1 Qualitative Analysis of Inorganic Compounds Qualitative analysis of inorganic compounds The experiments are written for experienced science teaching staff to use as instructions for a supervised class of students. The experiments are not designed for students or inexperienced members of the public to perform without supervision. If you wish to attempt the experiments, ensure that you have completed a legally adequate risk assessment beforehand and that you work within the constraints of the risk assessment. Test Observation Inference X(s) + dilute acid X(aq) + sodium hydroxide X(s) + sodium hydroxide.warm solid dissolves - effervescence occurs - a colourless gas given off that turns limewater milky. solid dissolves - effervescence - a pungent colourless gas that turns acidified dichromate green. solid dissolves - effervescence occurs - a colourless gas given off that gives characteristic pop with a lighted splint. white ppt. - soluble in excess. reddish brown ppt. - insoluble in excess. dirty green ppt. - insoluble in excess. Slowly turns reddish brown where exposed to air. blue ppt. - insoluble in excess. light brown ppt. - darkens on standing. Pungent colourless gas given off - turns moist red litmus blue. White fumes formed with conc. HCl CO 2 given off. X contains carbonate ions CO 3 2-. SO 2 given off. X contains sulphite ions SO 3 2- H 2 (g) given off. X is a metal. X could be aluminium, zinc, iron, tin or magnesium aluminium hydroxide, Al(OH) 3 ; lead (II) hydroxide, Pb(OH) 2 ; or zinc hydroxide, Zn(OH) 2, formed. X contains one of the following: aluminium ions, Al 3+ ; lead (II) ions, Pb 2+ ; zinc ions, Zn 2+. Iron (III) hydroxide, Fe(OH) 3 formed. X contains iron (III) ions, Fe 3+. iron (II) hydroxide, Fe(OH) 2 formed. X contains iron (II) ions, Fe 2+. copper (II) hydroxide Cu(OH) 2 formed. X contains Copper (II) ions Cu 2+. manganese (II) hydroxide formed. Mn(OH) 2. X contains manganese (II) ions Mn 2+ The gas is ammonia NH 3. X(s) contains ammonium ions NH 4 +
2 Qualitative Analysis of Inorganic Compounds X(aq) + aqueous ammonia (ammonium hydroxide) X(aq) + barium chloride (or nitrate). X(aq) + chlorine solution X(aq) + lead nitrate or lead ethanoate X(aq) + lead (II) nitrate or lead (II) ethanoate X(aq) + potassium iodide white ppt. - insoluble in excess. white ppt. - soluble in excess. reddish brown ppt. - insoluble in excess dirty green ppt. - insoluble in excess. Slowly turns reddish brown where exposed to air. blue ppt. - dissolves in excess to form a deep blue solution. no ppt. formed but the solution becomes a different colour. white ppt. - insoluble in excess. yellow or reddish brown colouration turns tetrachloromethane purple. turns tetrachloromethane orange or yellow bright yellow ppt. - insoluble in excess aluminium hydroxide Al(OH) 3 or Pb(OH) 2. X contains Al 3+ or Pb 2+ Zinc hydroxide Zn(OH) 2 formed. X contains Zn 2+. Iron (III) hydroxide formed; Fe(OH) 3. X contains iron (III) ions, Fe 3+ Iron (II) hydroxide, Fe(OH) 2 formed. X contains iron (II) ions, Fe 2+ copper (II) hydroxide Cu(OH) 2. complex ion formed. X contains Cu 2+. transition metal complex ion formed. X contains a transition metal ion. barium sulphate formed. BaSO 4. X contains sulphate ions SO 4 2-. Bromine Br 2 or iodine I 2 formed Iodine I 2 formed. X contains iodide ions I - bromine Br 2 formed. X contains Bromide ions Br - lead (II) iodide, PbI 2 ; or lead (II) chromate, PbCrO 4, formed. X contains iodide ions I - or chromate ions CrO 4 2- White ppt. - insoluble hot water. lead (II) carbonate PbCO 3 formed. X contains carbonate ions, CO 3 2-. White ppt. - soluble in hot water yellow ppt. - soluble in excess. yellow ppt. - soluble in excess. Yellow or reddish brown colouration produced. lead (II) chloride, PbCl 2, or lead (II) bromide, PbBr 2, formed. X contains chloride ions, Cl -, or bromide ions, Br -. lead (II) iodide, PbI 2, formed. X contains iodide ions I -. lead (II) iodide, PbI 2, formed. X contains lead (II) ions Pb 2+. Iodine I 2 formed. X is an oxidising agent.
