Science Buddies: "Ask an Expert"

I have tried The Power of Purple to Evaluate Fats in Cooking Oils multiple times, to no avail. I figured that the iodine I was using was wrong, so I bought the 7% tincture iodine from the link on the experiment page and tried it again. It still didn't work! I don't know what to do. I followed all the directions, so the only think I can think of is that I still don't have the right type of iodine. Actually, I was skeptical that the experiment would work when I saw that the iodine I bought from the link off the science buddies website wasn't purple like the experiment said it would be, but I still tried it anyways. Is the iodine the problem? If so, where can I get iodine that would work for this experiment? Or is there some other easier, faster way to determine the amount of saturated fats in cooking oils? I'm just very frustrated and stressed out by this project, especially since I only have a few days left to finish my science project. Please help!!! Thank you.

Hi,

Will you please describe exactly what happened in your experiment? In the procedure, you are supposed to add the iodine to the heated oil samples until a purple color remains. Please tell me how many drops of iodine you used and what fats you were using and what volume of each oil you used. Did the samples change color at all? Iodine solution is usually a yellowish brown color. What temperature did you use for your experiment?

I’m not quite sure why your experiment with iodine and various oils did not work. Usually solving problems like this depends on understanding the chemistry of the reaction. I have not tried the method described on the Science Buddies website, but I think the reaction should have worked. Iodine reacts with double bonds and substitutes two iodide ions for every double bond. A covalently bonded iodide atom is colorless, so iodine in solution disappears as it is consumed by the double bonds, and the color remains visible when there are no double bonds remaining. The amount of iodine solution that turns colorless is proportional to the number of double bonds in the oil. Here is an explanation of iodine number:

http://www.chemistryexplained.com/Di-Fa ... Acids.html

Here is a formula for preparing iodine solution. You suspect that the iodine solution used may have caused the problem, so perhaps preparing your own solutions from scratch would help identify the problem. Perhaps you could get the ingredients from your high school lab.

http://ibchem.com/IB/ibfiles/organic/or ... _value.pdf

http://en.wikipedia.org/wiki/Iodine_value

However, your project is due on Monday, so if you can’t repeat the experiment with an alternate iodine, try contacting the manufacturer and ask for the formula of the iodine solution you are using. Or, let me know the catalog number and brand of the iodine solution you are using. This information may help provide an explanation of what happened.

Here is some more background information on fat analysis:

http://books.google.com/books?id=JM-R91 ... &q&f=false

You should go ahead and write up your entire project and present the results. You will be graded based on completion of all of the sections, and you do have a complete project including results. You can expand the conclusion section and explain what may have happened in your project, and what you would do if you had more time to do another experiment. Your teacher will appreciate the fact that you have learned some chemistry and are following the scientific method. Here is the information for preparing your display board from the Science Buddies website:

https://www.sciencebuddies.org/science- ... oard.shtml

Be sure to answer all of my questions in the first paragraph when you send a reply.

Donna Hardy

Hi Donna!

Well, first of all the iodine wasn't even purple to start with. When I added the drops (I started with three, I think), the iodine was a yellowish brown color, like you mentioned. I waited for several minutes, but didn't notice any color change at all. And I heated it to about 65 degrees Celcius, like the instructions said.

Hi,

If you were looking for a purple color and only added 3 drops of iodine, it's possible that you didn't see the endpoint for the titration. If after adding iodine, the oil remains the same color, this means that the iodine is being consumed by double bonds in the fat. In this analysis, the end point is the number of drops of iodine you add before the iodine color persists or remains colored. For this analysis, you need to keep adding iodine solution until the iodine color stays in the sample. Why don't you try a small sample of a saturated fat like lard or butter and try your test again? If you were using a polyunsaturated oil like olive oil or canola oil for your test, lots of iodine would be required before you saw a color change. A fat that is solid at room temperature like butter or lard has much fewer double bonds, so you should see the end-point (iodine stays iodine-colored) more quickly.

Here is website that lists the iodine number of various oils and fats:

http://journeytoforever.org/biodiesel_yield.html

Here is website that describes atest for the iodine value. What are the differences between this protocol and your protocol?

http://www.iupac.org/publications/pac/1 ... 2x2339.pdf

I hope this helps!

