Science desk
< January 16	<< Dec \| January \| Feb >>	January 18 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 17

Taxonomic History of Mollusca

When were the very diverse Mollusca identified as a phylum? Our article on mollusca identifies them as having been identified in 1758, in the great 1758 edition of Systema Natura, but I further see that Linnaeus had identified the Mollusca as an order in the class Vermes. The phylum, as the highest-level division within the kingdom Animalia or Metazoa, wasn't defined by Linnaeus, only by Haeckel. (Linnaeus defined kingdom, class, order, genus, species. Family also came later.) So my question is when were the Mollusca defined as a distinct phylum? Also, were they always recognized as a distinct phylum? The various classes of molluscs are not obviously related except to a zoologist who is familiar with the mantle and mantle cavity. A clam, a snail, and an octopus certainly don't look alike. I see that Linnaeus evidently did recognize that they were a single taxon (but he saw almost everything). So what is the taxonomic history of the category of Mollusca? Robert McClenon (talk) 04:25, 17 January 2018 (UTC)[reply]

Haeckel introduced the term phylum in 1866. Abductive (reasoning) 07:41, 17 January 2018 (UTC)[reply]

Why is pittsburgh pa so cold?

In Pittsburgh today it is 11 degrees F. That's way colder than Boston, Bangor, Ithaca NY, and Burlington today, but it's way farther south. Is it random or does it happen a lot? Thanks. 144.35.45.59 (talk) 04:49, 17 January 2018 (UTC)[reply]

As a general rule, areas close to ocean coasts like Boston, and to a lesser extent, Bangor, Burlington and Ithaca have more moderate temperatures with fewer extremes, than inland areas like Pittsburgh. Ocean waters change temperature very slowly, whereas the land and the air can change temperature much more readily. So, nearby ocean waters act as a buffer to rapid changes in temperature. Please read this for more information. Cullen³²⁸ Let's discuss it 05:06, 17 January 2018 (UTC)[reply]

Ithaca isn't at all close to sea.144.35.45.59 (talk) 05:16, 17 January 2018 (UTC)[reply]

That is exactly why I said "to a lesser extent". Pittsburgh is roughly twice as far from the Atlantic Ocean than Ithaca is. And individual temperature readings on one day mean very little. If you take a look at historical average temperatures by month in that region, you will find that, in general, inland areas have more extreme variations than coastal areas. Cullen³²⁸ Let's discuss it 05:24, 17 January 2018 (UTC)[reply]

I suspect that when you compare Pittsburgh to Boston, the most salient factor explaining the difference in climate is each city's proximity to the ocean.

I suspect that when you compare Pittsburgh to Ithaca, the most salient factor explaining that difference in climate comes down to prevailing winds.

But in any given instance, we need to get some more details to understand what makes your town colder than the town 200 miles northeast.

If I was in a hurry, I'd just blast through the METAR:

KPIT ... 3045 ... T11441167

... and so on. That's quite compact, and I already know what I think is keeping you below freezing... but I'm heavily trained in interpreting weather, and the Government actually measures how rapidly I can spit back those weather-numbers! To the untrained eye, that number-soup carries very little information! Besides, we're in no hurry now - I've got a lot of spare time to think about weather at the moment!

As an avid enthusiast of the weather, I always start with the prog charts and surface analysis, and then I read the Forecast Discussion. In these special technical weather service products, the chief meteorologist on duty in your area will explain in great detail what they're observing, why they think it's happening, and how their analysis is informed by technology, including computer climate models. It tells you not only what the weather's doing, but why it's doing it, and how we know.

For example, today in Central New York:

“

The combined effects of a slow moving upper-level trough, favorable upper jet entrance region dynamics, and a moist S-SW flow over a deep layer, continue to bring light-moderate snow to NEPA and much of CNY this evening. At the same time, there appears to be a bit of a disconnect between the layer of best forced lift and the dendrite growth zone, resulting in fairly small crystals/snowflakes for most locales and accumulation efficiency not quite as good as it could be.

”

And in Pittsburgh:

“

A lowering temperature inversion and decreasing moisture should end this by morning. Maintained current advisories as is for now with the snow ongoing. Otherwise, patchy stratocu with upper troughing and cold advection should affect the area tonight. Lows should be around zero.

”

And Boston:

“

More substantial snowfall is expected starting this evening into tonight, as a coastal low pressure system is forecast to emerge off the Delmarva and track northeast along a baroclinic zone close to the NJ/Long Island coast. At the same time, the positive tilt mid/upper level trough will migrate eastward. Appears that a transfer of energy as coastal low jet structure begins to take hold early tomorrow morning will help phase the clipper system. This coastal low track has been key for this forecast as it is projected to track across the Cape and up towards the Maritimes. At the same time, open wave at 700 mb and surface high situated over the Maritimes will help allow the warm air to push into southern New England. The lack of blocking, also allows for this system to be quite progressive.

”

Wow, that's a lot of atmospheric science, delivered straight up from a real actual atmospheric scientist!

