Why does NBS turn sodium thiosulphate solution yellow?

For my A2 coursework I am finding out the concentration of vitamin C in lemon juice. I am using two methods - titration with NBS
(N-bromosuccinimide) and colorimetry. In preparation for colorimetry, I am standardising iodine solution with sodium thiosulphate solution. Somehow, I contaminated the burette containing sodium thiosulphate solution with a tiny bit of NBS solution :redface:

and the thiosulphate solution turned from colourless to a nice banana colour! Can anyone explain why this happened?

Thank you!

Reply 1

Shahida

is that experiment easy to do?

Reply 2

TaZ

Yes it's quite easy. The NBS titration is no problem and NBS can easily be standardised with pure ascorbic acid dissolved in water. I haven't started the colorimetry yet so i can't say about that!