Specifications
Core Practicals
Core Practical 7
Identifying ions (chemistry only)
Introducing the Practical
Tests must be carried out to determine the ions present.
This will include gas tests, flame tests and precipitation reactions.
Risk Assessment
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.
Apparatus
Each group will need:
-
Bunsen burner
-
heat‐resistant mat
-
test tubes
-
test tube rack
-
test tube holder
-
flame test loops
-
spatula
-
dropping pipettes
-
barium chloride solution
-
hydrochloric acid
-
silver nitrate solution
-
nitric acid
-
sodium hydroxide solution
-
distilled water
-
samples of salts to test (labelled A-D)
Method
-
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
click here if you need to check back on your tests for salts
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.
[6 marks}
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)
Flame Tests
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)