  • A pipette filler to put solution in pipette. 
  • Alkali put in conical flask.
  • A few drops of a suitable indicator added to conical flask. 
    • To show when acid and alkali have neutralised - titration complete.
  • Acid placed in burette and starting volume noted.
  • the tap on burrette is opends slighlty to allow a slow droping of acid into alkali, 
    • when close to nuetralisation-one drop at a time
  • Flask is swirled to mix 
  • colour change shows correct amount of acids been added to react completely with alkali 
  • volume of acid added from the burette is noted. 
  • The titration results can then be used to calculate the concentration of the acid or alkali 
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Titration diagram

(http://ts2.mm.bing.net/th?&id=HN.608041531012547448&w=300&h=300&c=0&pid=1.9&rs=0&p=0)

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