3. 24.46 mL of I2 was standardized with a 0.1000 g sample of ascorbic acid. At t

Question

3. 24.46 mL of I2 was standardized with a 0.1000 g sample of ascorbic acid. At the blue starch end point, what is the molarity of the I2 solution?

4. A sample of orange juice was titrated with 0.0286 M I2 solution. A 100 mL sample of juice took 9.89 mL of I2 to reach the starch end point.

a. Write the reaction of vitamin C with iodine.

b. What is the stoichiometric ratio of vitamin C to iodine in the reaction?

c. What is the concentration of the vitamin C in the sample titrated? ( In units of mg VitC/ 100 mL juice).

d. How much of the juice does one need to drink to meet the RDA standard amount of vitamin C for one day?

Explanation / Answer

3)

Ascorbic acid + I2 --> 2 I- + dehydroascorbic acid

   24.46 mL = 0.02446 L

Molar mass of ascorbic acid = 176.12 g / mol

Number of moles in 0.1 g ascorbic acid = 0.1 /176.12

= 0.000567 moles

And,

number of moles of ascorbic acid = number of moles of I2

0.000567 moles = Molarity of I2 * volume

So, Molarity of I2= 0.000567 / 0.02446 L

= 0.0232 M

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