Wikipedia:Reference desk/Archives/Science/2021 September 22

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September 22

Measure oxygen concentration

I want to test an oxygen concentrator for purity of the oxygen coming out. Any idea how to do that? It gives a slow, low pressure stream of oxygen coming out of a tube. Holding a lit match near the output makes the flame flare up a little, but it's not dramatic. Is there another simple test? Thanks. 67.164.113.165 (talk) 03:21, 22 September 2021 (UTC)

I once worked for a company where there was an instrument that measured that, for O2 and CO2. It had a thin needle to measure, and ran for a few seconds, then outputted a number. They said the instrument was worth $5,000. Maybe you can search on-line for such an instrument, but I'm not the right person to help get you started. 67.165.185.178 (talk) 07:50, 22 September 2021 (UTC).

A hand-held scuba nitrox analyser will give you the Oxygen fraction to within about 0.1% and you can probably find one for around €120. If you're handy with a soldering iron you could make your own for a fraction of that. 2A01:E34:EF5E:4640:A028:DB79:13E4:2403 (talk) 12:20, 22 September 2021 (UTC)

The article that discusses the equipment is oxygen analyser. There seems to be plenty of choice. Mike Turnbull (talk) 15:07, 22 September 2021 (UTC)

Those are indeed the general type of equipment. The specific analysers shown in the article are trimix analysers which also measure the fraction of helium, making them much more expensive creatures though. As discussed in the article, the underlying principle is to measure the current output of a galvanic cell across a load resistor, so if you're not too worried about high precision you can just use a voltmeter. 2A01:E34:EF5E:4640:A028:DB79:13E4:2403 (talk) 15:16, 22 September 2021 (UTC)

Thanks, I found a few articles about DIY nitrox analyzers for scuba, whose main ingredient appears to be an O2 sensor that costs around $80. I'll look around for less expensive ones. They have a shelf life, so maybe a dive shop could have some expired ones around. You are right that I don't need a precise measurement. 2601:648:8202:350:0:0:0:1598 (talk) 18:37, 22 September 2021 (UTC)

A good source for used cells is rebreather divers as they change their cells well before the notional expiry. A dive shop will probably be able to put you in touch.

At the O2 partial pressures you're looking at, even a used cell is really very linear so the minimal circuit is really nothing more than a load resistor and a voltmeter. You'll need to calibrate with two known gases (typically air and pure Oxygen), ideally before each use.2A01:E34:EF5E:4640:3D07:C0BA:6A0F:BFCF (talk) 20:13, 22 September 2021 (UTC)

Thanks, I'll have to figure out where to get pure oxygen in this case. I remember separating out hydrogen by water electrolysis in school, but not oxygen. Come to think of it, I have no idea where the oxygen goes when the hydrogen bubbles up. I guess there are places that sell oxygen in cans though. 2601:648:8202:350:0:0:0:1598 (talk) 21:10, 22 September 2021 (UTC)

You may be able to get hydrogen peroxide or peroxide bleach, and bubble off some fairly pure oxygen gas, if you don't want to purchase an oxygen cylinder. It may still contain water vapour or traces of atmosphere. Graeme Bartlett (talk) 12:45, 24 September 2021 (UTC)

You could also measure oxygen by capturing the gas above water, and then oxidising something that will use up the oxygen. eg rusting iron, or burning magnesium. Then measure how much volume has reduced once temperature returns to normal. Burning things that make gas will not change the volume that simply. Graeme Bartlett (talk) 12:48, 24 September 2021 (UTC)

Making steel from Fe(II) instead of Fe(III).

Steel is currently Fe(III). What would be the problem for trying to make steel from Fe(II). Need a counter-anion? Sure, then make a counter-anion. Would that work? What would be the problem for trying to make steel from Fe(0) to Fe(II)? 67.165.185.178 (talk) 07:52, 22 September 2021 (UTC).

Steel is not Fe(III). I'm not sure where you got that from. Steel contains atomic iron, Fe(0) if you will. It is an alloy of iron and carbon and sometimes other trace metals. Alloys are not ionic compounds, they are elemental mixtures. The rest of your question cannot be answered because it was based on a false premise. --Jayron32 12:01, 22 September 2021 (UTC)

On the other hand, steel ultimately comes from iron ore and as that article suggests some of the ore is indeed Fe(II) (for example siderite) while others are Fe(III) (for example hematite). Whatever the ultimate source of the iron, the process involves chemical reduction to Fe(0) by smelting or direct reduction. The standard reducing agent is carbon, normally in the form of coke, as this is cheap and readily available. A proportion of the carbon may be left in the iron, forming steel. Mike Turnbull (talk) 14:59, 22 September 2021 (UTC)

