• Question: if a sponge is on water it will absorb it, so why does mercury not?

    Asked by TheToppler 283 to Angus, Catherine, Jenni, Melissa, Waqar on 16 Jun 2016.
    • Photo: Angus Cook

      Angus Cook answered on 16 Jun 2016:

      Mercury is an interesting element, because (as I’m sure you know) it’s the only metallic element that’s liquid at room temperature (the other that’s a liquid is bromine, but it’s not a metal).

      I had to look up an answer to this, and it’s apparently down to a process called ‘capillary action’. A capillary is like a very very thin straw. If you put this straw in water, the water will climb up the inside of the capillary, above the surface of the rest of the water. This is without anything on top of the capillary, or anyone sucking on the end. It’s all to do with the interaction of the water with the inside of the capillary, the water finds it easy to climb up the inside surface.

      The holes in the sponge act a little bit like a load of capillaries, so the water has an easy time getting into the sponge.

      Mercury, on the other hand, doesn’t really interact with the sponge material in the same way water does. It doesn’t easily travel into the capillaries, and so doesn’t travel into the sponge.

      I saw someone suggest that you could use a metal sponge to try and soak up mercury instead, I’d be interested to see if that worked better.

      I was actually researching mercury the other day. I’m not quite sure that I understand how it conducts electricity. Just to show that we’re all still learning as we go 🙂

    • Photo: Melissa Ladyman

      Melissa Ladyman answered on 16 Jun 2016:

      Angus’ answer is great. I just wanted to add that we used to have mercury thermometers in the lab and when we got rid of them we noticed some had broken and mercury had spilled. We used a special type of sponge coated with a layer of zinc to collect the spilled mercury. The zinc and mercury combine, and trap the mercury on the sponge. I think a sponge is used because it has a large surface area because of all the holes so it can pick up as much mercury as possible.

      It’s not really the sponge picking up the mercury, but it helps! – We had to make sure the sponge was specially treated by the waste disposal company so that it wouldn’t get into the environment.

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