1. Identifying Ions
Noadswood Science, 2013

2. Identifying Ions To be able to identify ions (metals and non-metals)
Wednesday, April 26, 2017
Identifying Ions
To be able to identify ions (metals and non-metals)

3. Flame Tests
Flame tests are used to identify metal ions – they can identify which, if any, metals are present in a compound
Why do the different metals give out different colours during a flame test?
As the element is heated electrons are excited to higher energy levels. As these electrons return to their ‘ground state’ specific amounts of energy is released – this energy corresponds to particular wavelengths of light, so producing particular colours of light

4. Flame Tests
A nichrome wire loop is dipped into dilute hydrochloric acid and then rinsed in distilled water to clean it
The loop is then dipped into the sample and placed in the blue tip of a Bunsen burner on full flame – the colours are then observed…

5. Flame Tests Common metals and their colours: - Barium – pale green
Calcium – yellow-red
Copper – green-blue
Lead – blue flashes
Lithium – red
Sodium – orange
Potassium – lilac
Magnesium – white
Strontium – red

6. Flame Tests

7. Precipitation Test
In precipitation tests 2 dissolved substances react to form an insoluble solid (the precipitate)
Precipitation tests allow you to identify soluble ionic compounds…
Many ions like nitrates and lead which are poisonous can be extremely dangerous if they get into the water supply – forensic scientists can take samples of water and using precipitation tests can ensure dangerous levels do not occur…
Precipitates such as a barium meal are also used in medicine (to show the digestive system)!

8. Carbonate Tests Most carbonates are insoluble…
Carbonates give off carbon dioxide gas (CO2) when added to dilute acids
Method: -
Add your compound to dilute acid, e.g. dilute hydrochloric acid
Collect any gas given off
Bubble the gas through limewater – it the limewater turns milky the gas is carbon dioxide, meaning the compound contains carbonate ions (CO3-2)

9. White (colourless when excess NaOH added)
Metal Ion Test
Many metal hydroxides are insoluble causing them to precipitate out of a solution when formed
Some of these hydroxides have a characteristic colour
Method: -
Add a few drops of sodium hydroxide solution to the unknown solution
If a precipitate forms the colour can tell you which metal hydroxide was made
Calcium chloride + Sodium hydroxide  Calcium hydroxide + Sodium chloride
Metal Ion
Colour of Precipitate
Calcium (Ca+2)
White
Copper (Cu+2)
Blue
Iron (II) (Fe+2)
Green
Iron (III) (Fe+3)
Red / Brown
Lead (II) (Pb+2)
White (colourless when excess NaOH added)

10. Barium chloride + Copper sulfate  Barium sulfate + Copper chloride
Sulfate Test
Sulfates are tested for using hydrochloric acid and then barium chloride
Method: -
Add dilute hydrochloric acid to a solution of the unknown compound
Then add a few drops of barium chloride solution
If a white precipitate forms there are sulfate ions (SO4-2)
Barium chloride + Copper sulfate  Barium sulfate + Copper chloride

11. Silver nitrate + Copper chloride  Silver chloride + Copper nitrate
Halide Test
Halides are tested for using nitric acid and then silver nitrate
Method: -
Add dilute nitric acid to a solution of the unknown compound
Then add a few drops of silver nitrate solution
If a white precipitate forms = chloride ions (Cl-); a cream precipitate forms = bromide ions (Bl-); a yellow precipitate forms = iodide ions (I-)
Silver nitrate + Copper chloride  Silver chloride + Copper nitrate

12. Experiment
Your task is to carry out experiments to test if the three samples contain what they say they do…
Sample A – Copper carbonate
Sample B – Iron (III) Sulfate
Sample C – Iron (II) Chloride
You will need to follow the flow diagram and decide which substances you will mix for a positive identification…
Start with the cation (e.g. copper) and then the anion (e.g. carbonate)

13. Sample Identification