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  • Earth.

  • Billions of years ago, it was just a hot jumble of elements,

  • which over time have solidified into the very rocks

  • that we stand on.

  • Right?

  • OK.

  • These rocks have come from a quarry in Portland, and

  • they're made of limestone, which is a

  • type of calcium carbonate.

  • Masons would use these blocks pretty much as they are in the

  • construction industry.

  • These rocks have been formed over millions of years from

  • shells like this.

  • So these have just collected at the bottom of the ocean and

  • been compressed, and we can actually even see some of the

  • shells in this rock here.

  • Because the shell and the rock are made of the same chemical

  • substance, calcium carbonate, they have the same chemical

  • properties.

  • So here we have some hydrochloric acid.

  • And the bubbles that you see instantly formed in here, this

  • is carbon dioxide gas.

  • There's another way we can drive out the carbon dioxide,

  • and that's simply by heating it.

  • So this block now has been in the oven for 24 hours.

  • It was allowed to cool overnight.

  • And well it looks pretty much just the same as it did

  • before, but actually, it's completely different.

  • its chemical structure has now changed.

  • Before, we hand calcium carbonate, and heating it up

  • drives out the carbon dioxide and leaves us with calcium

  • oxide, or quicklime.

  • Because we've driven out all of the carbon dioxide from

  • this rock, it's actually lost quite a lot of its weight.

  • But it's also changed in structure, and we're now going

  • to see why it is that you won't find any buildings made

  • out of calcium oxide.

  • The change that takes place when limestone is converted

  • into quicklime, or calcium oxide, has been known for many

  • hundreds of years.

  • Here, in this book from 1526, we see the process.

  • We see a chap with a furnace in the background and boulders

  • of limestone and he's pouring water on this.

  • Quicklime literally means, living lime.

  • And we can see this as the water instantly vaporises.

  • It's turning into steam in this very violent reaction.

  • It's combining with the quicklime, we can see it

  • crumbling away, blistering.

  • Bits of it are flying off, popping in all directions,

  • generating a lot of heat, which we can see

  • as the steam here.

  • During this process, called slaking, the calcium oxide

  • reacts with the water to form calcium hydroxide, and this is

  • a key component of cement.

  • This has been used since Roman times and

  • it's still used today.

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B2 中高級

碳酸鈣 - 崩解速凝劑 (Calcium Carbonate - Disintegrating Quicklime)

  • 367 24
    Bing-Je 發佈於 2021 年 01 月 14 日
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