Titration of Potassium Thiocyanate Solution

Because potassium or ammonium thiocyanates are deliquescent, their solutions are usually standardised by titration against standard silver nitrate solution. The latter is usually pipetted into the titration vessel and the thiocyanate solution added from the burette. Iron(IlI) sulphate solution is used as indicator since it forms an intensely red complex with thiocyanate at the end-point. 

Weigh out accurately about 10.5 g purest KSCN, dissolve in water, transfer to a 1 dm volumetric flask and make up to the mark. 

Pipette 25.0 cm of standard 0.1 M silver nitrate solution into a 250 cm flask and add 1 cm of 40% w/v solution of purest ammonium iron(lll) sulphate acidified with nitric acid. Titrate with the thiocyanate solution until the appearance of a faint brown colour in the flocculated suspension of white silver thiocyanate. Repeat and calculate from the average titre [SCN j in mol dm.  

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