AQA A-level chemistry chemical tests Questions and Answers

AQA A-level chemistry chemical tests Questions and Answers test for Carbon Dioxide (CO2 ) turns limewater milky (sparingly soluble Ca(OH) 2 forms insoluble CaCO3 ) Chlorine (Cl2 ) test bleaches damp litmus paper (Cl2 reacts with water to form HCl and HOCl) Hydrogen (H2 ) test pops with a lighted splint Oxygen (O2 ) test relights a glowing splint Carbonate (CO 3 2- ) test add dilute acid; effervescence, carbon dioxide produced Sulfate (SO4 2- ) test add dilute nitric acid then aqueous barium nitrate. Gives white precipitate Chloride (Cl - ) test add dilute nitric acid then aqueous silver nitrate. Gives white precipitate. Dissolves in dilute ammonia to give colourless solution (of [Ag(NH 3 ) 2 ] + ) Bromide (Br - ) test add dilute nitric acid then aqueous silver nitrate. Gives cream precipitate. Dissolves in concentrated ammonia but not in dilute ammonia Iodide (I - ) test add dilute nitric acid then aqueous silver nitrate. Gives yellow precipitate. Does not dissolve in either concentrated or dilute ammonia Iron II (Fe 2+ ) test add aqueous sodium hydroxide gives green precipitate, insoluble in excess Iron III (Fe 3+ ) test add aqueous sodium hydroxide gives orange/brown precipitate, insoluble in excess Copper (Cu 2+ ) test add aqueous sodium hydroxide gives blue precipitate, insoluble in excess. Or add ammonia: gives a blue precipitate which dissolves in excess to give a blue solution Calcium (Ca 2+ ) test add aqueous sodium hydroxide gives white precipitate, insoluble in excess. Aluminium (Al 3+ ) test add aqueous sodium hydroxide gives white precipitate which dissolves in excess H + (any acid) test turns blue litmus red or makes sodium carbonate effervesce (makes CO 2 gas) H2O test turns white anhydrous copper (II) sulphate into blue hydrated copper (II) sulphate. It also turns blue anhydrous cobalt (II) chloride into pink hydrated cobalt (II) chloride reaction is reversible, colour changes reversed when hydrated salts are heated. Test for Unsaturated hydrocarbons turns bromine water from orange to colourless. Test for aldehydes produces a silver mirror from a colourless solution of Tollens' reagent (or produces a red precipitate from blue coloured Fehling's solution (needs heat)) Tests for organic (and other) acids (carboxylic acid) they release CO2 (bubbles of gas are observed) when shaken with sodium carbonate solution Test for acid chloride gives misty fumes with water Test for alcohol add acidified potassium dichromate (K2Cr2O7) orange to green (Cr3+) Manganate ion change of colour when reduced, goes from deep purple to colourless solubility of nitrates? All nitrates are soluble. solubility of group 1 and ammonium ions? All compounds of group 1 and ammonium ions are soluble. solubility of chlorides? All chlorides except for those of Ag, Pb and Hg are soluble. solubility of hydroxides? All hydroxides are insoluble (except those of group 1, ammonium, barium and strontium). (Calcium hydroxide is 'sparingly' soluble and a solution is known as limewater). Aluminium (also zinc and chromium) hydroxide is amphoteric and dissolves in excess hydroxide solubility of metal carbonates? All metal carbonates (except those of group 1, and ammonium) are insoluble insoluble black solid? might be carbon (graphite), iodine or MnO 2 . insoluble yellow solid? An insoluble yellow solid might be sulphur test for sulfate ion add nitric acid (removes carbonate ions so no other ppt forms), add barium chloride, barium sulfate forms, white ppt. test for amines turns litmus paper blue (naturally basic) test for arene burn in air. produces smokey flame and soot.