$word_{count}$: 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.