Science Buddies: "Ask an Expert"

Dear Science Buddy Expert

I have chosen one of your science experiments for my school science fair, it's called Determining Iodide Content of Salt.

I have tested five different types of salt but unfortunately none of them have changed to the colour purple not even the iodised salt. As you can imagine I'm worried about handing in a failed science project. I have discovered after reading through the "Materials and Equipment" area of the science buddy experiment, there is a paragraph which advises some nations use potassium iodate (KIO3) as an iodine supplement in iodized salt which will not work in this experiment. I live in New Zealand and after checking the iodized salt container I used, they do use potassium iodate. This experiment using hydrogen peroxide, vinegar and starch will not detect iodine added as potassium iodate.

Can you suggest any alternative chemicals I could use that would detect potassium iodate? Any other suggestions on how I can save my experiment would be greatly appreciated.

I have emailed the Cerebos Salt company here in New Zealand and they have kindly sent me a letter confirming they do add potassium iodate to their salt. Hopefully this will give some credibility to my project.

I look forward to your earliest reply, my project is due on Monday 17th November.

Thank you very much for your time.


Kind Regards
Sarah Ellis

Hi Sarah,

First, I want you to know that your science fair project has definitely not failed. You may not have gotten the result you were wanting (or expecting), but the outcome of your project is perfectly valid information. You followed the scientific method, which is what doing a science fair project is all about. As a professional scientist, my experiments don't always turn out the way I expect them to. When that happens, I learn something new by analyzing why the experiment didn't turn out the way I thought it would. Data--even unexpected data--is important information. It sounds like this is exactly what happened with your experiments. You, too, learned something new--you learned that the iodine in the salt you tested was added as potassium iodate. (I suspect you didn't know that before you started the project!) I really admire the way you have thought about why your experiments turned out the way they did. It shows a great deal of scientific maturity.

Here's how I would handle presenting your project. You can present your question, hypothesis, materials, procedure, data, and results exactly the way they are. In your conclusion section, you should state whether your hypothesis was correct. Then--this is the important part--explain why your experiment turned out the way it did. You might say something like, "Surprisingly, I did not detect iodine in the iodized salt I tested. I did some research and found out that in New Zealand, potassium iodate is added to the salt. My test doesn't detect that iodine compound. This is why my experiment turned out the way it did."