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?

1 Answer
Apr 2, 2017

Answer:

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"#