Practical P2 - Tests For Ions

Question 1

how can you test for carbonates
3 points

Answer 1

1) use a pipette to add a few drops of dilute acid to a test tube
2) connect this test tube to a test tube containing limewater
3) if carbonate ions are present, their reaction with the acid produces CO2, turning limewater cloudy

Question 2

how can you test for sulfates
2 points

Answer 2

1) use a dropping pipette to add a couple of drops of dilute HCL and then a few drops of barium chloride solution to a test tube with the thing you’re testing
2) if sulfates are present a white precipitate of barirum sulfate will form

Question 3

how can you test for halides
4 points

Answer 3

1) add a couple drops of dilute nitric acid and then a few drops of silver nitrate
2) chloride: gives white precipitate of silver chloride
3) bromide: gives cream precipitate of silver bromide
4) iodide: gives yellow precipitate of silver iodide

Question 4

how can you use flame tests to test for metal ions
4 points

Answer 4

1) heat your substance and see what colour the flame changes
2) first clean a nichrome or platinum wire, then hold it in a blue flame, the flame might change colour for a bit, but once it’s blue again it’s clean
3) then dip it into the sample of what you’re testing and see the colour
4) this only works for a single metal ion, if the substance is a mixture, some of the colours could be hidden

Question 5

whats the result for the flame test
5 points

Answer 5

1) lithium ions: crimson flame
2) sodium ions: yellow flame
3) potassium ions: lilac flame
4) calcium ions: orange-red flame
5) copper ions: green flame

Question 6

how can you test for some ions using NaOH
2 points

Answer 6

1) many metal hydroxides are insoluble and a precipitate will form, some being coloured
2) add a few drops of sodium hydroxide solution to your mystery compound and see if it forms a coloured precipitate

Question 7

what are the results for using NaOH to test for metal ions
6 points

Answer 7

1) calcium ions: white precipitate
2) copper (II) ions: blue precipitate
3) iron (II) ions: green precipitate
4) iron (III) ions: brown precipitate
5) aluminium ions: white at first then redissolves in excess NaOH to form colourless solution
6) magnesium ions: white precipitate