word_count: 210

Fe^2+ tests: Turns K3[Fe(CN)6] (potassium ferricyanide) blue (Turnbull's blue). Brown ring test positive for NO3^- in the presence of Fe^2+.

Fe^3+ tests: Turns K4[Fe(CN)6] (potassium ferrocyanide) blue (Prussian blue). Blood red colour with KSCN (thiocyanate). Both Prussian blue and Turnbull's blue are actually the same compound: Fe4[Fe(CN)6]3.

Cu^2+ tests: Deep blue with excess NH3 ([Cu(NH3)4]^2+). Blue precipitate Cu(OH)2 with NaOH. Black precipitate CuS with H2S.

Cr^3+ tests: Green colour in solution. Chrome yellow PbCrO4 precipitate when converted to CrO4^2-.

Mn^2+ tests: Very faint pink (nearly colourless). Oxidation to purple MnO4^- with PbO2 in HNO3 (confirmatory test).

Ni^2+ tests: Green colour. Red precipitate with dimethylglyoxime (DMG) in ammoniacal solution (very specific test).

Brown ring test: Detects NO3^-. FeSO4 + conc. H2SO4 + nitrate gives brown ring of [Fe(H2O)5NO]^2+ at junction. Fe is in unusual +1 state.

Breathalyser test: Orange K2Cr2O7 turns green (Cr^3+) in presence of ethanol vapour.