Science Buddies: "Ask an Expert"

I was doing the Project "Which Orange Juice Has The Most Vitamin C" and I was on the step of titrating a vitamin c standard solution and I followed all the steps. But when I was using the burette to titrate the vitamin standard with the added ten drops of starch solution.
But every time I tried no color would change to a bluish-black in the beaker.
I think that maybe I need to use 10 drops of the vitamin standard instead of the starch solution and pour 20ml of starch solution instead
WHat do you think???

Hello, Krishan,

If you were doing all the steps for titrating the standard solution correctly, there might be something wrong with the Vitamin C solution itself. Remake it and try the titration again. If it works, then you'll know why! If it doesn't and you're still having problems, write back about what exactly happened, and I'll help you from there.

Thank You
It did work after making the vitamin c solution as well as the starch which might have not dissolved as well the first time

Help! We are on our 4th attempt to just get our standard titration number. We have diluted the starch 5 times. We have dropped iodine 4 different times, as many as 300 times in one attempt. I have double checked the iodine to see if it was diluted correctly.It is. We have yet to get a blue color change. The Vit C tablet has been crushed and diluted 4 times. I have checked that dilution as well.

Hi ConnieBush,

I'm sorry to hear that you are having problems with your titration. It can very, very frustrating. Can you please post a link to the specific procedure you are using?

Have you tried the suggestions on this page?

https://www.sciencebuddies.org/science- ... l#overview

Note that the article has several tabs, each with more information (e.g., indicators, setup and procedure, interpreting results).

Here are some other questions that might help you find the trouble spot.

When doing the titration, how slowly did you add the drops of iodine solution? If you add the solution too quickly, you might miss the endpoint of the titration. It's best to go slowly, 1 drop at a time, swirling the flask after each drop. It can be tedious, but overshooting is a very common problem with titrations.

Did you rinse the burette with the transferred solution before filling it and starting to titrate? If the most recent thing in the burette was water, water clinging to the inside of the burette can dilute the solution.

Did all of the vitamin C tablet dissolve?

Is it possible that either the starch solution or iodine solution have been contaminated by something else?

Any other details that you can provide about your setup would be helpful for helping us troubleshoot with you.

Great project. If you need anymore help, ask me. I'm a very technical person with a brilliant mind and i will make your project hit the top charts. So, Kaiden, if you need help, contact me ASAP.
Sincerely yours,
Vicotria Kendall Lee