testing vitamin c

[cutie_gabby]

how does iodine and starch test vitamin c in different juices

[donnahardy2]

Hi Gabby,

I'm assuming you haven't had a class is chemistry yet, so here is a very basic explanation. Starch and iodine will react with each other to give a dark blue complex. Vitamin C will react with iodine by giving it extra electrons and the converts it to iodide. Iodide ions do not react with starch to give a blue color.

So here is how the vitamin C assay works. When you are testing a sample, you have to keep adding iodine to the sample until there is an excess of iodine left to react with the starch. The appearance of the blue color indicates there is no vitamin C left in the sample to react with the iodine. So the concentration of vitamin C in the sample is proportional to the amount of iodine you added, and you can plot your results on a graph.

Let me know if you need more details about the reaction.

Donna Hardy

[cutie_gabby]

thanks for your help. do you know what the colors stand for? i really need help on this project and how to do it can you please get back to me with advice. i would really appreciate it. and can you tell me where to get the iodine and starch here in fresno ca? thank you.

[donnahardy2]

Hi Gabby,

You can buy cornstarch in the grocery store. You can check with your local pharmacy or feed store for iodine. I have had good luck with Walgreen's pharmacy; they have ordered special chemicals for me that are not normally stocked. If the iodine is not available for purchase locally, you will have to purchase from a scientific supply company, but it will be more expensive. Here is one website:

http://www.sciencestuff.com/prod/Chem-Rgnts/C1905

For a local supplier in Fresno, you might try:

http://www.fresnoscientificinc.com/

Good luck!

Donna Hardy

[donnahardy2]

Hi Gabby,

I forgot to answer your question on color. When a starch solution is mixed with iodine, a blue complex is formed. For a vitamin C experiment, you will have starch in your sample, so a blue color indicates that iodine is present. Vitamin C oxidizes, or adds electrons to iodine molecules to form iodide ions and iodide does not form a blue complex with starch. The blue color will appear when you titrate your sample as soon as there is a slight excess of iodine in the sample. The amount of iodine you add to your sample is directly proportional to the amount of vitamin C in the sample.

For your experiment, you might want to plot concentrations of vitamin C from samples containing a known concentration (y axis) vs. ml of iodine (x-axis). You can then use the standard curve to quickly determine the concentration of vitamin C in your sample, provided the sample falls within the range of your standard curve.

Please let us know if you need more help on this project, or if you need additional explanation about the chemistry of the reaction.

Donna Hardy

[cutie_gabby]

thank you for the advice and uuuum... well what info should i use for my review of literature?????? Can you explain more to me about what iodine has in it to make the vitamin c or the juice change colors. thank you[/b] and how do i type to u u never have any posts????

[donnahardy2]

Hi Gabby,

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:

http://www.garynull.com/Documents/vitaminc.htm
http://home.howstuffworks.com/vitamin-c.htm

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, here’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. Here’s a website that explains the chemistry of this reaction.

http://paws.wcu.edu/bacon/Vitamin%20C.pdf

Since you haven’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.

Here’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 can’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 isn’t too confusing for you, but if you go through step-by-step, you’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. You’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.

Donna Hardy

[donnahardy2]

Hi Gabby,

How are you doing? What the information I posted too complicated? Do you still need some help? We want you to have a great project. Let me know what grade you are in if you do reply.

Donna Hardy

[cutie_gabby]

thank you again for giving greaaaaaaaaaaaaaaaaaaat advice. well since you wanted to know i am only in the sixth grade. thanks for helping i really a[[reciate it. Right now I am pretty caught up with everything so i should be fine. being the president of the school is pretty hard when they expect you to have everything purfect. anyways, if i need any more help i will post another reply thank you soooooo much you're the best!

[cutie_gabby]

oops i meant to say appreciate it not a[[reciate it sorry!!!

[cutie_gabby]

where do i buy my dropper????? i can't find them anywhere!!!!!!!!!!!!!

[donnahardy2]

Hi Gabby,

Where have you looked? Have you tried your local pharmacy (ask the pharmacist)? How about a feed store, pet food store, veterinarian, baby food section of the grocery store, or beauty supply store? You don't actually need a bottle with a dropper. You could use anything that will deliver uniform drops. A soft plastic bottle with a small hole in the top or a syringe would work. Perhaps your teacher could give you a disposable pipette to use. Use your imagination if you can't find exactly what you think you need.

There are about 20 drops in a milliliter. You will be measuring total volume. Whatever you use, use the same dropper source for all of your samples.

Good luck!

Donna Hardy

[Brian121]

Hi Gabby,

I'm assuming you haven't had a class is chemistry yet, so here is a very basic explanation. Starch and iodine will react with each other to give a dark blue complex. Vitamin C will react with iodine by giving it extra electrons and the converts it to iodide. Iodide ions do not react with starch to give a blue color.

So here is how the vitamin C assay works. When you are testing a sample, you have to keep adding iodine to the sample until there is an excess of iodine left to react with the starch. The appearance of the blue color indicates there is no vitamin C left in the sample to react with the iodine. So the concentration of vitamin C in the sample is proportional to the amount of iodine you added, and you can plot your results on a graph.

Let me know if you need more details about the reaction.

Donna Hardy

My friend the real fact of Vitamin C is the benefit was only seen when those foods were included in the diet; no benefits were seen with supplements of vitamin C or E. I saw a results which underline the importance of evaluating the complex inter-relationships between antioxidants. My family doctor told me that "A diet rich in vegetables, berries and fruits contains a large variety of bioactive compounds that may also synergistically contribute to antioxidative and immunomodulatory effects. There appears to be no short cut in reducing the risk of atopic and other chronic diseases; a healthy balanced diet may outweigh the use of single dietary supplements."

[maymay]

I am doing this same experiment. I just started practicing it today. Most sites told me to add the iodine to the starch and then add the juice drop by drop but it was too hard since the juice was colored to figure out when the blue color went away. I saw another site that said to do it the way you described. How long should I wait before saying the color has changed? If I think it has happened and leave the room for awhile, I come back, and it's back to the same color I started with. Is there some sort of time limit rule? I don't understand why this happens, and I wonder if the numbers I will record will be right?

[jamestheconfused]

Hello there,

I am really confused by this whole project with the vitamin C thing. What is a starch solution????? I was told it was baking soda with water but it never mixed properly so the whole this was a flop! Please help and tell me what a starch solution is.[/b]