Donna Hardy

Hi,

Sorry if I wasn't very clear. I thought the iodine was supposed to be purple like the experiment said it would be, but it was a yellowish brownish color instead. When I added the drops to the oil samples, it made it look yellowish brownish like the iodine, but it never turned clear. I didn't see a change. The oil never went back to looking the way it did before I added the iodine drops. So I still don't know why this isn't working, but I will try it with the butter like you suggested. Will this experiment work if the iodine isn't purple?

Hi,
It seems like some other students are also having the same issue as you with this experiment. My best piece of advice at this point would be to carry out the experiment assuming that the iodine really is purple. In other words, the yellowish brown color that your iodine tincture color will replace the purple that is given in the Science Buddies guide. So, if the oil/butter/lard turns the yellow-brown color and then back to its original color, then you have succeeded. I will let Science Buddies staff know about this issue, and I wish you the best of luck on your project!

Hi,

With this titration the solution will turn purple at the end point. The problem you are having is probably either due to the composition of the iodine solution you are using or to the fact that you have never added enough iodine to get to the endpoint. If you can go back and provide detailed questions to all of the questions I have posted, I will explain what the problem is and what to do to correct it. So far, all I know if that you haven't seen any purple.

It's perfectly OK to turn in a project that has unexpected results, but it will be helpful if you can explain the science behind your project and, in this case, explain why you didn't see a purple color. If you project is due tomorrow, you don't have time to do any more experiments, but you do need to concentrate on the write-up.

Please let me know what grade you are in, whether or not you have had chemistry yet, and whether or not you understood any of the chemistry links I posted.

Donna Hardy

Hi,

Here is some information that should help explain why you didn’t see a purple color. The problem can be explained by comparing the differences between the procedure in the Science Buddies website and the standard protocol for this analysis. I don’t know how much chemistry you have had, so please go through this explanation slowly and let me know if there’s any part that you don’t understand:

Here is a website that shows how iodine solution reacts with double bonds of unsaturated fatty acids. Please note that the reaction results in the disappearance of one iodine and one chloride per double bond.

http://www.4college.co.uk/a/Cd/Oil.php

Science buddies procedure:

The procedure recommended in the science buddies website suggests adding the tincture of iodine to the hot oil to the sample until the color of the iodine remains in solution after the solution is mixed and heated briefly. The color of the iodine is described as purple, but, as you have noted, tincture of iodine is yellowish brown. So, if you follow this procedure, you would continue adding the iodine until the color remained yellowish brown after a few minutes incubation time.

https://www.sciencebuddies.org/science- ... p062.shtml


Now, here is the composition of 7% tincture of iodine. Is this the iodine solution that you purchased?

http://www.answers.com/topic/tincture-o ... P_formulas

50% ethanol, 7 grams of iodine (I2) and 5 grams of potassium iodide (KI)


Standard method for iodine value:

Here is the standard method for measuring the iodine value. Please notice that this method is different than the method in the Science Buddies website. Please also note the composition of the iodine solution used for the standard test method.

http://ibchem.com/IB/ibfiles/organic/or ... _value.pdf

The differences between the standard method and the Science Buddies method are:

1. The sample is dissolved in carbon tetrachloride, an organic solvent (compared to no solvent in SB protocol until small amount of ethanol is added in tincture of iodine solution). The protocol requires dissolving the fatty acids in an organic solvent, and the SB protocol does not include this step. Carbon tetrachloride is carcinogenic, so I don’t recommend that you try this.
2. The iodine solution is composed of Iodine monocloride ICI in glacial acetic acid (compared to iodine and KI). However, both solutions contain iodine (I2), which should react with the double bonds in the fatty acids, so this difference should not be significant.
3. An excess of the iodine solution is added to the sample at the beginning of the analysis time (compared to adding it drop wise from the beginning). It takes time for the iodine to break the double bonds, so after the iodine is added, the sample has to be stirred and incubated for a while after every addition of the iodine solution with the SB protocol.
4. The iodine solution and sample are incubated in the dark for one hour (compared to no precautions on light exposure). Iodine is very sensitive to light, so this could cause a problem if the experiment is conducted in the presence of light.
5. The amount of iodide remaining in the sample is titrated with sodium thiosulfate solution, which oxidizes the iodide to iodine (this is not part of SB protocol).
6. The iodine solution will turn dark purple if a starch solution is added, (compared to no starch solution in SB protocol). Refer to attached protocol. This is the main reason you didn’t see a purple color.
7. The amount of sample used is determined by the anticipated iodine value (compared to using same quantity for each sample). Refer to the attached protocol. Samples that are higher in unsaturated fatty acids would require very large volumes of iodine solution with the SB protocol. That’s why I suggested that you try a sample of butter, so you could see an endpoint a little quicker.

