Oceanography

ii. Standardisation of sulphide working solution

This is done immediately after the preparation of working solution and colorimetric standard sample. Six Erlenmeyer flasks with ground stoppers are taken and to each of them, 10ml if distilled water, 1-2 g of potassium iodide, 10ml of hydrogen iodate solution and 1 ml of 50% H₂SO₄ are added. For 3 such flasks, 50 ml of sulphide working solution and for the other 3 flasks, 50ml of distilled water are added. All these flasks are kept in a cool place while the colorimetric standardization is commenced and then the contents of the flasks are titrated against thiosulphate using starch indicator.

A=Mean of titrations of three solutions without sulphide solution (ml)

B=Mean of titrations of three solutions with sulphide (ml)

f= factor of thiosulphate

H₂S ml/l = 221.40 x f x (A-B)

                            50

Or

H₂S µg at/ml = 10 x f x (A-B)

                                  50