3 Qualitative Analysis of Inorganic Compounds X(aq) + potassium manganate (VII) solution (acidified) X(aq) + potassium dichromate (VI) solution (acidified) X(aq) acidifed with nitric acid then silver nitrate added. X(aq) + silver nitrate X(aq) + sodium carbonate solution. X(aq) + sodium hydroxide + aluminium and warm X(aq) + dil. sulphuric acid X(s) + conc. sulphuric acid. purple colouration fades. orange solution becomes green or blue/green. white ppt. - darkens in bright daylight - soluble in excess dil. ammonia. off white creamy ppt. - soluble in excess conc. ammonia. pale yellow ppt. - insoluble in dil. and conc. ammonia. white ppt. - insoluble in excess. dirty green ppt. effervescence - colourless gas which turns lime water milky. Pungent colourless gas given off - turns moist red litmus blue. White fumes formed with conc. HCl effervescence - colourless gas - turns lime water milky. white ppt. formed - insoluble in excess effervescence - misty white fumes which turn moist blue litmus red. permanganate has been reduced.mn 2+ formed. X is a reducing agent. dichromate has been reduced. Cr 3+ formed. X is a reducing agent. silver chloride, AgCl, formed. X contains chloride ions Cl -. silver bromide, AgBr, formed. X contains bromide ions Br -. silver iodide, AgI, formed. X contains iodide ions I -. insoluble carbonate formed. X contains ONE of the following: magnesium ions, Mg 2+ ; calcium ions, Ca 2+ ; strontium ions, Sr 2+ ; barium ions, Ba 2+ ; zinc ions, Zn 2+ ; lead (II) ions, Pb 2+. copper (II) carbonate, CuCO 3 formed. X contains copper (II) ions, Cu 2+. carbon dioxide formed. X is acidic (produces H + ions in solution). The gas is ammonia NH 3. X(aq) contains nitrate ions NO 3 - carbon dioxide formed. X contains carbonate ions CO 3 2-. insoluble sulphate formed. X contains ONE of the following : calcium ions Ca 2+ barium ions Ba 2+ strontium ions Sr 2+ lead (II) ions Pb 2+ hydrogen chloride HCl given off. X contains chloride ions Cl-.
4 Qualitative Analysis of Inorganic Compounds X(s) + conc. hydrochloric acid X (aq) + conc. Hydrochloric acid effervescence - misty white fumes + orange fumes - blue litmus bleached. effervescence - purple black fumes formed. Pungent green-yellow gas given off, bleaches litmus paper white. effervescence, colourless gas given, gives a characteristic pop with a lighted splint White ppt. formed soluble in excess acid hydrogen bromide HBr and bromine Br 2 formed. X contains bromide ions Br-. iodine I 2 formed. X contains iodide ions I- Chlorine gas Cl 2 given off. Solid is an oxidising agent. Red solid could be Pb 3 O 4 Brown solid could be lead (IV) oxide. Black solid could be manganese (IV) oxide MnO 2 hydrogen gas formed H 2. X could be aluminium, magnesium, zinc, iron or tin. Lead (II) chloride formed. Forms a complex ion PbCl 4 - with excess conc. hydrochloric acid
5 Qualitative Analysis of Inorganic Compounds Flame tests A small amount of the unknown substance is added to a quiet blue Bunsen flame. A wire loop, cleaned and moistened with concentrated hydrochloric acid, is used for this purpose. Some metals will colour the flame: (green/blue)copper (crimson) Lithium (yellow/orange)sodium (lilac)potassium (apple green) Barium (orange/red)calcium (red) Strontium (white/blue) Lead
6 Qualitative Analysis of Inorganic Compounds References Davies, DG & Kelly, TVG Inorganic Reactions at Advanced Level published by Mills & Boon ISBN 0 263 05692 9