As part of my school project I'm currently investigating the effect of temperature on vitamin C concentration (in a solution I made) using iodine titration but when I tried my experiment today I kept getting different values for the same solution. Any ideas why this might have happened?
Details of my methodology:
I dissolved a certain amount of crushed vitamin C tablet into distilled water to make a standard solution. I stored this solution in a refrigerator (that shuts off the lights inside when the door is closed) to control the light and temperature when the solution was not in use. I used an iodine solution that I made from potassium iodide and iodine as well as a 1% starch indicator solution for titration. I added the starch indicator to a 25 mL aliquot of the vitamin C solution then titrated it with the iodine solution until endpoint. To vary the temperature, I heated the vitamin C solution on a hot plate to the desired temperatures (25, 40, 50, 60, 70 degrees celsius). Should I change how I'm heating the solution? A water bath for longer temperatures?