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Qualitative Analysis: Salt Analysis revision notes

Every idea in the Qualitative Analysis: Salt Analysis chapter for JEE Main, with the usual mistakes and the fast methods. Topic 1 is open to everyone; sign in free to read all 18 and download the PDF.

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How we count: 7× asked means 7 past JEE Main questions in the PrepWiser bank needed that concept, and "last" is the latest year one appeared. ★ marks ideas asked 8 or more times.

Preliminary tests: colour, flame, borax bead

Flame test
4× asked, last 2026
Na golden yellow,K lilac (violet),Ca brick redSr crimson red,Ba apple green,Cu green with blue centre\begin{gathered}\ce{Na}\ \text{golden yellow},\quad \ce{K}\ \text{lilac (violet)},\quad \ce{Ca}\ \text{brick red}\\ \ce{Sr}\ \text{crimson red},\quad \ce{Ba}\ \text{apple green},\quad \ce{Cu}\ \text{green with blue centre}\end{gathered}
Salt made into a paste with conc. HCl on a Pt wire: chlorides are volatile. Excited electrons emit light of a set colour.
golden yellowNalilac (violet)Kbrick redCacrimson redSrapple greenBagreen, blue centreCu
Flame colours on the sheet (Mg, Zn, Fe, Co, Ni give none)
  • Not every cation colours the flame. MgX2+\ce{Mg^{2+}} (electrons too strongly bound), ZnX2+\ce{Zn^{2+}}, FeX2+\ce{Fe^{2+}}, CoX2+\ce{Co^{2+}} and NiX2+\ce{Ni^{2+}} give none. Usable colours: alkali metals, Ca, Sr, Ba and Cu.
Borax bead test
5× asked, last 2025
NaX2BX4OX7 ⋅ 10 HX2O→Δ2 NaBOX2+BX2OX3+10 HX2O,CuO+BX2OX3→Cu(BOX2)X2O-flame (hot/cold): Cu green/blue, Fe yellow-brown/yellow, Cr yellow/green, Ni violet/red-brownMn violet, Co blue;R-flame: Cu red (metal), Fe and Cr green, Ni grey, Co blue\begin{gathered}\ce{Na2B4O7.10H2O ->[\Delta] 2NaBO2 + B2O3 + 10H2O},\qquad \ce{CuO + B2O3 -> Cu(BO2)2}\\ \text{O-flame (hot/cold): Cu green/blue, Fe yellow-brown/yellow, Cr yellow/green, Ni violet/red-brown}\\ \text{Mn violet, Co blue;\quad R-flame: Cu red (metal), Fe and Cr green, Ni grey, Co blue}\end{gathered}
Glassy bead on a Pt loop. O = non-luminous (oxidising) flame, higher state; R = luminous (reducing) flame. Coloured ions only.
O-flame, hotO-flame, coldR-flameCugreenbluered (metal)Feyellow-brownyellowgreenCryellowgreengreenNivioletred-browngreyMnvioletvioletnot listedCoblueblueblue
Bead colours as the sheet gives them (O = oxidising, R = reducing flame)
  • Two ions are violet in the oxidising flame: MnX2+\ce{Mn^{2+}} (hot and cold) and NiX2+\ce{Ni^{2+}} (hot only; reddish-brown cold).
  • Not colourless cupric metaborate. Blue-green Cu(BOX2)X2\ce{Cu(BO2)2} is the oxidising-flame product. The luminous (reducing) flame gives colourless cuprous CuBOX2\ce{CuBO2}, then red Cu metal.
Also remember
  • Hydrated salt or solution: CuX2+\ce{Cu^{2+}} blue, NiX2+\ce{Ni^{2+}}, FeX2+\ce{Fe^{2+}} green, FeX3+\ce{Fe^{3+}} yellow-brown, CoX2+\ce{Co^{2+}}, MnX2+\ce{Mn^{2+}} pink. d0d^0, d10d^{10} ions (AlX3+\ce{Al^{3+}}, CaX2+\ce{Ca^{2+}}, ZnX2+\ce{Zn^{2+}}): white.
  • Charcoal cavity: MSOX4\ce{MSO4} + NaX2COX3\ce{Na2CO3} gives MO. Carbon reduces easy oxides (PbO, CuO) to metal; ZnO, AlX2OX3\ce{Al2O3}, MgO stay as a white residue. Cobalt nitrate on it: ZnO green, AlX2OX3\ce{Al2O3} blue, MgO pink.
  • Anhydrous salts can differ from the hydrated colours: CuSOX4\ce{CuSO4} is white, while CuSOX4 ⋅ 5 HX2O\ce{CuSO4.5H2O} is blue because its water ligands split the Cu d levels.

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Practise Qualitative Analysis: Salt Analysis

16 more concepts in 5 topics

Anions: dilute H₂SO₄ group, Anions: conc. H₂SO₄ group and sulphate, Cation groups and why they separate, Confirmatory tests for cations and Colours of precipitates. Read the first part free. Sign in free with Google to read the rest and download the PDF.

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Anions: dilute H₂SO₄ group

  • Gas evolved and its test5×
  • Confirming sulphide, nitrite and acetate4×

Anions: conc. H₂SO₄ group and sulphate

  • Vapours with conc. H₂SO₄4×
  • Chromyl chloride test: Cl⁻ only3×
  • Silver nitrate and layer tests2×
  • Brown ring test: NO₃⁻4×
  • Sulphate, sulphite and phosphate5×

Cation groups and why they separate

  • Group reagents in order8×
  • Common-ion control of precipitation2×

Confirmatory tests for cations

  • Group 0: NH₄⁺ and Nessler's reagent5×
  • Group I: Pb²⁺4×
  • Group II: Cu²⁺6×
  • Group III: Fe³⁺ and Al³⁺5×
  • Group IV: Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺12×
  • Groups V and VI: Ba²⁺, Sr²⁺, Ca²⁺, Mg²⁺6×
  • Also remember2

Colours of precipitates

  • Common precipitates by colour10×

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