Sciencemadness Discussion Board - Calcium carbonate solution

Calcium carbonate solution

bolbol - 4-7-2016 at 17:51

I would like to know whether or not a perfectly saturated solution of calcium carbonate would react with the water to form calcium hydroxide if left for over a month?

blogfast25 - 4-7-2016 at 18:15

CaCO₃ is of course very poorly soluble. Due to hydrolysis of the carbonate ion, such a solution contains also hydroxide ions in low concentration.

This doesn't take much time to achieve, in fact it's almost instantaneous. But a solution of Ca(OH)₂ this does not make.

Some more information, here:

http://www.sciencemadness.org/talk/viewthread.php?tid=65303#...

bolbol - 4-7-2016 at 19:37

Is there anyway I can precipitate out calcium carbonate and also magnesium carbonate from a solution? What sort of solution would I need?

j_sum1 - 4-7-2016 at 22:07

Quote: Originally posted by bolbol

Is there anyway I can precipitate out calcium carbonate and also magnesium carbonate from a solution? What sort of solution would I need?

Not 100% sure what your question is but...

If you begin with a soluble calcium salt or magnesium salt in solution, (CaCl2, MgCl2 springs to mind) and then add a solution of a soluble carbonate (KCO3 or NaCO3) then you will indeed get a precipitate of CaCO3 or MgCO3.

This is the classic double substitution reaction. It is one of the most useful ways of separating ionic species.

Be warned, the carbonates formed will be extremely fine and will clog up any filtering equipment you care to use. Mest to let it settle for however long it takes (perhaps days) and then decant the clear liquid off the top.

bolbol - 4-7-2016 at 22:44

No I don't want this to involve any chemical reactions. I just want to take a solution of those carbonates and precipitate them out onto something else by using evaporation.

j_sum1 - 4-7-2016 at 23:43

Well, yes. If you evaporate the water you will be left with your carbonates. They will appear as a thin white dusty film on the surface of your container.
That should not be surprising.

Let me reiterate that MgCO3 and CaCO3 are really quite insoluble -- 0.00106 g/L and 0.013 g/L respectively at 25°C. (Wikipedia)
Making a solution will be painful. And when you recover the material you won't get much.

What is it that you are really trying to do?

bolbol - 5-7-2016 at 07:33

But if the carbonates react with the water won't I be left with the hydroxides of calcium and magnesium at the end?

I am trying to deposit it onto different kinds of calcite which is calcium carbonate itself and observe any differences with different ratios and quantities of the carbonates involved and maybe some other things depending on how it all turns out

bolbol - 5-7-2016 at 07:37

But if the carbonates react with the water won't I be left with the hydroxides of calcium and magnesium at the end?

I am trying to deposit it onto different kinds of calcite which is calcium carbonate itself and observe any differences with different ratios and quantities of the carbonates involved and maybe some other things depending on how it all turns out.

Edit: The calcium carbonate solubility you wrote is per every 100 mLs. At room temperature 12-15 mgs should dissolve in a liter

blogfast25 - 5-7-2016 at 08:44

Quote: Originally posted by bolbol

But if the carbonates react with the water won't I be left with the hydroxides of calcium and magnesium at the end?

I am trying to deposit it onto different kinds of calcite which is calcium carbonate itself and observe any differences with different ratios and quantities of the carbonates involved and maybe some other things depending on how it all turns out.

No. Just like when you crystallise a soluble carbonate (like Na₂CO₃), CaCO₃ will crystallise out.

bolbol - 5-7-2016 at 09:44

I have heard that the carbonate reacts with the partialy ionized water to make carbon dioxide and calcium hydroxide. For my application it's important that nothing is in the water besides the calcium/magnesium carbonate.

Boffis - 5-7-2016 at 11:00

When water comes in contact with calcite (natural calcium carbonate) the pH rises due to the equilibrium:

2CaCO3 + 2H2O → Ca(HCO3

2 + Ca(OH)2

The later substance makes the solution alkaline. However, the equilibrium lies a long way to the left and the concentration of the components on the right is very low, this is merely a hydrolysis reaction. This reaction will not progress further and the resulting solution will absorb CO2, if give the oppurtunity, pushing it further to the right by mopping up the hydroxide ions; there is no way you are going to get CO2 evolved. Calcium bicarbonate is produced and it is much more soluble then calcium carbonate which is why hard water can contain 200mg/l of calcium or more.

Artemus Gordon - 11-7-2016 at 15:04

If you are looking for a source of CaOH, find a Mexican supermarket if you can. In the spice section they sell a pure white powder called 'cal'. This is food grade CaOH that is used to turn dry corn kernels into hominy.

halogen - 11-7-2016 at 19:34

I believe it's a geological experiment.

Ozone - 11-7-2016 at 20:28

Even if you were to get hydroxide (which as you now know is strongly disfavored), it will scrounge CO2 from the air to give you the carbonate. For example, a 50% w/w solution of NaOH stirred in air will develop insoluble (in 50% NaOH) sodium carbonate quite quickly (a huge pain in the ass if you are doing ion chromatography--this is why we prefer to keep NaOH eluents under He or to use an electrochemical eluent generator). Lime water, even faster (apparently) due to the extreme insolubility of the calcium carbonate.

I suppose one could deposit a calcium hydroxide layer (from milk of lime) under CO2.

O3