Please explain how to solve these problems. Thanks! Calculate the molar concentr

Question

Please explain how to solve these problems. Thanks!

Calculate the molar concentration of an iodate solution prepared by dissolving 1.99 g of KIO3 and diluting to volume with distilled water in a 1000-mL volumetric flask. Calculate the molar concentration of a thiosulfate solution from the following information: A 30.-mL aliquot of a 0.0264 M KIO3 solution is added to a flask containing 2 g of KI and 10 mL of 0.5 M H2SO4. The resulting solution is titrated to a starch endpoint with 31 mL of the thiosulfate solution. Calculate the weight percent of ascorbic acid in a tablet of Vitamin C from the following data: A 100 mg sample of a crushed Vitamin C tablet was dissolved in 40 mL of H2SO4 and 20 mL of water. Two grams of KI and 25 mL of 0.0139 M KIO3 solution was added, and the mixture titrated to a starch endpoint. The titration required 19 mL of 0.0590 M thiosulfate solution. Weight = %

Explanation / Answer

1)

moles = 1.99/214 = 9.3 m moles

molarity = 9.3/1000 = 9.3x10-3 M

2)

KIO3 + 5 KI + 3 H2SO4 = 3 K2SO4 + 3 H2O + 2 I3

moles of KIO3 = 0.792 mmoles

moles of KI = 2/166 = 12 m moles

remaing moles of KI = 12-5*0.792 = 8.04

moles of I2 = 2*0.792 = 1.584

moles of I3-  = 1.584

molarity of thiosulphate = 1.584/31 = 0.05 M

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