Question

The hexacyanoferrate(III) ion oxidizes Vitamin C (ascorbic acid, `"H"_2"Asc"`) to dehydroascorbic acid (`"Asc"`). What is the concentration of Vitamin C if 43.9 mL of `1.12 × 10^"-4"color(white)(l) "mol/L K"_3"Fe(CN)"_6` oxidizes 32.9 mL of Vitamin C?

Answer 1

The concentration is `7.47 × 10^"-5"color(white)(l) "mol/L"`.

Explanation:

The equations for the redox reaction are:

`2×["Fe(CN)"_6^"3-" + "e"^"-" → "Fe(CN)"_6^"4-"]`
`1×["AscH"_2 → "Asc" + "2H"^"+" + "2e"^"-"`
`stackrel(————————————————————)("2Fe(CN)"_6^"3-" +"AscH"_2 → "2Fe(CN)"_6^"4-" + "Asc" + "2H"^"+")`

1. Calculate the moles of `"Fe(CN)"_6^"3-"`

`"Moles of Fe(CN)"_6^"3-" = "0.0439" color(red)(cancel(color(black)("L Fe(CN)"_6^"3-"))) ×(1.12 × 10^"-4" color(white)(l)"mol Fe(CN)"_6^"3-")/(1 color(red)(cancel(color(black)("L Fe(CN)"_6^"3-")))) = 4.917 × 10^"-6"color(white)(l) "mol Fe(CN)"_6^"3-"`

2. Calculate the moles of `"AscH"_2`

`"Moles of AscH"_2 = 4.917 × 10^"-6"color(red)(cancel(color(black)("mol Fe(CN)"_6^"3-"))) × ("1 mol AscH"_2)/(2 color(red)(cancel(color(black)("mol Fe(CN)"_6^"3-")))) = 2.458 × 10^"-6"color(white)(l)"mol AscH"_2`

3. Calculate the molarity of the `"AscH"_2`

`"Molarity" = "moles"/"litres" = (2.458 × 10^"-6"color(white)(l) "mol")/("0.0329 L") = 7.47 × 10^"-5"color(white)(l) "mol/L"`