The differences in the test methods are interesting. The Science Buddies protocol has been simplified to make it easier to do, but the changes may have caused a problem for you. If you want to see a bright purple color, try running a blank sample (no oil) and add a few drops of 3% starch solution to your sample. The solution will turn purplish as soon as there’s an excess of iodine, which should be immediately with a blank sample.

http://www.elmhurst.edu/~chm/vchembook/ ... odine.html


Please let me know if you have any questions.

Donna Hardy

Hi,

I tried the experiment with butter, but it still didn't work. I started with three drops of iodine which turned the butter yellowish orange, stirred it and waited for about 15 min., but it never returned back to its original color. (I compared it to a test tube of just butter). I think it is the iodine that's the problem. The one I used said: Iodine 7%, Potassium Iodide 5%, Alcohol 85%.

Also, my teacher extended the due date, so if I hope to find the right iodine and try it again; otherwise, I guess I'll just have to turn it in as is. Thanks for your help!

Hi,

It’s good that your teacher has extended the due date; this will help.

Thanks for giving a little more detail about what you actually did. The information is very helpful. I don’t think the problem is due to the iodine.

Before you try testing a sample again, please go back to my previous posts and read all of the information. Please post questions about any information that you don’t understand. The chemistry of this project is very interesting and you need to understand what is happening, otherwise the experiment is not going to work for you. In this experiment, you are titrating the double bonds in the fats with iodine. The iodine reacts with the fat until there are no double bonds left. The solution will remain colored as soon as all of the double bonds have been broken, leaving excess iodine in solution.

If you think you understand the information, please continue with the following:

After you added the iodine solution to your sample, the double bonds in the fat consumed the iodine and it disappeared from the solution. The iodine became covalently linked to the fatty acid, so you did not see the iodine color. If you had continued adding iodine, you would have seen the iodine color remain eventually. You need to keep adding the iodine until the solution does not turn clear. The number of drops of iodine will be proportional to the number of double bonds in the fatty acids.

To help you see the reaction better, I recommend that you make a starch solution using 1-2 tsp of cornstarch in a cup of water. Heat this while stirring on top of the stove until the starch solution becomes clear, you can add more water it it’s too thick. If you don’t have cornstarch, you can use flour, a piece of bread, or mashed potatoes to make a starch solution. But do try to use cornstarch if you can because it will be clear solution and easier to see.

Next, add a drop of iodine to the starch solution. You should see a dark blue-black color.

If this works, then try the fat titration experiment again, this time using a blank (water). With a blank, you should see the blue black color as soon as there is an excess of iodine, which should happen with just a few drops of iodine. If this works, then try the butter sample again.

If you spend the time to understand the chemistry, and if you follow my directions, I predict you will be successful. However, if it doesn’t work, then please send me a detailed description of what you did, and we’ll try again. You could stop and write up your experiment as it is, because you have done so much work, but I encourage you to try at least one more time.

Please let me know what happens.

Donna Hard

Hi,

I am following up to find out if you were able to complete a successful titration on your project with a visible endpoint? Were you able to complete your project?

Donna Hardy

I'd just like to know if anyone has the procedure and pretty much all the information for the project, because fro some reason I tried to look it up, but the link could not be found. Thank you

Hi Cygarnica - This project was recently removed from the Science Buddies Project Ideas directory because the idoine called for (7%) is now a controlled substance and listed on the United States Drug Enforcement Agency's List 1 list. Using a 2% iodine didn't have the same reliable effects for the project, so the project was removed.

If you need assistance finding another great science project to work on, please consider taking the Topic Selection Wizard survey or browsing the Project Ideas library. You can get input from our Experts here at Ask an Expert, but we would ask that you start a "new" thread so that our Experts can better assist you!

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Science Buddies