Vinegar + water + hard water deposits = magic?

August 8, 2021 5:21 PM

I put vinegar, water, and a small amount of liquid dishwashing detergent into a glass jar that had significant hard water buildup on it. The next day, the resulting solution looks odd and I can't figure out what the explanation is, or even what a plausible explanation could be.

The liquid is sort of hazy / milky, but never homogenizes no matter how much or how often it gets stirred: there are always clearer areas, with cloudier patches that appear to have small white flecks (crystals of something?) swirling around in them. But if the cloudiness was due to a suspension of tiny crystals, they'd either eventually settle out, or stirring them enough would distribute them evenly such that the liquid would appear uniformly cloudy. And yet it didn't settle after sitting overnight, and all kinds of intense stirring hasn't resulted in uniform cloudiness. Instead it always has sort of a visible "grain" to it, the way some kinds of opaque hand soap or opaque shampoos can look pearlescent when first poured (though in this case the water remains translucent).

The liquid in the jar started out about 50/50 water/vinegar by volume. The mineral buildup on the sides was hard-water buildup from tap water, which I'm guessing was mainly calcium and magnesium carbonates.

So what's going on here? I can upload a photo if needed, though I'm kind of hoping not to need to because circumstances make it kind of a pain to do.

posted by Spathe Cadet to Science & Nature (4 answers total)

I think you may have formed a magnesium silicate hydrate (MSH) gel, and/or a calcium silicate (CSH) gel.

From the MSH link:

Transmission electron microscopy (TEM) was used to investigate MSH microstructure. Compared with natural magnesium silicate hydrate minerals, the structure of MSH gel is highly disordered and generates on the surface of particles, producing a shell structure with cavity. The molecular structure of MSH phase is layered. The results also show that the extent of polymerization of MSH gel is related to the solution pH during hydration.

Note that "the structure of MSH gel is highly disordered and generates on the surface of particles", which means that the particles are inseparably coated with a thick layer of the gel, and that would account for the fact that they don't precipitate out -- or mix, for that matter.
posted by jamjam at 6:16 PM on August 8, 2021 [2 favorites]

Oh, and the silicate ions probably didn't come from the glass.

Sodium silicates are very common constituents of dishwasher detergents.
posted by jamjam at 6:44 PM on August 8, 2021

This happened to me with just vinegar and dish detergent, so the hard-water buildup might not be necessary. I think I used probably about an ounce of white vinegar and a few drops of Dawn Ultra dish detergent (ingredients), but it took some time to develop the pearlescent look.
posted by ectabo at 7:44 PM on August 8, 2021

Response by poster: The ingredients list on the dishwashing liquid does not include any silicates. (The photo isn't mine, but is of the label for the product I used.)
posted by Spathe Cadet at 7:08 AM on August 9, 2021