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I posed this question at the Seasoned Advice SE and thought I might get some more information here.

Traditionally prepared corn is cooked in a calcium hydroxide solution to make it more digestible, but when my search for $\ce{Ca(OH)2}$ hit a dead end, I began thinking: could I make a substitute with stuff I already have (sodium hydroxide, which I use for pretzel/soap making; and calcium chloride, for brewing)?

My thought process was that, upon dissolving, sodium hydroxide plus calcium chloride would provide the same ions (though not necessarily in the same concentration) as calcium hydroxide and sodium chloride. Since I would be adding salt to this recipe at some point anyway, I didn't see any harm to this.

Is this feasible, or am I off-base in my chemical understanding about this? More importantly, is there some chemical consideration I've failed to take into account?

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2 Answers 2

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Your idea seems mostly sound, but one thing you should consider is the solubility of calcium hydroxide (a.k.a. slaked lime). It is fairly low.

That low solubility provides you with an opportunity. If you have calcium chloride and sodium hydroxide, you can mix saturated solutions of both and a white precipitate should form. The precipitate is calcium hydroxide. You can then remove the precipitated calcium hydroxide, wash it with ice cold water, and then you'll have $\ce{Ca(OH)2}$! A YouTube demo of this idea provides some more details.

$$\ce{CaCl2(aq) + 2NaOH(aq) -> 2NaCl(aq) + Ca(OH)2(s)}$$

I think this method is preferred because the low solubility of calcium hydroxide compared to sodium hydroxide naturally limits its alkalinity and corrosiveness. It would be too easy to use undesirable (and possibly even dangerous) levels of NaOH if you made a mistake in how much you used for nixtamalification. Additionally, simply mixing NaOH and calcium chloride and using the resulting milky liquid as a substitute for calcium hydroxide will have far too much salt (NaCl) present to be a good substitute. Or conversely, if you lower the amount of NaOH and calcium chloride to where the saltiness is tolerable, you will have too little alkalinity.

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  • $\begingroup$ I see. Thanks for the advice. How complete would this reaction be? As in, if I measured precisely, would I end up with fairly close to 100% Ca(OH)<sub>2</sub> and salt water at the end? Or would there be significant amounts of calcium, hydroxide, sodium and chloride ions left in the water? $\endgroup$
    – Franklin P Combs
    Mar 31, 2015 at 15:47
  • $\begingroup$ You could calculate this if you wanted from the solubility product of calcium hydroxide. By a very rough back of the envelope calculation, if you used 1 molar calcium chloride and 2 molar of sodium hydroxide, the concentration of calcium ions left in the solution would be about 10 millimolar. That is, the reaction should be about 99% complete. $\endgroup$
    – Curt F.
    Mar 31, 2015 at 17:09
  • $\begingroup$ Am I right that calcium hydroxide's solubility decreases as temperature rises? If so could I push the reaction even farther by boiling the solution? $\endgroup$
    – Franklin P Combs
    Mar 31, 2015 at 17:29
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If the purpose is purely for experimentation, the above answer is the way to go. However if you just need calcium hydroxide, you can purchase it in a food grade form called Cal Mexicana, which is used to remove the husks from corn prior to making corn flour for tortillas with an added benefit of increasing the bioavailability of niacin in corn.

I know the question is old, but someone who just needs calcium hydroxide for say hydroponic/aquaponic pH adjustment, this is a safe and inexpensive solution.

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  • $\begingroup$ Thanks, the issue was always availability. I knew what I was looking for was pickling lime or cal or whatever, it just was not available at any stores near me and so I figured rather than order it online, I would see if I could make it with what I had on hand (so it was a bit of an experiment). $\endgroup$
    – Franklin P Combs
    Oct 22, 2017 at 21:54

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