Science Buddies: "Ask an Expert"

Hi!
I'm conducting the following titration experiment to determine the amount of vitamin C in orange juice. https://www.sciencebuddies.org/science- ... #procedure

To determine the amount of orange juice, the procedure provides the following equation: Iodine1VitaminC1=Iodine2VitaminC2

I was wondering where that was derived from, and how exactly it determines the vitamin C in the juice. Thank you!

Hello vyu,

In this experiment the iodine added during titration reacts with vitamin C. The ratio between the number of moles of iodine and the number of moles of vitamin C that react is a constant. So you can change the amount (moles) of vitamin C in a test sample but the ratio iodine/vitamin C remains the same.

The equation from the project uses the volume of iodine solution and the mass of vitamin C in place of the number of moles that react. The number of moles of iodine is equal to the volume titrated multipled by the molar concentration of the solution. The solution concentration is constant for titrations 1 and 2 so it cancels out of the equation. The mass of vitamin C divided by its molecular weight is the number of vitamin C moles. The molecular weight is constant it also cancels out of the equation.

I hope this helps. Please ask again if you have more questions.

A. Norman