Assay –
As per I.P Assay of Sodium Chloride is performed by Modified Volhard’s Method:(I.P.1985)
An accurately specified amount of sample is weighed and dissolved in water, Than it is treated with a known excess of N/10 silver nitrate, concentrated nitric acid, and nitrobenzene. Further the mixture solution is titrated with N/10 ammonium thiocyanate using ferric ammonium sulfate as an indicator. The endpoint indicates the excess silver nitrate after all sodium chloride has precipitated as AgCl. Nitrobenzene helps coagulate AgCl and prevents its interference in titration.
NaCl + AgNO3 ——–> AgCl+ NaNO3+ AgNO3
3NH4SCN+Fe3+ ——–> [Fe(SCN)3] (brick red colour of Ferri thiocyanate)+ NH4+
AgNO3+ NH4SCN—–> AgSCN + NH4NO3
1ml of of 1N AgNO3 = 0.05844gm of NaCl
Procedure-
0.1 gm of Sodium chloride weighed out, dissolve it in 50 ml of water in a stoppered glass flask, add on it 50 ml of0.1 N silver nitrate, 3ml of Nitric acid ,5ml of nitro benzene, 2ml of ferric ammonium sulphate solution and shake well. Titrate it with 0.1 N ammonium thiocyanate untill the colour becomes reddish.
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