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I am not a chemist! My chemistry classes from my molecular biology undergrad are far behind me. But I think I created a salt, and I don't know how. Here is my mystery:

I recently got some water in my car, and wanted to prevent mold growth in my carpet mats. I brought the mats inside, vacuumed off, and completely soaked them in household vinegar. Then I placed the mats near a running dehumidifier (where the warm air comes out in the back).

White crust appeared on the carpet. At first I thought my dehumidifier was spitting something out, but the white substance was not on any other nearby surface--only on the car carpet. Eventually as the further parts of the carpet dried, they also showed the white crust. It covers pretty much all of the carpet.

Is this, in fact, a salt? If so, what basic substance could have been in my car carpet mat that would cause this reaction? Thanks everyone!

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  • $\begingroup$ Was a cleaner with baking soda ever applied to the mat? $\endgroup$ – Brinn Belyea Jul 22 '14 at 21:24
  • $\begingroup$ @brinnb Not to my knowledge (at least not in the last few years). Also, there was no noticeable bubbling when I poured the vinegar over the mat. It seemed to be the application of the heat/dry air from the dehumidifier that catalyzed the reaction. $\endgroup$ – Becky Jul 22 '14 at 21:48
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    $\begingroup$ Is the powder water soluble? If you heat it in a blowtorch flame what color is it? $\endgroup$ – Brinn Belyea Jul 23 '14 at 1:21
  • $\begingroup$ @brinnb I can check solubility in water tonight. But I don't own a blow torch or anything resembling it! $\endgroup$ – Becky Jul 23 '14 at 14:49
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    $\begingroup$ The powder is water soluble. $\endgroup$ – Becky Jul 24 '14 at 15:30
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I once had a humidifier and I ran it with tap water. I soon noticed a build up of white dust on the carpet right in front of the humidifier. I suspect your situation might be related to what caused my white dust. Tap water contains salts (just like table salt), the harder the water the more salts it contains. They are present in low concentration so you don't normally see them. In my case, as more and more tap water evaporated it led to a visible build up of these salts. In your case, as the water on the carpet dried, it left behind the same salts. Maybe you really soaked your carpet with a lot of water, maybe your water is very hard, and finally, maybe salts were actually put into the carpet during their manufacturing process - and maybe washing them with vinegar (dilute acetic acid) solubilized the salts and brought them to the surface, making them visible upon drying.

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    $\begingroup$ I see what you're getting at, but it doesn't fit all the pieces together for me. I never applied tap water to the carpet. The only liquid applied to it was my vinegar, and before that, the rain/runoff water that flooded my car. I live down south, so the roads here aren't salted. I'm processing as I go here... I used to live way up north where winter was long and there was a lot of salt on roads and sidewalks, which my shoes would have easily transferred to car carpet. Could that have been what the vinegar solubilized? $\endgroup$ – Becky Jul 24 '14 at 15:34
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    $\begingroup$ I suspect that the runoff water that flooded your car has a lot more salt content than your tap water. I'm guessing it was runoff salt and salts from the carpet manufacturing process. $\endgroup$ – ron Jul 24 '14 at 16:23
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    $\begingroup$ I know "salt" is very general term--but what salts would there be in runoff water if the roads are never salted due to winter weather? Do lawn chemicals contain salts? $\endgroup$ – Becky Jul 24 '14 at 18:07
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    $\begingroup$ You bet, fertilizers are a big contributor, road degradation, car emissions and degradation products from brake pad linings also contribute. $\endgroup$ – ron Jul 24 '14 at 18:13

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