# Qualitative analysis of inorganic compounds

The experimental details given here are given in good faith and are believed to be safe and workable methods. However, the authors cannot take responsibility for the consequences of performing these experiments.
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 | solid dissolves - effervescence occurs - a colourless gas given off that turns limewater milky. | CO$_2$ given off. X contains carbonate ions CO$_3$$^{2-}$. |
| | solid dissolves - effervescence - a pungent colourless gas that turns acidified dichromate green. | SO$_2$ given off. X contains sulphite ions SO$_3$$^{2-}$ |
| | solid dissolves - effervescence occurs - a colourless gas given off that gives characteristic pop with a lighted splint. | H$_2$(g) given off. X is a metal. X could be aluminium , zinc, iron, tin or magnesium |
| X(aq) + sodium hydroxide | white ppt. - soluble in excess. | 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$^{2+}$. |
| | reddish brown ppt. - insoluble in excess. | Iron (III) hydroxide, Fe(OH)$_3$ formed. X contains iron (III) ions, Fe$^{3+}$. |
| | dirty green ppt. - insoluble in excess. Slowly turns reddish brown where exposed to air. | iron (II) hydroxide, Fe(OH)$_2$ formed. X contains iron (II) ions, Fe$^{2+}$. |
| | blue ppt. - insoluble in excess. | copper (II) hydroxide Cu(OH)$_2$ formed. X contains Copper (II) ions Cu$^{2+}$. |
| | light brown ppt. - darkens on standing. | manganese (II) hydroxide formed. Mn(OH)$_2$. X contains manganese (II) ions Mn$^{2+}$ |
| X(s) + sodium hydroxide .Warm | Pungent colourless gas given off - turns moist red litmus blue. White fumes formed with conc. HCl | The gas is ammonia NH$_3$. X(s) contains ammonium ions NH$_4$+ |
| X(aq) + aqueous ammonia (ammonium hydroxide) | white ppt. - insoluble in excess. | aluminium hydroxide Al(OH)$_3$ or Pb(OH)$_2$. X contains Al$^{3+}$ or Pb$^{2+}$ |
| | white ppt. - soluble in excess. | Zinc hydroxide Zn(OH)$_2$ formed. X contains Zn$^{2+}$. |
| | reddish brown ppt. - insoluble in excess | Iron (III) hydroxide formed; Fe(OH)$_3$. X contains iron (III) ions, Fe$^{3+}$ |
| | dirty green ppt. - insoluble in excess. Slowly turns reddish brown where exposed to air. | Iron (II) hydroxide, Fe(OH)$_2$ formed. X contains iron (II) ions, Fe$^{2+}$ |
| | blue ppt. - dissolves in excess to form a deep blue solution. | copper (II) hydroxide Cu(OH)$_2$. complex ion formed. X contains Cu$^{2+}$. |
| | no ppt. formed but the solution becomes a different colour. | transition metal complex ion formed. X contains a transition metal ion. |
| X(aq) + barium chloride (or nitrate). | white ppt. - insoluble in excess. | barium sulphate formed. BaSO$_4$. X contains sulphate ions SO$_4$$^{2-}$. |
| X(aq) + chlorine solution | yellow or reddish brown colouration | Bromine Br$_2$ or iodine I$_2$ formed |
| | turns tetrachloromethane purple. | Iodine I$_2$ formed. X contains iodide ions I$^-$ |
| | turns tetrachloromethane orange or yellow | bromine Br$_2$ formed. X contains Bromide ions Br$^-$ |
| X(aq) + lead nitrate or lead ethanoate | bright yellow ppt. - insoluble in excess | lead (II) iodide, PbI$_2$; or lead (II) chromate, PbCrO$_4$, formed. X contains iodide ions I$^-$ or chromate ions CrO$_4$$^{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 | lead (II) chloride, PbCl$_2$, or lead (II) bromide, PbBr$_2$, formed. X contains chloride ions, Cl$^-$, or bromide ions, Br$^-$. |
