2 A. A 5.000 g sample of a Cu(II) s a lt was disso lved in water in a 250 mL fla

Question

2 A. A 5.000 g sample of a Cu(II) s a lt was disso lved in water in a 250 mL flask and diluted to the calibration mark. Then , a 50.00 mL al iquot was analyzed by adding 2.0 g of KI and titrating the liberated I 2 with 29.20 mL of 0.0510 M Na 2 S 2 O 3 using starch indicator. What was the wt% Cu in the copper salt? W t % Cu _______________ 4

2B. S hould starch indicator be added to this titration at the beginning of the titrati on or just before the equivalence point i s reached? Explain your answer.

Explanation / Answer

2B ) The Starch indicator is added just before end point becouse addition neat end point avoids formation of excess Starch-iodine complex which would be difficult to decompose. It also gives the sharp end point.

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