To clarify, a redox titration was performed in which starch was used as an indicator. The purpose of the titration was to determine the concentration of ascorbic acid in various substances such as orange juice. You know the titration is complete when the solution turns into a blue-black colour, meaning that all of the ascorbic acid in the solution has been reacted with and what's left for the excess iodine to react with is the starch indicator. My question is, why does the iodine react with vitamin C before it reacts with the starch? Specifically looking for answers relating to the properties of ascorbic acid and starch as I need to explain this concept within a lab report. Any help would be appreciated, thanks!