Salt Analysis: A Systematic Order for Cation Detection
By Periodic Learn Editorial Team · Published September 24, 2026 · Updated October 15, 2026 · 6 min read
Salt analysis is a logic puzzle, not a memory test. The group reagents are designed to remove possibilities one group at a time, so the order in which you use them is what makes the method work.
Work down the groups, never randomly
Always start by testing the solution with the group reagent for Group I, then Group 2, and so on. If a group gives a precipitate, you test only within that group rather than adding random reagents.
- Group I: dilute HCl precipitates Pb2+, Ag+ and Hg2+ as insoluble chlorides.
- Group 2: pass H2S in acidic medium to precipitate the copper group.
- Group 3: add NH4OH and NH4Cl in basic medium for the aluminium and iron group.
- Later groups: use an excess of ammonium sulfide or carbonate after the earlier groups are removed.
Confirm, do not guess
A precipitate only suggests a group. A flame test, a confirmatory reaction or a specific coloured complex confirms the actual ion. Never report an ion from a single observation.
Common mistakes
- Adding reagents in the wrong order and masking a cation with a precipitate.
- Forgetting to use freshly prepared reagents such as lime water.
- Not acidifying with dilute HCl before passing H2S.
- Ignoring the flame test after a positive group result.