When you get into the Forecast Discussions, you start to recognize that the air and atmosphere are a giant system, and when it's cold on the ground in Pittsburgh, it's because Earth's atmosphere is doing something special somewhere else. At this very moment, Pittsburgh is colder than the cities north of it because you're behind the front. Your cold air is too low-pressure to blast into Ithaca; for now, a slug of cold air is trapped near the ground in western Pennsylvania, even though it looks like in the next few days, your cold air is going to ride over the top of their airmass. In the short term, their cloud cover is going to hold in some thermal energy, and they'll soon be mixing in more heat out of the Atlantic over the next few days. But, it's the Northeast - it's really dynamic and anything could change! I spent the first few days of 2018 travelling the Eastern seaboard, convinced that the giant high pressure slug three thousand miles wide was totally impenetrable, and ... whack! A surprise hundred knot high level wind killed our blue skies from totally the opposite direction!

If you love weather, and need more than just the conditions forecast, learn to know and use the Area Forecast Discussion!

Nimur (talk) 05:54, 17 January 2018 (UTC)[reply]

Pittsburgh is also west of the Appalachians, there is little land relief holding off an Arctic blast compared to more northernly coastal areas. μηδείς (talk) 03:14, 18 January 2018 (UTC)[reply]

It's west of most Appalachiany stuff, not all. I've been there and there's freaking cliffs/near cliffs everywhere. Okay not everywhere but the Greyhound goes through a tunnel through the cliff right outside downtown just to get in and there's many bridges over valleys or inclined rail-like things (see image) from the steep(ish) elevation drops of hundreds of feet impeding metro area connectivity so much. Sagittarian Milky Way (talk) 06:32, 18 January 2018 (UTC)[reply]

Yes, it's just barely southeast of the line between the glaciated and unglaciated sections of the Allegheny Plateau. There's virtually nothing to obstruct the passage of weather from the northwest. Nyttend (talk) 13:36, 18 January 2018 (UTC)[reply]

I didn't say hundreds of feet of relief was enough to obstruct the weather, I just expected the site to be less hilly and have wider riverplains since it's so west and big. Perhaps Philly had a financial interest to make it bigger while trying to copy the Erie Canal? Perhaps the hilliness was a benefit since it meant nearby fossil fuels for the factories? I wonder if Burlington would've been at least a degree Fahrenheit warmer that day if the gaps in the Appalachians at the Burlington to Montreal and Mohawk River routes didn't exist. Sagittarian Milky Way (talk) 01:39, 19 January 2018 (UTC)[reply]

Here's an archived map showing the cold front Nimur mentioned. Sagittarian Milky Way (talk) 01:39, 19 January 2018 (UTC)[reply]

Chemistry question.

Is it a contradiction to be a strong Lewis acid (receive electrons) and a strong reducing agent (loses electrons) at the same time? And is it a contradiction to be a strong Lewis base (loses electrons) and a strong oxidizing agent (causes others to lose electrons) at the same time? Can anyone list any molecular examples? Thanks. 12.130.157.65 (talk) 15:33, 17 January 2018 (UTC).[reply]

Hydrogen iodide is a strong acid and a strong reducing agent. This Chemistry Stack Exchange question and answer may be of interest. Double sharp (talk) 15:50, 17 January 2018 (UTC)[reply]

Okay here's my list.

Strong acids and strong oxidizing: HNO3, H2SeO4, CrO3, H2SO4, HMnO4, HClO4, OsO4, RuO4.

Strong acids and strong reducing: HI.

Strong bases and strong oxidizing: none.

Strong bases and strong reducing: LiH, NaH, CaH2, MgH2.

12.130.157.65 (talk) 14:38, 18 January 2018 (UTC).[reply]

Sodium peroxide is a strong base and oxidant. DMacks (talk) 22:04, 19 January 2018 (UTC)[reply]

Various iron(II) compounds are a prototypical example of a metal cation that is in the lower of several common oxidiation states for that metal. It is a fairly good reducing agent, becoming the more stable iron(III) species (see iron(II) sulfate), and it is a Lewis acid because it is cationic with many open coordination sites (notice the many Coordination complex of it; doi:10.1021/cr040664h has many examples of reactions involving Lewis aciditity anddoi:10.1002/cctc.201402029 is an interesting recent example). DMacks (talk) 16:01, 17 January 2018 (UTC)[reply]

Then if I follow the pattern, can I generalize, metal ions in their lowest oxidation state? 12.130.157.65 (talk) 14:38, 18 January 2018 (UTC).[reply]

doi:10.1021/ed019p24 is a J. Chem. Educ. article discussing the parallels of the two concepts from first principles. DMacks (talk) 18:18, 18 January 2018 (UTC)[reply]

Damn, that article dated 1942. I'd trust it if it were in the '70s though. Not even Linus Pauling's book dated 1970 (which a lot of gen chem textbooks base categorizing off) covers this subject? And Linus Pauling has since updated his 1st 1970 book. 12.130.157.65 (talk) 16:42, 20 January 2018 (UTC).[reply]

