Determination of water with the Karl Fischer reagent

Determine the end point from the plot of current against volume of iron reagent. Calculate the weight of nitrate ion equivalent to 1.0 mL of the 0.4 M iron solution. 

When dealing with small amounts of nitrate ion it is advisable to pass a current of pure nitrogen through the solution before commencing the titration, and to maintain an atmosphere of nitrogen in the flask throughout the titration. 

If chloride is present, saturated aqueous silver acetate solution should be added in amounts slightly more than the calculated quantity prior t o the addition of concentrated sulphuric acid. The procedure may be applied to the routine analysis of mixtures of nitric and sulphuric acids, and to the determination of nitrogen in esters such as nitroglycerine and nitrocellulose the latter are easily hydrolysed by strong sulphuric acid after dispersal in glacial acetic acid. 

35 DETERMINATION OF WATER WITH THE KARL FISCHER REAGENT 

For the determination of small amounts of water, Karl Fischer (1935) proposed a reagent prepared by the action of sulphur dioxide upon a solution of iodine in a mixture of anhydrous pyridine and anhydrous methanol. Water reacts with this reagent in a two-stage process in which one molecule of iodine disappears for each molecule of water present  

---