Potassium Thiocyanate

Potassium Thiocyanate solution can be used in titrations involving Silver Nitrate solutions. Chloride, Bromide and Iodide can be determined indirectly this way by adding excess Silver Nitrate solution to the sample containing the Halide, thus precipitating the Halide, and titrating the excess Silver Nitrate with Potassium Thiocyanate titrant using a Ferric Alum Indicator. 

The reactions for this Volhard titration are:

X- + excess AgNO3 → AgX (precipitate) + AgNO3
X = Cl, Br, I

KSCN + AgNO3 → AgSCN (white precipitate) + KNO3

excess SCN- + Fe3+ → [FeSCN]2+ (red complex at endpoint)

Potassium Thiocyanate solution can also be used to standardize Mercuric Nitrate solutions using Ferric Alum as the indicator:

2 KSCN + Hg(NO3)2 → Hg(SCN)2 (white precipitate) + 2 KNO3

excess SCN- + Fe3+ → [FeSCN]2+ (red complex at endpoint)

Ammonium Thiocyanate and Potassium Thiocyanate solutions can be used interchangeably in these determinations.