Mixing potassium citrate and La Croix?
December 9, 2017 10:32 AM   Subscribe

For a potassium source that's not too basic, I'm adding potassium citrate to La Croix sparkling water, which I'm assuming is acidic (carbonic acid?). What is happening when it starts fizzing?

I expected this because of baking soda and vinegar, but what molecules and ions am I drinking, now, and am I going to die?

Apparently, potassium citrate is very basic which is a different kind of bad for your tooth enamel than very acidic things. So, instead of adding potassium citrate to water I decided to add it to an acid.

Why doesn't the fizzing occur when I add potassium citrate to orange juice?
posted by zeek321 to Science & Nature (7 answers total)
Oh, I figured that if all the potassium citrate dissolves and there's no fizzing, then I've got a solution that's relatively more neutral than its previous pH, though I think I'd have to do something more careful if I wanted neutral pH, right?
posted by zeek321 at 10:34 AM on December 9, 2017

I suspect the effect is merely physical, not chemical — the potassium citrate crystals provide nucleation sites for the conversion of carbonic acid to carbon dioxide (the gas released) and water. This is something that would happen anyway if you just let the La Croix sit — and this is what creates the bubbles in carbonated water on its own — it just happens a lot faster when you provide nucleation sites.

I decided to sacrifice a can of La Croix of my own to test this. I poured it into a glass, and added a tablespoon of table salt, with the prediction that if it was the presence of nucleation sites, it would fizz up. Table salt, a.k.a. sodium chloride, has no effect on pH, and should not chemically react with carbonic acid.

Reader, it fizzed.

Potassium citrate + orange juice does not fizz because there is no carbonic acid, so no potential source for carbon dioxide.

Adding potassium citrate to an acid generates citric acid, which does not decompose to provide a gas. Citric acid should not be harmful in moderate amounts; it occurs naturally in the body, plus it's present in citrus juices.

Two effects will contribute to the increase of pH when adding potassium citrate to carbonated water: the decomposition of carbonic acid with the release of carbon dioxide, and the addition of the base (potassium citrate) itself.

You are correct that you cannot know that your mixture is neutral (pH 7) just because it has stopped fizzing. If you overshoot the necessary amount of potassium citrate, the solution becomes basic. You'd need some way to measure or test the pH of the solution.
posted by DevilsAdvocate at 10:56 AM on December 9, 2017 [7 favorites]

I think the fizzing is due to the potassium citrate crystals being a nucleation site for CO2. Same idea as dropping ice into a soda. If there is an actual acid-base reaction happening, you'd end up with a salt + water. In that situation, if you want a pH of 7, you have to know the starting pH's of the potassium citrate and the LaCroix, as well as balance the number of moles of each. You'd also need some sort of pH indicator which would change color when you hit a neutral pH. I do not recommend drinking most pH indicators.
posted by basalganglia at 10:58 AM on December 9, 2017 [2 favorites]

Red cabbage juice is a natural pH indicator which would be safe to drink, if you were inclined to do so, although I can't say what it would do to the flavor of your drink. But it's not like you have to mix whatever pH indicator you choose with the entire glass; you can remove small samples from the glass and test those as you go.
posted by DevilsAdvocate at 11:15 AM on December 9, 2017

Huh, if all the carbon dioxide evaporates(?) due to nucleation then I'm basically drinking a very basic, La Croix flavored solution again?
posted by zeek321 at 11:15 AM on December 9, 2017

That's a surprisingly complex question, as it involves carbonate/bicarbonate/carbonic acid/carbon dioxide and citrate/monohydrogen citrate/dihydrogen citrate/citric acid equilibria.

Near as I can figure with some back-of-the-envelope calculations after looking up the relevant equilibrium constants, once it's flat it might be very basic or slightly basic or neutral or possibly still very slightly acidic (but so slightly acidic, ~pH 6, that it could be considered neutral for practical purposes).
posted by DevilsAdvocate at 11:31 AM on December 9, 2017

(I was a chemist in the 90s, now I use chemistry experience mostly for data analytics, and for mixology, which is a hobby of mine.)
The pH of Potassium Citrate is in water is generally 8.5, which puts it in the realm of a weak base. The chemistry, thermodynamics, and kinetics of CO2 is pretty complex, and changes with temperature (the lower the temperature, paradoxically, the better the absorption of it by H2O, under pressure). The pH of CO2 in water is usually around 3.5 - 4, which makes it a weak acid.

Normally with strong acid/base reactions (depending on the acid and the base involved) there can be gas-releasing neutralization reactions. But gas-release here is (I think) far more likely the result of nucleation than of release from acid/base reaction (because both the acid and the base in this system are weak). Adding potassium citrate (the base) to aqueous CO2 would yield, if the acid-base structure were kinetically and thermodynamically more favorable than the nucleation reaction, various potassium/hydrogen forms of citrate, where one or more of the 3 potassium ions were replaced by tacit bonds with hydrogen instead, water, and possibly a gas/liquid byproduct. (The citrate neutralization reaction is a reasonably well known biological buffer solution/system, which you'd have to look up on your own if you wanted more info.)

Personally, I wouldn't test nucleation with table salt. Primarily because table salt is highly soluble in H2O, so you're sort of having salt solubility battling against physical nucleation sites. Instead I would test by adding, perhaps, sugar, which isn't as soluble in (especially cold) H2. Or something even less soluble like find sand or some other powder that is physically similar to the potassium citrate.

Also it's notable that in brewing and carbonation circles/industries, the measure of carbonation is not acid/base/pH, but measured by the "volumes" of (normal pressure) CO2 that is dissolved in the fluid (almost always H2O (while being agitated under a great deal of pressure from pressurized CO2.
posted by kalessin at 3:02 PM on December 9, 2017 [2 favorites]

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