Oceanography

i. Standardisation of the thiosulphate

(Determination of ‘f’ factor)\

1g of KI and 2 ml of 50% H₂SO₄ are added to an Erlenmeyer flask with a ground stopper containing 150ml of distilled water. It is mixed well and to it 10 ml of potassium hydrogen iodates solution is added. The solution is gently swirled and is allowed to react for 2-4 min for iodine liberation. The iodine so liberated is titrated with thiosulphate solution to a pale stable colour. Now two drops of starch indicator are added and the titration is continued untile the blue colour disappeard. A blank is also run, however, omitting the hydrogen iodate. If ‘v’ is the ml of thiosulphate consumed, then 10-0.04 = f x v x 0.02 and f= 20/v

The mean value of ‘f' is calculate after repeating the titration for three times.