Science Buddies: "Ask an Expert"

My son is testing whether an oil is saturated or not using iodine. The protocols we followed worked great except the results turned out completely opposite of what we expected based on what we learned about unsaturated fats. So we expected the animal fats (butter and fish) to not turn clear and to stay brown. The "vegetable" oils, such as canola, corn, olive, would turn clear as the iodine bonds with the unsaturated fatty acids. So we had the exact opposite results and I cannot figure out why. Thoughts? Suggestions? We ran the tests three times and came up with the same results each time. Trying to help him discuss the results and I am at a loss.

Thanks for the help.

Hello,

The results of your experience could be explained by the way the iodine atoms add to carbon-carbon double bonds. For your vegetable oils, did your vegetable oils turn brown or stay the same? For example, olive oil is saturated fat, with extra virgin olive oil being about 13.8 percent of saturated fat in every 100 grams. Sometimes vegetable oils have more saturated fats so once iodine is added, they will most probably stay the same since there would be no available bonds for the iodine atoms to add onto. Vegetable oil is hydrogenated, meaning that an atom of hydrogen is added to each atom of carbon, which is bound to double bonds, so iodine would attach to this and make it clear.

What type of animal fat did you use? Meat products contain both saturated and unsaturated fats, so maybe there was not enough iodine added in, or the content of the unsaturated fat is higher than the saturated fat. A mechanical process can change double-bonded oils to single ones, which would be as in animal fat. For example, fish fat contains unsaturated fat, so the iodine would turn the oil clear if it was added. To make sure your experiment is accurate, you could use an animal fat such as butter if you haven't already, and a neutral oil such as plain vegetable oil. I have attached a link to this post that explains how iodine affects saturated vs unsaturated fats.

I hope this helps!

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

Hello aberlin!

According to the Royal Society of Chemistry, scientists use iodine to determine which types of fats are present. Iodine has a dark color which disappears when it reacts. For some chemical background: iodine atoms add to the carbon to carbon bonds in a fatty acid chain, so the color disappears when the atoms are added into a bond.

However, because of the way that iodine reacts with fats (adding itself into carbon to carbon bonds), it makes sense for the saturated fats in your experiment such as butter to turn brown and not react with the iodine because saturated fats are made up of many single bonds, which are the strongest type of bond. The reason for this is that there is no room for an atom, such as an iodine atom, to integrate itself between carbon atoms; however, in a double or triple bond like the ones present in unsaturated fats, it is much easier for atoms to come between the bonds.

So, when considering the types of bonds in the fats you used, because single bonds (saturated fats) do not allow atoms to come between them, the iodine would not lose its color when added to saturated fats because it cannot integrate itself into a bond and lose its color, so the saturated fats will turn brown.

As for unsaturated fats, the iodine will be able to integrate itself into the weaker double or triple bonds, therefore losing its color making the unsaturated fats turn clear.

However, the iodine does break into the double bonds in unsaturated fats, making them into single-bonded saturated fats. So, you may want to evaluate or change the amount of iodine you are using, as it could be turning your unsaturated fats into saturated fats; therefore causing your unsaturated mixtures to turn the dark color of the iodine.

Re-running your trials using a different technique may be best, and re-evaluating the volume of the oil and iodine you are using would also be helpful. So, check out another way to perform the experiment:

https://www.education.com/science-fair/ ... d-testing/

Another way to test whether a lipid is saturated or not that is quite easy is a heating test. When heated, saturated fats pull together and become solid because they have more atoms to pull together, while unsaturated fats do not have these extra atoms and will remain liquid, or become gases since the fat will react with oxygen in the air since it does not have enough atoms to become a solid.

I hope this helps and please let me know if you have any other questions!
-cnoonan180