PREPARING 0.1N SODIUM THIOSULPHATE (Na2S2O3.5H2O)

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)