Magic in the classroom: The Iodine Clock

As well as being a science geek, I’m a magic geek. I’m not sure if anyone’s done the research on this, but I suspect those are two groups of people where there’s a significant overlap. I’ve got an entire live science show I do based around my love of magic and my somewhat lame attempts to become a magician and I include this demonstration as a highlight in the show. Like many of the demonstrations we’ve filmed, I don’t think video can do justice to how amazing it is to see in real life – it appears to be genuinely magical and always gets an “ooh” from the audience.

I’ve used the iodine clock in class purely for the effect it has of enthralling my students, but, as I hope the video shows, it can be used to achieve particular learning objectives. Mind you, I hope it’s clear that we at sciencedemo.org think “enthusing students” can be a sufficient justification for using a particular demo, if you’re going to take that enthusiasm and use it to help students get more out of your science lessons in general.


Get Set Demonstrate logoThis film was produced for the Get Set Demonstrate project. Click through for teaching notes, and take the pledge to perform a demonstration to your students on Demo Day, 20th March 2014.

11 thoughts on “Magic in the classroom: The Iodine Clock”

  1. Well walked, Alom. The tricky cognitive (understanding)/ affective (feelings) tightrope can be very precarious to navigate in public. We all come to it with a lot of baggage (myself included).

    The trouble is that the tightrope is entirely fabricated – many people come to a demo with a polarised worldview that we’re either “trying to help pupils learn” (code: worthy educators) *or* “we’re enthusing them” (code: blowing-stuff-up merchants).

    The fundamental point is that cognitive and affective outcomes are both important in learning, and far from being mutually exclusive are in fact significantly linked (as you say). It’s all about the demonstrator having a clear idea about what his/her particular purpose is with each demo.

    I wish we could stop judging demo presentations on our own perceptions of why *we* might do that demo in our context. There are many legitimate purposes for doing demos. Vive la difference!

    Enjoyed the video also. It *is* a truly magical demo.

  2. This is a truly lovely demo that has been around for well over a century – it was discovered by Landolt and it continues to delight, amuse, and intrigue. An old friend, my predecessor here at UCL, Glyn Williams (now at Astex Pharmaceuticals) used to do it at the start of a lecture – it would fail to do anything and he would then go on to other stuff with an embarrassed shrug of the shoulders. At the very end of the lecture, some 45-50 minutes later he would come back to it, give it a stir, and the thing would turn blue. It was a pretty devastating piece of showmanship.
    One small point. Starch does not detect iodine. It only turns blue in the presence of iodide. Iodide reacts with iodine to generate I3- and then especially I5- and it is the I5-that tangles in starch to give the charge transfer complex that looks blue. It was beautiful detective work by Tobin Marks and coworkers at Northwestern that unveiled this back in 1980 using a combination of Raman and Mössbauer spectroscopy; see JAmChemSoc 1980, 102, 3322.

  3. QUOTE
    I’ve used the iodine clock in class purely for the effect it has of enthralling my students, but, as I hope the video shows, it can be used to achieve particular learning objectives. Mind you, I hope it’s clear that we at sciencedemo.org think “enthusing students” can be a sufficient justification for using a particular demo, if you’re going to take that enthusiasm and use it to help students get more out of your science lessons in general.
    UNQUOTE
    I totally agree with this, Alom. I have also found it to be hugely controversial and one of the most widely misunderstood principles of science communication. Outspoken critics of informal science communication (such as Richard Dawkins!) never seem to understand that ‘learning’ INCLUDES the affective, emotional dimension as well as the cognitive. And as Paul McCrory has hinted, the two are inseparable.
    Here’s an example of a highly influential opinion-former getting this wrong (the ‘Exploding Custard’ scornfully dissed by Richard Dawkins in this clip is my own 23-years-old science show, by the way):
    http://youtu.be/MNEnZq9UB8U

    1. I sympathise with Dawkin’s rejection of the ‘fun’ principle. Nothing I do is explicitly about ‘fun’ and everything has a purpose within the context of a presentation. But afterwards people report that it ‘was fun’.

      But on the other hand” “Exploding Custard”: What is there not to like about that!?

  4. Alom: An even more beautiful video than the usual.
    Jonathan: The care really shows: I could see no sign of the fly at all.

    Do I remember correctly that it is possible to get this to oscillate – i.e. change back to clear, and then turn blue again?

  5. There’s absolutely no sign of the fly because the shot in which I painfully rotoscoped the bastard out ended up on the cutting room floor. From a different film.

    And no, before you ask, I’m not at all sore about that.

    Nope. Not a bit.

    Ahem.

  6. These are excellent professionally finished videos at the right length (Tom and Jerry length) and the presenter has the guts to face the camera. With my amateur videos on the CLEAPSS You tube (http://www.youtube.com/user/CLEAPSS), I do not have the time to be that slick so I keep myself out of shot. I am too busy answering questions from teachers and technicians who see a video on the web and want to replicate it. Often these videos make no comments on the safety and often not on the science as well. So I that is a real plus for you. I was involved in 3 Teachers TV programmes and I really admired the presenters in each case. I also once appeared in Man Lab and even though I have acting experience, you see at first hand just how professional James May is in the presentation.
    There have been several incidents with demos concerning, using mains electricity, igniting methane bubbles, doing howling JBs, initiating the Magnesium/silver nitrate flash, and adding sodium to water which have caused serious injury and there is all hell to pay afterwards. Nearly all the incidents which go to the HSE are from demonstrations going wrong (No! they do not go wrong, they are performed incorrectly and it is always the performer to blame; they are under rehearsed or do no seek advice from CLEAPSS or SSERC). These are caused by all sorts of teachers but there are 3 main classes
    1. The “expert” who has been doing this for 30 years and becomes blasé.
    2. The young teacher who is out to be a “whacky” “Blue Peter” style presenter (beware the multi-coloured lab coat and crazy safety specs) usually trying to get street cred with the “kids”.
    3. A teacher/technician teaching out of their specialism.
    I and my colleagues at CLEAPSS groan when a Helpline comes though to say can we do so and so for open evening, an end of term show or take this experiment to a primary school. I just know things can go wrong under those conditions.

    Bob Worley

  7. I think this article contains huge valuable information . This article can help by preventing risk and practice magic of science. Truly its a nice job. Thank you for sharing with us. All magics are science. Thanks

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