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The test, observation and inference for the identification of NH4+; Ca2+ and Pb2+ ions are presented below.
Test for CationsCations are positively charged ions (atoms or groups of atoms that have more protons than electrons due to having lost one or more electrons). Cations are attracted to negatively charged electrodes... More in Solution using NaOH(aq)
| Test | Observation | Inference |
| Sample solution + NaOH(aq) + heat | A gas with characteristic pungent smell, which turns moist/wet red litmus paper blue, is given off. | Gas is NH3(g) from NH4+. Gas is alkaline. |
| Sample solution + NaOH(aq) – in drops – in excess | White precipitate is formed. Precipitate is insoluble in excess NaOH(aq) | Ca2+ or Pb2+ present Ca2+ present |
| Sample solution + NaOH(aq) – in drops – in excess | White gelatinous is precipitate formed. Precipitate is soluble in excess NaOH(aq) | Zn2+ or Al3+ present |
| Sample solution + NaOH(aq) – in drops – in excess | Powdery/chalky white precipitate formed. Precipitate is soluble in excess NaOH(aq) | Ca2+ or Pb2+ present Pb2+ present |
Test for Cations in Solution using NH3(aq)
| Test | Observation | Inference |
| Sample solution+NH3(aq)- in drops- in excess | No visible reaction | Ca2+ or NH4+ present |
| Sample solution+NH3(aq) – in drops – in excess | White gelatinous precipitate is formed. Precipitate is soluble in excess NH3(aq) Precipitate is insoluble in excess NH3(aq) | Al3+ or Zn2+ present Zn2+ present Al3+ present |
| Sample solution + NH3(aq) – in drops – in excess | White powdery or chalky precipitate is formed. Precipitate is insoluble in excess NH3(aq). | Pb2+ present |
Confirmatory Test for NH4+; Ca2+ and Pb2+ ions
| Test | Observation | Inference |
| Sample solution + NaOH(aq) + warming | No visible reaction. Colourless gas with pungent smell is evolved. The gas turns red litmus paper blue and forms white dense fume with HCl(aq) | The gas is NH3(g) from NH4+ |
| Sample solution + few drops of saturated Na2CO3(aq) or NaHCO3(aq)in drops then in excess | White precipitate is formed. Precipitate soluble in excess Na2CO3(aq) or NaHCO3(aq) | Ca2+ confirmed |
| Sample solution + dil. Or conc. HCl(aq) + heat and allow to cool Sample solution + KI(aq) or K2Cr2O4(aq) | White precipitate is formed.Precipitate dissolved on heating and reappear on coolingYellow precipitate is formed | Pb2+ present Pb2+ confirmed |
| Sample solution + (NH4)2S(aq)Sample solution + Potassium hexacyanoferrate (II) solution (K4(CN)6)(aq) | Dirty white precipitate is formedWhite precipitate is formed | Zn2+ confirmed Zn2+ confirmed |
| Sample solution + NH4OH(aq) followed by NH4Cl(aq) | White precipitate is formed | Al3+ confirmed |
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