Wikipedia:Reference desk/Archives/Science/2019 August 29

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August 29

Scented bleach

How is the lemon scent, etc., not oxidized and destroyed by the bleach ? SinisterLefty (talk) 00:14, 29 August 2019 (UTC)

Not all chemicals are oxidizable by hypochlorite (the usual chemical in traditional "bleach"), and there are alternate bleaching agents that can/can't react with different sets of chemicals. Looking at the ton of different chemicals that Clorox might use as fragrance, I see a lot that don't have any obvious reactivity with hypochlorite...ketones, esters, carboxylic acids, and phenols for example. DMacks (talk) 00:36, 29 August 2019 (UTC)

Thanks. Does that mean any microbes could evolve a shell of any of those chemicals, and thus survive exposure to bleach ? SinisterLefty (talk) 01:26, 29 August 2019 (UTC)

At least become more resistant, sure. Can't remember which HSP is especially activated in response (hypochlorite is part of our immune system). And some can form films that protect their colonies. DMacks (talk) 02:13, 29 August 2019 (UTC)

Also, that's assuming that these compounds are in any way suitable to making these "shells." I would guess that they are not. --OuroborosCobra (talk) 15:46, 29 August 2019 (UTC)

Citrus scented chlorine bleaches usually contain limonene, which does react with both chlorine and hypochlorite. However, this reaction apparently proceeds at a very slow rate, if at all, when the pH of the solutions and concentrations of bleach and limonene are kept at certain values. Here is one patent that describes some experiments in this [1], though they do not really explain the chemistry. There is an abundance of chemistry papers describing the halogenation of limonene, but I cannot locate any that tried to find or explain conditions where the reaction didn't happen. Someguy1221 (talk) 01:23, 29 August 2019 (UTC)

I still painfully remember a failed test in chemistry for having disregarded chemical kinetics Gem fr (talk) 01:28, 29 August 2019 (UTC)

An experiment that disregards chemical kinetics could be far more painful, say if you tossed a large quantity of elemental sodium into water: [2]. SinisterLefty (talk) 16:14, 29 August 2019 (UTC)

Jesus. Someone strike this video of a man holding sodium with bare hand. Not that dangerous, not such disregard of basic security measure is just ... Gem fr (talk) 18:55, 29 August 2019 (UTC)

Yes, I wondered why it didn't react with the moisture on his hands, but I assume it has an oil coating to prevent that. That might be why they had to cut it, to expose the sodium, for the "experiement". SinisterLefty (talk) 14:32, 30 August 2019 (UTC)

It's a matter of how much scent remains after a reasonable shelf life, I guess. Remember, most scents work in micromolar quantities, so it's possible to load a gallon of bleach up with enough scent at manufacture that while in use it keeps its scent despite some of it reacting with the hypochlorous acid continually. --loupgarous (talk) 02:16, 29 August 2019 (UTC)

"loading bleach up with enough scent" won't help. There is so much oxidizer in bleach (that is the very point of bleach) that, if the reaction proceeds, you cannot rely on a large enough supply of scent to have some of it survive. Only low speed of the oxidation makes it possible. Gem fr (talk) 18:11, 29 August 2019 (UTC)

In the case of limonene, this actually can't work, as the space between "so dilute it's basically useless" and "so concentrated it's overwhelming" is surprisingly narrow, at least in straightforward bleach solutions. Someguy1221 (talk) 08:18, 30 August 2019 (UTC)

I don't know why cleaning chemical companies even bother, it doesn't reduce their shit smell for me. Reminds me of some baby boomers who wear perfume so strong and laden with chemical notes that I'm amazed they attract more men that way. Some of their pheromones even attract me and they're utterly hiding them with that crap. Sagittarian Milky Way (talk) 14:12, 29 August 2019 (UTC)

People buy it, they sell. Plus, they charge more, not significantly more for the buyer, but significantly more than the cost of the scent. Bleach is so inexpensive, the margin are so small, anything boosting the profit is good enough.

Gem fr (talk) 18:11, 29 August 2019 (UTC)

Did they do mopping tests on which pleasant smelling chemicals make bleach smell least bad? I guess that's the best they can do that isn't too expensive? I just use isopropanol when I want something cleaned to the point of disinfection. Smells better. They make isopropanol sprays too. Refill it with more isopropanol so you only have to be overcharged for the spray bottle once. They make it hard to open but it can be done. Sagittarian Milky Way (talk) 01:05, 30 August 2019 (UTC)

In the case of citrus smells, the fragrance molecules are also surfactants, and will dissolve oils off of many surfaces. They'll call it "scented", but the scent was going to be there anyway given what the active ingredients are. Someguy1221 (talk) 08:24, 30 August 2019 (UTC)

Makes sense. I forgot about the lack of hydrophobic parts. Even shaving cream has hydrophobic parts. Sagittarian Milky Way (talk) 12:36, 30 August 2019 (UTC)

There's another reason not to make bleach smell good. You shouldn't remain in a room with bleach fumes, as that's bad for the lungs. So, they might even consider adding a foul smell, to drive people away, like in natural gas. A nice smell that gets people to stay there seems unwise. SinisterLefty (talk) 14:28, 30 August 2019 (UTC)

Thanks all. SinisterLefty (talk) 00:46, 3 September 2019 (UTC)

Bright, shiny objects

Huge hoard of Norman coins found in Somerset shows coins being plucked from the ground in remarkably (suspiciously, to me) shiny condition. Is it possible that coins from Norman England (c.800+ years ago) would remain in such condition? What sort of alloy would they have used? If they were primarily silver, wouldn't they essentially be black blobs by now? Secondarily, most of the whole coins seem to be bent in the middle, with many others being split in half; was it common to split coins ("ha'penny")? 2606:A000:1126:28D:C11B:68F2:2FB:1B34 (talk) 18:24, 29 August 2019 (UTC)

The conservation of silver coins depends on the soil, and silver resist pretty well to oxydation (not as well as gold, but, still) (one of the reason to make coins out of it) so you may want to check the soil, but not suspicious per se. Bending coins was a way to check they were legit. Splitting coins was common enough https://www.cointalk.com/threads/medieval-cut-pennies.266902/ Gem fr (talk) 19:14, 29 August 2019 (UTC)

Most of silver tarnish is caused by hydrogen sulfide and some soils are practically anoxic. So leaving it in the same room as an egg or fart might be worse than leaving it outside in a wilderness. Sagittarian Milky Way (talk) 23:53, 29 August 2019 (UTC)

Indeed, there are soils in which silver remains untarnished by sulfur, varying by local ph and redox potential. See [3] on the conditions required for the oxidation of silver, and [4] for a neat graph showing the typical range of soil properties. Someguy1221 (talk) 08:11, 30 August 2019 (UTC)