Introducing the Practical
Tests must be carried out to determine the ions present.
This will include gas tests, flame tests and precipitation reactions.
As a general rule, eye protection (goggles) must be worn for all practicals.
This risk assessment is provided as an example only, and you must perform your own risk assessment before doing this experiment.
Each group will need:
test tube rack
test tube holder
flame test loops
barium chloride solution
silver nitrate solution
sodium hydroxide solution
samples of salts to test (labelled A-D)
carry out one (or more) test(s) on each salt - you may need to dissolve a sample of salt in a little distilled water if you are given solids
record your observations carefully and repeat any tests that do not get clear results
Exam Question and Model Answer
Describe a series of experiments to distinguish between the following compounds: sodium chloride, sodium carbonate, potassium chloride, potassium iodide, potassium sulfate.
Level 1 (1-2 marks)
First, do a flame test on all the chemicals. Depending on which elements are present will mean they turn different colours.
Then test them by adding dilute nitric acid (then silver nitrate).
Then test by adding barium chloride - will make a precipitate if sulfate is present.
Level 2 (3-4 marks)
sodium compounds will give a yellow colour
potassium compounds give a lilac colour
Dilute nitric acid, then silver nitrate
carbonates will fizz (the gas produced turns limewater cloudy)
chlorides will produce a white precipitate
iodides will produce a yellow precipitate
sulfates does not produce a precipitate (adding barium chloride produces a white precipitate)
Level 3 (5-6 marks)
First, do a flame test on all the chemicals. Depending on which elements are present will mean they turn different colours:
sodium chloride, and sodium carbonate will give a yellow colour
potassium chloride, potassium iodide, potassium sulfate will give a lilac colour
Then test them by adding dilute nitric acid (then silver nitrate). Carbonates will fizz, chlorides turn white, iodides turn yellow.
sodium carbonate will fizz (the gas produced turns limewater cloudy)
sodium chloride, potassium chloride will produce a white precipitate
potassium iodide will produce a yellow precipitate
potassium sulfate does not produce a precipitate (adding barium chloride produces a white precipitate)