C3 - Chemical Tests Flashcards
Describe how flame tests are done
Clean a wire loop by dipping it into hydrochloric acid and rinsing it with distilled water
Dip the wire loop into a sample of the compound and put it in the clear blue part of the Bunsen flame
What are the 2 chemical tests for positive ions and which one would you try first?
Flame tests (try this first)
Precipitation with NaOH
List the 5 ions that can be flame tested and give the colour of the flame for each
Lithium (Li+) - Crimson
Sodium (Na+) - Yellow
Potassium (K+) - Lilac
Calcium (Ca2+) - Red
Barium (Ba2+) - Green
Describe how precipitation with NaOH testing is done
Many metal hydroxides are insoluble and precipitate out of solution and have a characteristic colour
Add a few drops of sodium hydroxide solution to the solution of the mystery compound
If you get a coloured insoluble hydroxide, you can tell what the positive ion is
List the 6 ions that can be identified by precipitation with NaOH and give the colour of their precipitation
Calcium (Ca2+) - White
Copper (Cu2+) - Blue
Iron (Fe2+) - Green
Iron (Fe3+) - Brown
Aluminium (Al3+) - White at first but redissolves to turn colourless
Magnesium (Mg2+) - White
What are the 2 chemical tests for negative ions?
Carbonate testing
Testing for halides and sulphates
Describe how carbonate testing is done
You can test to see if a gas is carbon dioxide by bubbling it through line water. It is carbon dioxide if the limewater turns cloudy
You can use this to test for carbonates because carbonates react with dilute acids to form carbon dioxide
Describe how testing for halides works
You add dilute nut ric acid and then silver nitrate solution and a colour Ed precipitate will form
List the 3 halides that can be tested and give the colour of their precipitate
Chloride (Cl-) - White
Bromide (Br-) - Cream
Iodide (I-) - Yellow
Describe how testing for sulphates works
Add dilute hydrochloric acid and then barium chloride solution
A white precipitate of barium sulphate means the original compound was a sulphate
