0.1N SODIUM THIOSULPHATE (Na2S2O3.5H2O, Eq. Wt. 248.19)
a) WEIGH EXACTLY 24.819 Gms. OF SODIUM THIOSULPHATE AND DISSOLVE IT IN 1000 ML OF DISTILLED WATER BY USING MEASURING FLASK.
b) STADARISATION WITH POTASSIUM DICHROMATE (K2Cr2O7, Eq. Wt. 294.19)
PREPARE 0.1N POTASSIUM DICHROMATE SOLUTION BY
DISSOLVING 1.22575 GM OF POTASSIUM DICHROMATE IN 250ML OF DISTILLED WATER. TAKE
25ML OF THIS SOLUTION WITH 18ML OF 10% KI SOLUTION (10gm KI DISSOLVED IN 90ml
OF DISTILLED WATER) AND 5ML OF CONCENTRATED HCl AND TITRATE AGAINST ABOVE
PREPARED SODIUM THIOSULPHATE SOLUTION BY USING 2% STARCH SOLUTION AS AN
INDICATOR. END POINT IS BLUE TO GREENISH BLUISH. (IF THE SOLUTION IS KEPT FOR
MORE DAYS, ADD 0.1GM NaOH FLAKES OR 3 DROPS OF CHLOROFORM)