Inorganic Qualitative Tests for Gases And Non-Metallic Elements

INORGANIC Qualitative TESTS for gases and non–metallic elements
CHEMICAL TEST FOR ...	TEST METHOD	OBSERVATIONS	TEST CHEMISTRY and comments
hydrogen gas H2	Apply a lit splint or spill.	A squeaky pop! (might see condensation on test tube)	2H2(g) + O2(g) ==> 2H2O(l) + energy!
Chemical test for carbon dioxide gas CO2	Bubble the gas into limewater (aqueous calcium hydroxide solution).	It turns cloudy – fine milky white precipitateof calcium carbonate. BEWARE – the calcium carbonate precipitate dissolves in excess carbon dioxide, so don't overdo the test!	Ca(OH)2(aq) + CO2(g) ==> CaCO3(s) + H2O(l)If excess carbon dioxide bubbled through you form a clear colourless solution of calcium hydrogencarbonate. CaCO3(s) + H2O(l) + CO2(aq) ==> Ca(HCO3)2(aq) so beware of overdoing this test!
Chemical test for oxygen gas O2	Apply a glowing splintor spill.	It re–ignites to a flame.	C(in wood) + O2(g)  ==> CO2(g)The relighted splint is mainly combustible carbon.
Chemical test for HCl hydrogen chloride gas, in water forms hydrochloric acid.Note that HCl does NOT bleach litmus paper like chlorine does.	(i) Damp blue litmus.(ii) Apply a drop ofsilver nitrate on the end of a glass rod	(i) Litmus turns red(ii) A white precipitate.	(i) Strongly acid gas.(ii) In water forms chloride ions – hence precipitate with silver nitrate, see chloride test.
chemical test for hydrogen bromideHBr and Hydrogen iodide HI	As above. In water they are hydrobromic acid and hydriodic acid.	as above but cream precipitate with HBr or yellow precipitate with HI.	As above – combination of acid and halide ion tests.
Chemical test for sulphur dioxide gas SO2  (sulfur dioxide, sulphur(IV) oxide, sulfur(IV) oxide)	Freshly made potassium dichromate(VI) paper.	paper changes from orange to green.	The orange dichromate(VI) ion, Cr2O72–(aq)is reduced to the green Cr3+(aq) ion.
Chemical test for ammonia gas NH3Strong pungent odour.*	(i) Damp red litmus. (ii) Near fumes of conc. hydrochloric acid.	(i) Litmus turns blue.(ii) Gives white cloudswith HCl fumes.	(i) Ammonia is the only common alkaline gas.(ii) It forms fine ammonium chloride crystals with HCl. (*volatile organic aliphatic amines give the same result, and smell more fishy)
Chemical test for bromine Br2 (l or aq)A dark red liquid – orange–brown fumes, yellow–orange aqueous solution. The other common orange–brown gas is nitrogen dioxide	(i) Shake with a liquid alkene.(ii) Mix with silver nitrate solution.	(ii) Decolourised. See alkene test.(ii) Cream ppt. of silver bromide. See bromidetest.	(i) Forms a colourless organic dibromo–compound>C=C< + Br2 ==> >CBr–CBr< (ii) Ag+(aq) + Br–(aq) ==> AgBr(s)   Any soluble bromide gives a silver bromide precipitate.
Chemical test for chlorine gas Cl2A pungent green gas. Test (ii) on its own is no good, could be HCl, but hydrogen chloride does not bleach litmus paper.	(i) Apply damp blue litmus. (Can use red litmus and just see bleaching effect.)(ii) A drop silver nitrate on the end of a glass rod into the gas.	(i) litmus turns red and then is bleached white.(ii) White precipitate.	(i) Non–metallic chlorine is acid in aqueous solution and a powerful oxidising agent which is why you get the double colour change.(ii) It forms a small amount of chloride ion in water, so gives a positive result for the chloride test.
Chemical test for iodine (i) solid or (ii) solutionA dark coloured solid.	(i) Gently heat the solid.(ii) Test aqueous solution or solid with starch solution.	(i) Gives brilliant purple vapour.(ii) A blue black colour.	(i) Iodine forms a distinctive coloured vapour and note it sublimes – changes directly from a solid to a gas–vapor.(ii) Forms a blue–black complex with starch and in biology the test is used to detect starch with iodine solution.
Chemical test for hydrogen sulphide H2S (hydrogen sulfide)	Test gas with damp lead(II) ethanoate paper (old name lead acetate).	Rotten egg smell of hydrogen sulphide gas and the H2S gas turns lead(II) ethanoate paper black.	Hydrogen sulphide gives sulphide ions in water, soPb2+(aq) + S2–(aq) => PbS(s)  The gas is formed when acids react with sulphides.
Chemical test for nitrogen(IV) oxide  nitrogen dioxide NO2	There is no simple relatively unambiguous test. The other common orange–brown gas is bromine.	Its a nasty orange–brown gas	Its a strong oxidising agent. Dissolved in water it gives a solution of nitrite and nitrate ions. The other common brown gas is bromine and the solution of nitrogen dioxide shouldn't give a cream ppt. with silver nitrate solution.
Chemical tests for waterliquid H2OEasy to get these colour changes muddled!	(i) Add a few drops to white anhydrouscopper(II) sulphate.(ii) Dip in a piece of dry blue cobalt chloride paper.	(i) Turns from white toblue.(ii) Turns from blue to pink.	(i) Blue hydrated copper(II) crystals or solution formed(ii) Pink hydrated cobalt ion formed [Co(H2O)6]2+