I tried the iodine test with cooking oils and the iodine just stayed at the top of the oil in the test tube. It was supposed to disappear. any ideas on what i'm doing wrong?
This experiment can be used to identify the difference between saturated and unsaturated fats. If a fat (or oil) is unsaturated, it has double bonds and iodine can react with the oil and become a substituent group on the fat. If this happens, the distinctive color of the iodine will go away. You will likely have to shake the test tube to get them to mix some to see if the reaction will occur. A saturated fat will not have any reaction and the iodine will just separate from the oil.
Are you sure it was supposed to disappear? I think this experiment is a test of the density of iodine versus the density of cooking oil. Say, if the cooking oil was more dense than the iodine, the iodine would stay on top as it cannot make its way through the oil compound.
But you need to clarify what cooking oil you're using, and if you've been given any guidelines to how dense the substance is.