Why don\'t we record the exact mass of potassium iodide used in the titrations?

Question

Why don't we record the exact mass of potassium iodide used in the titrations? If 1.0120 g of potassium iodate were used to make the 500.0 mL solution, what is the molarity of potassium iodate? If 39.98 mL of thiosulfate solution were needed to completely titrate 50.00 ml of potassium iodate from the above solution, what is the concentration of the thiosulfate? How many moles of I_3^- can be generated from 50.00 mL of KIO_3 (from question #2)? If 16.11 mL of standardized thiosulfate (from question #3) is reacted with 50.00 mL of KIO_3 and a portion of a vitamin C tablet, how many moles of I_3^- react with the thiosulfate? How many moles of I_3^- are left to react with the vitamin C? If 14.97% of a vitamin C tablet was used in the above titration (Question #4), how many milligrams of vitamin C does the tablet contain?

Explanation / Answer

1. KIO3 is the limiting reagent, it can be determined by the exact amount of thiosulfate used in the titration. KIO3 is used for the formation of I2.

2, 3, 4, 5 are correct in calculation

6. moles of vitC = moles of I3- reacted = 8.471 x 10^-4 moles

mg of vitamin C = 8.471 x 10^-4 x 176.124 = 0.150 g

14.97% of it = 0.150 x 0.1497 = 22.47 mg

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