Your question is a very good one, and important for a science fair project. Paying attention to these details and carefully explaining the science behind your project will make the difference in winning an award at a science fair. I assume you will be testing a number of samples for vitamin C content. The first thing the judges will be interested in is the purpose of your experiment. Can you explain why you want to measure vitamin C in your samples, or why you wanted to do this project? This is your purpose, so write a sentence or two telling the judges why you did the project. Next, what is your hypothesis? This is your guess (based on your background research) of what will happen in your experiment. (If you can reply with this information, we can make comments that might help improve the scientific presentation.)
Next, you want to give some background information. I would suggest writing one paragraph about the history and importance of vitamin C. Here are some websites that have additional information:
You will also explain how vitamin C can be measured with the starch-iodine test in this section. So write a paragraph describing how vitamin C is measured.
This site has a nice picture showing the structure of a starch molecule, and shows how iodine (an element) interacts with the starch to form a blue complex.
http://www.elmhurst.edu/~chm/vchembook/ ... odine.html
Now, hereâ€™s the part that I think is confusing to you. The actual basis of the reaction is a chemical reaction called a reduction/oxidation, or redox reaction. Hereâ€™s a website that explains the chemistry of this reaction.
Since you havenâ€™t had chemistry yet, the judges will not expect you to completely understand this, but you should try to explain this as well as you can. I think it would be sufficient if you just explain that the reaction is due to the vitamin C transferring electrons (do you know what an electron is?) to the iodine. As you add iodine to the sample with vitamin C, the iodine takes electrons from the vitamin C and when it has extra electrons, it cannot form the blue complex with the starch. When all of the vitamin C is gone, there is extra iodine available to combine with the starch, and you can see this because the blue/black color appears. The amount of vitamin C in the sample is proportional to the amount of iodine you have added to the sample. Samples with higher vitamin C content will require more iodine to be added.
Next, list all of the items you used for the samples and the testing.
Hereâ€™s a site that describes how to make the starch and iodine solutions:
http://www.accessexcellence.org/AE/ATG/ ... acher.html
This next site shows pictures of the steps used to titrate vitamin C. I recommend taking pictures of your experimental set-up to show the judges how you did your testing. If you canâ€™t take pictures, write a detailed step-by-step description of how you did your titration (e.g. how you measured the volume of iodine required until blue color appeared).
http://biology.clc.uc.edu/fankhauser/La ... tocol.html
I hope this isnâ€™t too confusing for you, but if you go through step-by-step, youâ€™ll have all of the information you need for the first few sections of your board. You can use the websites for your references, but some teachers require a non-website source, so you may need to find a book with some information related to your project. Youâ€™ll just have the results and conclusions sections to complete.
Now, do you need any suggestions on your experimental design? Or, have you done your experiment and do you need help writing up your results. You definitely want to measure the volume of iodine you use for each sample and graph your results. If you will post some details about your experiment, we can give more specific suggestions.