It looks like the OP has changed their question. Fe(II) is an ion and does not exist in nature unless it is part of an ionic compound, like iron (II) chloride or iron (II) sulfate, or the aforementioned siderate (iron (II)) carbonate). Ionic compounds are not metallic in nature, and would not have any of the properties of neutral metals. The oxidizing of Fe(0) to its ionic forms such as Fe(II) and Fe(III) is a common reaction, it creates rust. So, if you convert the Fe(0) to Fe(II), you don't get a different form of steel, you get a black, crumbly powder such as iron (II) oxide. --Jayron32 15:50, 22 September 2021 (UTC)

So you guys say iron(II) does not exist in nature except with ionic compounds, or did you just mean in liquid solution? I was thinking of carbon monoxide binding to the Fe(II) in hemoglobin, at a 210x greater rate than O2. If there is CO next to siderite, it won't be able to break the FeCO3 bond so Fe(II) reacts with CO like it does in the body? 67.165.185.178 (talk) 08:49, 24 September 2021 (UTC).

No, iron (II) is not a metal. It is an ion, and ions are ONLY part of ionic compounds, whether solid or in solution. If you react iron (II) with carbon monoxide, you'll likely get a complex ion, like Fe(CO)₄²⁺, known as the tetracarbonyl iron (II) ion, which I can find some examples of in literature. This is still not metallic and still will not form as part of an alloy. --Jayron32 11:11, 24 September 2021 (UTC)

The iron oxide article is sadly one of those that need blowing up and starting again from scratch. It's not actually misinformative, but it lacks such large amounts of basic information that anyone reading it would tend to get the wrong idea. Mike Turnbull is right in saying that whatever the mineral form of iron, such as magnetite (Fe₃O₄ Iron(II,III) oxide), hematite (Fe₂O₃ iron(III) oxide), or siderite (FeCO₃ iron(II) carbonate) the bonds it forms within the compounds are broken down at high temperature during the smelting process, resulting in effectively pure iron, Fe(0) or ferrite. See also Allotropes of iron.

During the conversion from pure iron to steel, small quantities of the much smaller carbon atoms dissolve into the molten crystal structure of the iron, effectively filling the gaps between the iron atoms. On cooling this forms cementite or iron carbide (Fe₃C), an intermetallic compound which gives the alloyed steel its hardness. Iron can only absorb a certain amount of carbon: as more is added, graphite is formed outside the cementite, making cast iron which is a mixture rather than an alloy.

It doesn't matter what type of iron ore you start with as long as it's economically viable. Some ores have very low concentrations of metallic iron, such as Taconite (thin bands of magnetite at 25%), but the vast sandy beds in the Minnesota/Lake Superior region make surface mining very easy. On the other hand, the Carajás Mine, Brazil, contains hematite at up to 65% metallic iron. The deep Dannemora mine, Sweden, used to have amazingly pure magnetite ore - up to 95% or more metallic iron, but such rich deposits have all been mined out. MinorProphet (talk) 00:07, 30 September 2021 (UTC)

Sneezing into a respirator

After an open-mouthed sneeze into a respirator, does it need to be replaced right away or at the end of the day? Thank you. Imagine Reason (talk) 12:57, 22 September 2021 (UTC)

Maybe it depends on how bad the sneeze was? Other than that, wouldn't you just be inhaling your own germs anyway? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:27, 22 September 2021 (UTC)

One issue could be expelled fluid messing up the electrostatic layer in the respirator. I don't know how that would mess it up more than moisture buildup from normal exhaled air already would though. They do always tell you not to wash and re-use respirators. Another issue in a medical context might be that the respirator is full of germs that you are now exhaling onto a surgery patient or something. 2601:648:8202:350:0:0:0:1598 (talk) 18:40, 22 September 2021 (UTC)

Yes, that's what I'm concerned about, whether it counts as the respirator getting wet. It is, ounce for ounce, more water than you'd expect from breath, no? It's not in a medical context. Imagine Reason (talk) 23:23, 22 September 2021 (UTC)

I'm not sure but I think the damage from washing the electrostatic layer may come from exposure to soap, rather than moisture per se. I know that during the big N95 shortage, medical people kept re-using them for weeks. There was at least some evidence that they stayed effective through re-use. Heating them in an oven (autoclave?) was also supposed to be an ok way to sterilize them. 2601:648:8202:350:0:0:0:1598 (talk) 18:44, 24 September 2021 (UTC)

Thousands of doctors and nurses were infected last year, while many places in East Asia, like Hong Kong, Taiwan, and Singapore, saw zero such infections. I've read accounts of medical professionals getting infected after reusing masks. The CDC has found that they should be discarded after five donnings because of fit. No, it's not just soap that damages respirators. Water will do. It's advised that you discard them after they get wet. My question is, what constitutes getting wet. Imagine Reason (talk) 01:27, 26 September 2021 (UTC)