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Old Dec 19th 2017, 08:02 AM   #1
Karsty
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Acid + ????? = bubbles

Hi there,

Just joined, not a chemistry expert but have a pretty good basic knowledge of it.

I have a bit of a mystery......

Now, I was taught that acid + carbonate = salt + water + carbon dioxide. Nothing strange there, right?

So, I bought some sand, of natural origins, which on the whole appears to be quartzite, which is inert to acid, right? It is guaranteed lime-free, but I just happened to mix a bit of it with dilute sulphuric acid, and it started bubbling quite energetically.

Is there anything else that could be causing this other than calcium(or magnesium) carbonate?

Many thanks for any help here. This sand is from a very reputable source and I want to make sure it is not contaminated.

Sorry if I've posted this in the wrong forum, I don't actually know how deep this chemistry might go, I only assume as far as I know.

Karsty.

Last edited by Karsty; Dec 19th 2017 at 12:18 PM.
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Old Dec 19th 2017, 07:31 PM   #2
oz93666
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Your sand may well be lime free... lime will not produce bubbles with acid , just water and calcium sulfate

I think it's most likely the sand has some particles which come from the shells of sea creatures crabs etc ... calk or limestone could also be in the sand , these too were originally the shells of sea creatures ...all are calcium carbonate .. just a tiny amount of this will produce a lot of bubbles . for most uses this carbonate is not a problem ..

If it's essential not to have this , then treat with dilute acid till no more bubbles , I can't imagine there's much carbonate in there ... collecting the gas will confirm it is CO2 when it extinguishes a flame ...

Extremely unlikely, but there could be metal particles in the sand , produce H2 with acid
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Old Dec 20th 2017, 12:08 AM   #3
Karsty
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Thank you oz93666

In terms of horticulture, lime also includes calcium carbonate, and also includes dolomitic lime at a push. It's pretty much a catch-all term for alkaline calcium compounds.

The point is that it is guaranteed to be free of these compounds, and that's a big deal for a horticulturalist. "lime"-free must mean alkaline-calcium(or magnesium)-compound-free.

I'm actually waiting for analysis results back from the company to let me know what's going on here. They are initially saying they are satisfied the sand is good, but I await chemical information. I will check to see if the gas extinguishes a flame.

I actually bought 2 different types of sharp sand from B & Q, one, labelled Diall, looked great, only cost 2.30 for a 25L bag, and produced almost completely no bubbles. The other type under the label Tarmac wasn't quite as good and produced more bubbles, but still less than the official horticultural make, which incidentally goes for about 7 for 25L! So you can see why us plant growers are concerned.

Thanks again,

Karsty.
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Old Dec 20th 2017, 12:59 AM   #4
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I see ..I guess you're worried about Ph, the calcium ions won't cause problems.. (you can also use vinegar for the bubble test instead of sulfuric acid )

I suspect you're worrying too much ... I've used many different media for hydroponic growing .. including pea gravel and sand , always bought it from the building supply company , never had problems ... good luck ...oz
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Old Dec 20th 2017, 07:40 AM   #5
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Hi Oz,

Well, easily said. However, there are many many plants in the plant Kingdom that are badly affected by high pH with calcium ions present. Take for example the Ericaceae. There are exceptions, but generally, if too high a pH is caused by many calcium ions, it prevents them from taking up iron and/or magnesium and/or manganese, resulting in different variations of chlorosis. That's why we worry about it

Last edited by Karsty; Dec 20th 2017 at 09:35 AM.
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Old Dec 20th 2017, 08:10 PM   #6
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Hmm ...I don't know , my experience , and gut tell me that calcium carbonate is so mildly alkaline , in shell form almost insoluble , and will be present in such very small amounts in sand , that this , realistically is not an issue ... Where ever any sand comes it will have had water moving through it , from rain , sea , and this will remove all soluble elements ... when you add acid the bubbles come from insoluble grains , like sea shells , and insoluble grains shouldn't cause you problems.

I suspect it's a myth pushed by horticultural companies to charge ridiculous prices for sand ... when in 99% of cases building sand is fine ... if living near the sea I would get sand from the shore ...and wash it to remove traces of salt.
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Old Dec 21st 2017, 08:13 AM   #7
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The thing is, gardening is not a strict scientific discipline, and the shells contain calcium carbonate, whether soluble or not. In gardening terms it's still under the heading of lime, and if the sand is guaranteed lime-free, there should not be any calcium carbonate in it in any form. Moss peat has a pH of about 4, I'm sure it would dissolve in that.
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