50ml sample was placed in a 500 ml refluxing flask. 5 to 7 glass boiling beads was added to serve as antibumping
aid followed by the addition of 1g of mercury (II) tetraoxosulphate (VI) (HgSO4) crystal. 5 ml of
concentrated tetraoxosulphate (VI) acid (H2SO4)/silver (I) tetraoxosulphate (VI) solution (Ag2SO4) was added,
and mix until the HgSO4 was in solution. The function of HgSO4 is to bind or complex chlorides. 1 g may not be
required if the chloride concentration is low (Caution: Always add acid slowly down the side of the flask while
mixing to avoid over-heating. It may be necessary to use gloves because of the heat generated).
Accurately measured 25 ml of 0.25N potassium heptaoxochromate (VI) (K2Cr2O7) was added and mixed; while
mixing, an additional 70 ml of concentrated H2SO4-Ag2SO4 solution was added. After thorough mixing, the flask
was attached to the reflux condenser; the mixture was gently heated in a water bath, and reflux for 2 h. The
apparatus was then cooled to room temperature after the refluxing period. Washing down of the interior of the
condenser and flask twice, with approximately 25 ml portions of distilled water was carried out. The flask was
removed from the condenser and diluted to a final volume of approximately 350 ml with distilled water and,
further cooling was done with running tap water. 2 to 3 drops of Ferroin indicator was added and stirred with a
magnetic stirring bar. The resulting mixture was rapidly titrated with 0.1 N iron ((II) ammonium tetraoxosulphate
(VI)-6-water, FeSO4(NH4)2SO4.6H2O, to the first red-brown endpoint (Caution: Use care in titration. The
endpoint is very sharp and may be reached rapidly). The same procedure was repeated for other samples.