[Vijayalaxmi]

Hello everyone....


Am not able to understand this problem...
Can anyone please tell me the solution...
Its urgent
Please..

A standard solution of potassium iodate was prepared by dissolving 0.1531 g KIO3 in water and diluting to 250.0 mL in a volumetric flask.  10.00 mL of this solution was mixed with excess potassium iodide and the mixture acidified with sulfuric acid.  25.00 mL of fruit juice was added and the mixture titrated with 0.0200 M sodium thiosulfate; 6.33 mL was required.  Calculate the concentration of vitamin C in the fruit juice (assuming no other reducing agents are present).

The reactions involved are:
         IO3-  +  5I-  +  6H+  →  3I2  +  3H2O
         I2  +  C6H8O6  →  2I-  +  C6H6O6  +  2H+
         I2  +  2S2O32-  →  2I-  +  S4O62-

Thank you....

[AWK]

You know an exact mass of iodate, convert it to moles. Then after reaction od 1/25 volume of this solution with iodide you will obtain iodine (IO₃^- ->3I2). since both: Ascorbic acid and thiosulfate react with iodine in the molar ratio 1:1, hence  you can write down this equation:
moles of iodine(known) = moles od thiosulfate (known) + moles of ascorbic acid (unknown).
Finally calculate the unknown concentration of ascorbic acid.