Chem Practical Notes

NOTESFORUSEIN QUALITATIVE ANALYSIS TESTS FOR ANIONS anion test test result carbonate (CO;) |add dilute acid effervescence, carbon dioxide produced chloride (CI) [in solution] acidify with dilute nitric acid, then add whiteppt. aqueous silver nitrate add aqueous sodium hydroxide, then | ammonia produced aluminium foil; warm carefully nitrate (NO;) in solution] sulphate(SO;) in solution] acidify with dilute nitric acid, then add white ppt. aqueous barium nitrate TESTS FOR AQUEOUS CATIONS effect of aqueous sodium hydroxide cation effect of aqueous ammonia ammonium (NH,) ammonia produced on warming calcium (Ca*) white ppt., insoluble in excess no ppt. copper(II) (Cu*") light blue ppt., insoluble in excess light blue ppt., soluble in excess giving a dark blue solution iron(11) (Fe*") green ppt., insoluble in excess green ppt., insoluble in excess red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess iron(11) (Fec) lead(II) (Pb*") white ppt., soluble in excess giving | white ppt., insolublein excess a colourlesssolution zinc (Zn) white ppt., soluble in excess giving | white ppt., soluble in excess giving a a colourless solution colourless solution [Lead(lI) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.] TESTS FOR GASES test and result gas ammonia (NH,) turns damp red litmus paper blue given white ppt. with limewater (ppt. dissolves with excess CO;) carbon dioxide (CO:) chlorine (C,) bleaches damp litmus paper hydrogen (H) "pops with a lighted splint relights a glowing splint sulphur dioxide (SO,) turns aqueous potassium dichromate (VI) from orange to green oxygen (O:)

COLOURS OF SOME COMMON METAL HYDROXIDES Calcium hydroxide white Copper(11) hydroxide light blue Iron(11) hydroxide green Iron(111) hydroxide red-brown Lead(11) hydroxide white Zinc hydroxide white 2

NOTES ON QUALITATIVE ANALYSIS In the practical examination, candidates are usually provided with unknown substance(s) and the necessary experimental procedures. They are expected to carry out testsaccording to the given procedures, record all observations and deduce the nature of the unknown substance(s). The following are some notes that could be of great help to candidates when performing a qualitative experiment. 1. If candidates are given the following instruction: (a) Carry out the following experiments and record all your observations and deductions of the unknown substance W." Such instruction implies that candidates are expected to identify the unknown with the results of the experiments. For example: W is copper(11) nitrate. (b) You are not required to identify the unknown substance W but you must describe all that you observe, identify any gas evolved and state any conclusions you draw from the experiments." In this case, candidates are expected to state the action of the unknown substance W with other reagents or certain identifiable products produced by W. For example: W is an acid or alkali in nature or W is re