Question

Hi I need help with my chemistry problem. You have 50 ml of a drink with 100 mg/liter of vitamin c. How many ml of iodine solution (5% w/v) do you need to react with the vitamin c in the sample? Thank you so much for your help Karen

Answer 1

You need 140 mL of the iodine solution.

Explanation:

Step 1, Calculate the mass of Vitamin C

`"Mass of VitC" = 50 color(red)(cancel(color(black)("mL drink"))) × "100 mg VitC"/(1000 color(red)(cancel(color(black)("mL drink")))) = "5.00 mg Vit C"`

Step 2, Calculate the moles of Vitamin C

`"Moles of VitC" = 5.00 color(red)(cancel(color(black)("mg VitC"))) × "1 mmol VitC"/(176.12 color(red)(cancel(color(black)("mg VitC")))) = "0.0284 mmol Vit C"`

Step 3, Calculate the moles of `"I"_2`

The equation for the reaction is

`underbrace("C"_6"H"_8"O"_6)_color(red)("Vitamin C") + "I"_2 → underbrace("C"_6"H"_6"O"_6)_color(red)("dehydroascorbic acid") + "2I"^"-" + "2H"^"+"`

`"Moles of I"_2 = 0.0284 color(red)(cancel(color(black)("mmol Vit C"))) × "1 mmol I"_2/(1 color(red)(cancel(color(black)("mmol VitC")))) = "0.0284 mmol I"_2`

Step 3, Calculate the mass of `"I"_2`

`"Mass of I"_2 = 0.0284 color(red)(cancel(color(black)("mmol I"_2))) × "253.81 mg I"_2/(1 color(red)(cancel(color(black)("mmol I"_2)))) = "7.21 mg I"_2 = "0.007 21 g I"_2`

Step 4, Calculate the volume of `"I"_2`

`"Volume of I"_2 = "0.007 21" color(red)(cancel(color(black)("g I"_2))) × "100 mL I"_2/(5 color(red)(cancel(color(black)("g I"_2)))) = "0.14 mL I"_2`

Note: The answer can have only one significant figure because that is all you gave for the concentration of the iodine solution.

However, I calculated the volume to two significant figures.