Photo: Jurii CC-BY-SA

by Simon Jones

Iodine is a chemical of many properties and uses, and that’s what I want to explore in today’s chemistry week blog as well as some of its history and some nice resources making use of the latest of the halogens to be explored in our chemistry week blogposts.

Iodine was discovered in 1811 by French chemist Bernard Courtois.  It is named after the Greek word ‘Iodes’, which means violet, because Iodine produces a gas which is a very strong purple colour. It was, like so many accounts of chemical history, and accidental discovery. The original discovery was made when Courtois was extracting sodium and potassium from seaweed, in order to make gunpower in the desperate times of the Napoleonic war. However, in using too much sulphuric acid to clean the compounds, Courtois created a cloud of purple gas.

Good job they made all this into gunpowder before D-Day. Photo: Helen Wilkinson CC-BY-SA

And what has Iodine ever done for us? First and foremost, we need it in our diet. A lack of Iodine directly affects the thyroid gland. Moreover through trial and error, Iodine was discovered as a cure for thyroid disease. It is argued this is the first case in medicinal history of a specific disorder being treated by a specific cure. Iodine was found to be so important in our diet, that it’s now become part and parcel of everyday foodstuffs; in particular it is found in table salt. And so we’re now all kept healthy and free from thyroid disease; except people who have a thyroid deficiency (hypothyroidism) and need hormone replacement to keep the thyroid gland active.

That’s one use of Iodine, however I’d like to touch upon another (if you’ll pardon the pun). We can mix Iodine with the poisonous and pungent Ammonia to create a horribly sensitive explosive; Nitrogen Triiodide. This substance is so volatile even the force of being tickled by a feather will set it off!  The fact that this explosive is touch sensitive and is primed when dried out (taking varying amounts of time depending on the conditions) means that it’s actually not very reliable and so not generally used.  It is impressive though

And finally, it’s worth thinking about Iodine as a useful element in purifying water and making it drinkable. Iodine is anti-microbial, meaning it renders a lot of the bacteria found in fresh water inert. However, it’s not a perfect disinfectant. Often people living in areas without water treatment, or travellers adventuring to such places, use iodine tablets to make the water drinkable – not because it’s the most effective way, but because it is effective enough when weighing up the cost and convenience of buying and carrying tablets.

So from our everyday salt to our not-quite-so everyday explosives, and well as our ink cartridges and catalytic converters, Iodine plays a role in our lives, even if we don’t know it.

Don’t forget our ongoing RSC global chemistry experiment! We’ve been testing out our fruit for its Vitamin C content and adding the results to the data mound. Find out more, and join in yourself! Today’s a great day to try it out as it involves the element du jour- iodine!


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