O Level Chemistry (Notes For Qualitative Analysis)
Do note that the notes for qualitative analysis is a document given for the O level syllabus only for certain papers depending on which paper or what is tested. For Papers where questions in Qualitative Analysis are possibly tested, it is not given.
However the note is a good summary of tests on anion, cation and gas and the subsequent precipitate.
Chemistry (Syllabus 6092) – O Level Syllabus 2024
Qualitative Analysis
Test for Anions
| Anion | Test | Test result |
| carbonate (CO3 2–) | add dilute acid | Effervescence, carbon dioxide produced |
| chloride (Cl –) [in solution] | acidify with dilute nitric acid, then add aqueous silver nitrate | white ppt. |
| iodide (I–) [in solution] | acidify with dilute nitric acid, then add aqueous silver nitrate | yellow ppt |
| nitrate (NO3 –) [in solution] | add aqueous sodium hydroxide, then aluminium foil; warm carefully | ammonia produced |
| sulfate (SO4 2–) [in solution] | acidify with dilute nitric acid, then add aqueous barium nitrate | white ppt. |
Test for Aqueous Cations
| Cation | Effect of aqueous sodium hydroxide | Effect of aqueous ammonia |
| aluminium (Al 3+) | white ppt., soluble in excess giving a colourless solution | White ppt., insoluble in excess |
| ammonium (NH4 +) | ammonia produced on warming | – |
| calcium (Ca2+) | white ppt., insoluble in excess | no ppt. |
| copper(II) (Cu2+) | light blue ppt., insoluble in excess | light blue ppt., soluble in excess giving a dark blue solution |
| iron(II) (Fe2+) | green ppt., insoluble in excess | green ppt., insoluble in excess |
| iron(III) (Fe3+) | red-brown ppt., insoluble in excess | red-brown ppt., insoluble in excess |
| zinc (Zn2+) | white ppt., soluble in excess giving a colourless solution | white ppt., soluble in excess giving a colourless solution |
Test for Gases
| Gas | Test and Test Results |
| Ammonia (NH3) | turns damp red litmus paper blue |
| Carbon dioxide (CO2) | gives white ppt. with limewater (ppt. dissolves with excess CO2) |
| 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 |
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