Ammonium Thiocyanate

Ammonium Thiocyanate
Chemical Formula NH4SCN
Formula Weight 76.12
Equivalent Weight 76.12 (Molar = Normal)
CAS No. 1762-95-4

Ammonium 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 Ammonium Thiocyanate titrant using a Ferric Alum Indicator. The reactions for this Volhard titration are:

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

NH4SCN + AgNO3 → AgSCN (white precipitate) + NH4NO3

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

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

2 NH4SCN + Hg(NO3)2 → Hg(SCN)2 (white precipitate) + 2 NH4NO3

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

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