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Qualitative Analysis Table – O Level Chemistry

qualitative analysis table for O Level chemistry where we look at the qualitative analysis tests for cations, anions and gases.

In O Level Chemistry, students learn the qualitative analysis table of cations, anions and also testing for gases. Let’s look at these three groups of chemical tests and more in this post.

Do note that for the practical exam (paper 3 for Pure Chemistry), the tables for testing of cations, anions and gases are provided (so no need to memorize them). However, students still need to know them for their theory paper (paper 1 and 2 for pure Chemistry).

Qualitative analysis table of cations

Here are the list of qualitative analysis of cations that are tested in O Level Chemistry.

Do note that since all tests involve precipitation, the test is for aqueous ions (i.e. the compound must be dissolved in water during the tests).

The following is not the exact table you will see in your data booklet. I have added in my notes as well, so that it is more useful for students. The portion that I’ve added are in italics.

cationeffect of aqueous sodium hydroxide (NaOH)effect of aqueous ammonia (NH3)
aluminium (Al3+)white ppt., soluble in excess giving a
colourless solution

white ppt is Al(OH)3.
white ppt., insoluble in excess

white ppt is Al(OH)3.
ammonium (NH4+)ammonia produced on warming
calcium (Ca2+)white ppt., insoluble in excess

white ppt is Ca(OH)2.
no ppt.
copper(II) (Cu2+)light blue ppt., insoluble in excess

blue ppt is Cu(OH)2.
light blue ppt., soluble in excess giving a
dark blue solution

blue ppt is Cu(OH)2.
iron(II) (Fe2+)green ppt., insoluble in excess

green ppt is Fe(OH)2.
green ppt., insoluble in excess

green ppt is Fe(OH)2.
iron(III) (Fe3+)red-brown ppt., insoluble in excess

red-brown ppt is Fe(OH)3.
red-brown ppt., insoluble in excess

red-brown ppt is Fe(OH)3.
lead(II) (Pb2+)white ppt., soluble in excess giving a
colourless solution

white ppt is Pb(OH)2.
white ppt., insoluble in excess


white ppt is Pb(OH)2.
zinc (Zn2+)white ppt., soluble in excess giving a
colourless solution

white ppt is Zn(OH)2.
white ppt., soluble in excess giving a
colourless solution

white ppt is Zn(OH)2.
qualitative analysis table to test for aqueous cations

Some items to note for testing of cations:

  • To distinguish between lead(II) ions and aluminium ions, add a solution containing chloride. Lead(II) ions will form a white precipitate of lead(II) chloride upon adding of the chloride solution. For the solution containing aluminium ions, no white precipitate will be observed.
  • All the precipitates formed in the cation qualitative analysis table above are hydroxides (even when we add aqueous ammonia). The hydroxide ions that form the precipitate from the solution, is formed from the dissociation of ammonia in water (not in O Level Chemistry syllabus).

NH3 + H2O ⇌ NH4+ + OH

How to remember the cation table easily?

I would group similar ones together.

  • First, start off my remembering that we use aqueous sodium hydroxide and aqueous ammonia to test for the cations.
  • Next, remember that there are 3 cations that formed coloured (i.e. non- white) precipitate.

copper (II) –> blue

iron (II) –> blue

iron (III) –> red-brown

  • The rest form white precipitate, and give colourless solution (if the precipitate are soluble)
  • Al3+, Pb2+ and Zn2+ forms precipitate soluble in excess aqueous sodium hydroxide
  • Cu2+ and Zn2+ forms precipitate soluble in excess aqueous ammonia
  • ammonia is different (it needs heating with NaOH, and we test for gas instead of observe precipitate)
  • Ca2+ does not give a precipitate with aqueous ammonia

Qualitative Table for Anions

aniontesttest result
carbonate (CO32-)add dilute acideffervescence, carbon dioxide produced
chloride (Cl)acidify with dilute nitric acid, then add
aqueous silver nitrate
white ppt
iodide (I)acidify with dilute nitric acid, then add
aqueous silver nitrate
yellow ppt.
nitrate (NO3)add aqueous sodium hydroxide, then
aluminium foil; warm carefully
ammonia produced
sulfate (SO42-)acidify with dilute nitric acid, then add
aqueous barium nitrate
white ppt.
qualitative analysis table for anions

Some items to note:

  • The tests for chlorides, iodide and sulfate involve precipitation. Hence, both reagents should start off as aqueous solutions. Do also note that precipitation reaction will precipitate out ionic compounds that are insoluble in water (see solubility of ionic compounds for details).
  • For the test for chlorides and iodides, aqueous lead(II) nitrate could be used instead of aqueous silver nitrate. chloride ions will give a white ppt with lead(II) nitrate, while iodide ions will give a yellow ppt with lead(II) nitrate.
  • Take a look at the test for nitrates vs the test for ammonium ions (see cation table). You will notice that the difference lies in whether aluminium foil is used or not. Since test for ammonium ions does not require aluminium foil, this means that whether you use aluminium foil or not, if there is ammonium ions, ammonia gas will be produced. However, for nitrate, we need to use aluminium foil in order for ammonia to be generated upon heating.

Testing for gases

GasTest and test result
ammonia (NH3)turns damp red litmus paper blue
carbon dioxide (CO2)gives white ppt. with limewater
chlorine (Cl2)bleaches damp litmus paper
hydrogen (H2)‘pops’ with a lighted splint
oxygen (O2)relights a glowing splint
sulfur dioxide (SO2)turns aqueous acidified potassium manganate(VII) from purple to colourless

Learn O Level Chemistry topics on-demand

Want this topic and other topics tested in the O Level Chemistry (Pure) syllabus? Check out our On-demand chemistry courses written based on the Singapore O Level Chemistry syllabus.

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