Science Buddies: "Ask an Expert"

Hello,

I am working on a Titration of Vitamin C content in orange juice. I used a soluble starch indicator and a Potassium Iodine solution in the titration. The soluble starch was cooled before using. The soluble starch indicator was placed in a conical flask with orange juice and water. The 0.005 mol L^-1 Potassium iodine solution was placed in the burette and slowly dropped into conical flask solution. I tested for vitamin c content of orange juice at room temp, 40, 60, 80, and 100 degrees Fahrenheit. However, for temperatures 60 degrees and higher, I used more potassium iodine to reach the endpoint than room temp and 40 degrees Fahrenheit.

Should it have been less for the 60-100 temps since Vitamin C decreases as temp decreases? Can potassium iodine and starch indicator be used at higher temperatures?

Thanks,
Mary

Hi Mary,

I'm assuming that your titration is similar to the one described in this project:

https://www.sciencebuddies.org/science- ... -c#summary

Did you titrate the orange juice while it was heated to the temperatures listed in your post? If so, I think the higher temperatures may have interfered with the starch indicator.

You might try heating the orange juice to the desired temperature. Then let the juice cool to room temperature before titrating. Repeat for each temperature in your experiment, keeping the heating time constant. In this way, you'd keep the temperature constant for all the titrations and avoid any temperature effects on the indicator.

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

A. Norman