Chemical Analysis

c3 aqa chemical analysis: flame tests, tests for positive/negative ions.

  • Created by: Punam
  • Created on: 10-05-12 09:19

Flame Tests

Flame tests: Put compound in a platinum wire loop dipped in hydrochloric acid, and put it over a blue bunsen flame.

Calcium gives a BRICK RED flame

Lithium gives a BRIGHT RED flame

Sodium gives a GOLDEN flame

Barium gives a GREEN flame

Potassium gives a LILAC flame

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Tests for Positive Ions

Put unknown substance in Sodium Hydroxide (NaOH) solution.

Aluminium, Calcium, and Magnesium ions form White Percipitate. To find out which one specifically, add more NaOH--aluminium ions dissolve in it eventually. If it doesn't dissolve its either calcium or magnesium. To find out if its calcium or magnesium, we can do flame tests (Ca--brick red flame, Mg--no particular colour)

Copper (II) ions form light blue percipitate

Iron (II) forms a dirty green percipitate

Iron (III) forms a reddish-brown percipitate

Ammonium ions react with NaOH to form ammonia and water. When ammonia and water is forms, we can heat up solution and test the gas given off with damp red litmus paper (which would turn blue).

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Tests for Negative Ions

Carbonates: add HCL to substance, if it fizzes it gives out CO2 gas. Pump gas into limewater--if it turns milky, then its CO2.

Halides: add dilute nitric acid and silver nitrate solution to the substance...

  • Chloride ions form a WHITE PERCIPITATE
  • Bromide ions form a CREAM PERCIPITATE
  • Iodine ions form a PALE YELLOPW PERCIPITATE

Sulphates: add HCL and barium chloride solution. If sulphate ions are present then a white percipitate is formed.

Nitrate: Test for ammonia is used again here. Add NaOH to unknown substance and warm it. If no ammonia is detected, add aluminium powder, so nitrate ions turn into ammonia so can be detected.

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Thankyou, these were really helpful :) Can you do ones for the testing of nitrates, sulfates etc.? :)



Ashleigh wrote:

Thankyou, these were really helpful :) Can you do ones for the testing of nitrates, sulfates etc.? :)

On the third card i did put tests for Sulphates (in green) and nitrates (in red) :D

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