Flame Test for Metal Ions
This is how you would carry out a typical flame test:
dip a clean flame test loop in the sample solution
hold the flame test loop at the edge of a Bunsen burner flame
observe the changed colour of the flame, and decide which metal it indicates
- Lithium compounds -crimson flame
- Sodium compounds - yellow flame
- Potassium compounds - lilac flame
- Calcium compounds - red flame
- Barium compounds - green flame
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.
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
- 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