Aims of Experiment
Use of chemical tests to identify the ions in unknown single ionic compounds
In this experiment you will:
- use flame tests and add a range of solutions to analyse a range of known ionic compounds
- use your results to identify the ions present in an unknown solution
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)
As a general rule, eye protection (goggles) must be worn for all practicals.
|barium chloride solid
||harmful if inhaled, toxic if swallowed
||use dilute solutions, get your teacher to use it
|silver nitrate solution
||serious eye irritation, skin irritation
||avoid skin contact by using dropper bottles/wearing gloves
This risk assessment is provided as an example only, and you must perform your own risk assessment before doing this experiment.
- 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
Results and Analysis
|salt solution||test||observation||ion present|
|A||flame test||yellow flame|
|A||hydrochloric acid and barium chloride solution added
|B||sodium hydroxide added
|B|| nitric acid and silver nitrate solution added
Use the results to identify the ions present in each salt, and then to name the salts.
A is sodium sulfate.
B is copper(II) chloride.
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)