# How to dissolve chalk (CaCO3)?

I've read that vinegar can dissolve $$\ce{CaCO3}$$, I know that extreme heat can decompose it, but how to dissolve $$\ce{CaCO3}$$ at home? I need to dissolve chalk in my home because of repairing something. Can someone help me do it without heating $$\ce{CaCO3}$$? Any replacement for that?

• As you noted, how about vinegar? That is a fairly common household item. – Jon Custer Mar 14 '17 at 12:52
• as I know the reaction process (CaCO3 + Vinegar) is very slow, do you know another thing which can make the reaction faster? Can heating Vinegar help speed up the reaction? As I know heating can affect reactions, but I'm not sure about this reaction... – Amir F Mar 14 '17 at 12:57
• If you want to repair something with $\ce{CaCO3}$, than it sounds like using glazing putty; especially near to wood. Vinegar however is an acid that will start to decompose the carbonate in chalk, yielding CO2. Instead I recommend either a mixture of (finely ground $\ce{CaCO3}$ and water) -- like a paste, or lineseed oil. – Buttonwood Mar 14 '17 at 13:23
• There are products on the market for defurring the inside of kettles, you need one of these. They mostly contain sulfamic acid – Waylander Mar 14 '17 at 13:28
• Chalk is not noted for being particularly strong - scrape the bulk of it off and finish with some vinegar on a sponge or cloth. – Jon Custer Mar 14 '17 at 13:36

$$\ce{CaCO3}$$ is sedimenting when mixed with water, and therefore is not easy to remove with hot water. Nevertheless several methods exist that actually dissolve it that are better than vinegar:

• You could add hydrochloric acid again to convert it into soluble Calcium chloride, according to equilibrium: $$\ce{CaCO3 (s) + 2 HCl (aq) <=> CaCl2 (aq) + H2CO3(aq)}$$
• You could use carbonic acid instead $$\ce{CaCO3 (s) + H2CO3 <=> Ca(HCO3)2}$$ this is the reason shells are getting dissolved by an increase of the amount of carbon dioxyde in solution: $$\ce{CaCO3 (s) + CO2 (aq) + H2O <=> Ca(HCO3)2}$$
• But I recommend Sulfamic acid ($$\ce{H3NSO3}$$), is frequently used for removing rust and limescale, replacing the more volatile and irritating hydrochloric acid, it may be a little more expensive but is certainly not toxic.
• Sulfamic acid is an eye irritant, however. – James Gaidis Mar 29 at 14:07
• Lots of things are eye irritants, including orange oil, so we have to live with that with any chemical method. – Oscar Lanzi Apr 26 at 16:40

Calcium carbonate will dissolve quickly in a strong acid, like hydrochloric, even if it is dilute and therefore not so dangerous.

An organic acid has a problem in that it may have a relatively low pH at first, but after it dissolves a bit of the $$\ce{CaCO3}$$, a significant amount of the acid anion is formed in the solution, which stifles the ionization of the acid, so the rate of dissolution slows down. So, vinegar is OK, but you need to use a lot.

Perhaps the problem is with the other materials, which may be binders (as Buttonwood suggested). Perhaps an organic solvent could dissolve the binder and thus remove the chalk.

However, it may be that the "chalk" is not $$\ce{CaCO3}$$, but rather a prepared mixture with clay or gypsum (https://en.wikipedia.org/wiki/Chalk). In that case, trying to dissolve traces remaining from your project will not be easy. Try to dissolve some of your "chalk" starting material - if it can't be dissolved easily, you may be directed toward mechanical methods.

Basically $\ce{CaCO3}$ is not soluble in water but it can disperse in water by using a dispersing agent. The solution looks like milk . The viscosity of solution up to solid content or quantity of $\ce{CaCO3}$ in solution. That is my opinion.