| X(aq) + lead (II) nitrate or lead (II) ethanoate | yellow ppt. - soluble in excess. | lead (II) iodide, PbI$_2$, formed. X contains iodide ions I$^-$. |
| X(aq) + potassium iodide | yellow ppt. - soluble in excess. | lead (II) iodide, PbI$_2$, formed. X contains lead (II) ions Pb$^{2+}$. |
| | Yellow or reddish brown colouration produced. | Iodine I$_2$ formed. X is an oxidising agent. |
| X(aq) + potassium manganate (VII) solution (acidified) | purple colouration fades. | permanganate has been reduced.Mn$^{2+}$ formed. X is a reducing agent. |
| X(aq) + potassium dichromate (VI) solution (acidified) | orange solution becomes green or blue/green. | dichromate has been reduced. Cr$^{3+}$ formed. X is a reducing agent. |
| X(aq) acidifed with nitric acid then silver nitrate added. | white ppt. - darkens in bright daylight - soluble in excess dil. ammonia. | silver chloride, AgCl, formed. X contains chloride ions Cl$^-$. |
| | off white creamy ppt. - soluble in excess conc. ammonia. | silver bromide, AgBr, formed. X contains bromide ions Br$^-$. |
| X(aq) + silver nitrate | pale yellow ppt. - insoluble in dil. and conc. ammonia. | silver iodide, AgI, formed. X contains iodide ions I$^-$. |
| X(aq) + sodium carbonate solution. | white ppt. - insoluble in excess. | 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+}$. |
| | dirty green ppt. | copper (II) carbonate, CuCO$_3$ formed. X contains copper (II) ions, Cu$^{2+}$. |
| | effervescence - colourless gas which turns lime water milky. | carbon dioxide formed. X is acidic (produces H$^+$ ions in solution). |
| X(aq) + sodium hydroxide + aluminium and warm | Pungent colourless gas given off - turns moist red litmus blue. White fumes formed with conc. HCl | The gas is ammonia NH$_3$. X(aq) contains nitrate ions NO$_3$- |
| X(aq) + dil. sulphuric acid | effervescence - colourless gas - turns lime water milky. | carbon dioxide formed. X contains carbonate ions CO$_3$$^{2-}$. |
| | white ppt. formed - insoluble in excess | insoluble sulphate formed. X contains ONE of the following : calcium ions Ca$^{2+}$ barium ions Ba$^{2+}$ strontium ions Sr$^{2+}$ lead (II) ions Pb$^{2+}$ |
| X(s) + conc. sulphuric acid. | effervescence - misty white fumes which turn moist blue litmus red. | hydrogen chloride HCl given off. X contains chloride ions Cl-. |
| | effervescence - misty white fumes + orange fumes - blue litmus bleached. | hydrogen bromide HBr and bromine Br$_2$ formed. X contains bromide ions Br-. |
| | effervescence - purple black fumes formed. | iodine I$_2$ formed. X contains iodide ions I- |
| X(s) + conc. hydrochloric acid | Pungent green-yellow gas given off, bleaches litmus paper white. | 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$_2$ |
| | effervescence, colourless gas given, gives a characteristic pop with a lighted splint | hydrogen gas formed H$_2$. X could be aluminium, magnesium , zinc, iron or tin. |
| X (aq) + conc. Hydrochloric acid | White ppt. formed soluble in excess acid | Lead (II) chloride formed. Forms a complex ion PbCl$_4$- with excess conc. hydrochloric acid |

## 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:
| (crimson) Lithium | (yellow/orange) Sodium | (lilac) Potassium | (green/blue) Copper |
| (orange/red) Calcium | (red) Strontium | (apple green) Barium | (white/blue) Lead |

## References

Davies, DG & Kelly, TVG Inorganic Reactions at Advanced Level published by Mills & Boon ISBN 0 263 05692 9