When I look at the article reducing agent I see I'm more confused than I expected. My impression is that a "true" reducing agent can be written as participating in a half-reaction that releases electrons, while the thing reduced gets only the electrons and nothing else. But our article calls glucose being respired in the presence of oxygen a reducing agent. Now this is relevant to a redox reaction, and the oxygen does get reduced ... but without a clean model for transferring electrons, it does seem to vary from the simplest situation, while you could try to call the oxygen a Lewis acid and the CO2 a Lewis adduct, of a sort ... to be clear, that's not a way I've ever heard it put though. But is there a way to explain why things are put this way, or is it just a habit of speech? Wnt (talk) 13:18, 20 January 2018 (UTC)[reply]

And our article on oxidizing agent defines it as causing others to lose electrons, but doesn't infer it has to receive those electrons, do we assume it does? If not, where do the electrons go. And examples can include bacteria, oxidizers destruct bacteria so causes them to lose electrons. 12.130.157.65 (talk) 16:44, 20 January 2018 (UTC).[reply]

The idea of simply transferring a whole electron from one atom to another, for example:

Fe²⁺ + Cu²⁺ → Fe³⁺ + Cu⁺

is how the more general idea of oxidation state can be simplified when talking about lone atoms. DMacks (talk) 19:58, 20 January 2018 (UTC)[reply]

That does seem like the only way to go with this, so let's test it out: sodium peroxide in water should react Na2O2 + 2 H2O -> H2O2 + 2NaOH. [sorry, didn't balance that right] In this scenario Na+ doesn't oxidize/reduce anything, (O2)2- becomes H2O2 with no oxidation/reduction at the oxygen which stays in a -1 oxidation state, H stays at +1 the whole time, O in water/OH- is at -2 the whole time. So there it is not an oxidizing agent but it *is* a Lewis base. Whereas with Na2O2 + CO2 -> Na2CO3 + 1/2 O2, the Na+ is always +1, (O2)2- goes from -1 to 0 oxidation state in O2 and -2 oxidation state in (CO3)2-, C stays at +4... oh shoot, is that even acting as an oxidizing agent at all? If I strike an average O stays at -1 the whole time. I suppose the decomposition of hydrogen peroxide (equivalent to this reaction in water) cannot be a redox reaction. ;) I suppose I actually have to *bleach* something with that (O2)2- so there is no oxygen emitted, and then I can say the oxygen goes from -1 to -2 and the other thing goes more positive. Wnt (talk) 01:46, 22 January 2018 (UTC)[reply]

Wnt, your equation Na2O2 + H2O -> H2O2 + 2NaOH is unbalanced and incorrect. The correct equation would be 2 Na
₂O
₂ + 2 H
₂O → O
₂ + 4 NaOH and it is a redox process and an example of disproportionation. The peroxide ion is both oxidised to elemental oxygen and reduced to the hydroxide ion. Your sodium peroxide plus carbon dioxide reaction is also a disroportionation – the peroxide is oxidised to oxygen and reduced to oxide, which undergoes a Lewis acid / base reaction with carbon dioxide to form the carbonate ion. Hydrogen peroxide disproportionation to water and oxygen is also a redox reaction. Oxygen in compounds typically has the oxidation state -2... the -1 state in peroxide is uncommon and highly reactive. EdChem (talk) 09:41, 23 January 2018 (UTC)[reply]

PS: A reducing agent is a substance which causes reduction and is itself oxidised in the process. Considering the case of glucose + oxygen → carbon dioxide + water. Oxygen is the oxidising agent as it causes the glucose to be oxidised (C in glucose in oxidation state 0 becomes carbon dioxide with carbon in the +4 state) and is itself reduced (elemental oxygen has O atoms in oxidation state 0 and becomes oxidation state -2 in water). However, I can look at it the other way – glucose is the reducing agent as it causes oxygen to be reduced (O in OS 0 to O in H
₂O in OS -2) and is itself oxidised in the process (C in OS 0 in glucose to C in OS +4 in CO
₂). EdChem (talk) 09:48, 23 January 2018 (UTC)[reply]

Actually I was just protonating the (O2)2- there simply to illustrate Na2O2 is a base, but I did omit the 2 I've now added in bold above. Wnt (talk) 12:22, 23 January 2018 (UTC)[reply]

Ok, Wnt, I see what you meant, but our equations end up at the same place due to disproportionation of hydrogen peroxide:

Eqn 1: Na
₂O
₂ + 2 H
₂O → H
₂O
₂ + 2 NaOH

Eqn 2: 2 H
₂O
₂ → 2 H
₂O + O
₂

Overall: 2 x Eqn 1 + Eqn 2: 2 Na
₂O
₂ + 2 H
₂O → O
₂ + 4 NaOH

Essentially, putting peroxide ions (from Na
₂O
₂) into water allows both Brønsted–Lowry acid / base proton transfer reactions (producing both hydroperoxide anions and hydrogen peroxide) and redox disproportionation. Both processes will occur, overall leading to hydroxide ions and oxygen gas and an equilibrium system in solution.

As for 2 Na
₂O
₂ + 2 CO
₂ → 2 Na
₂CO
₃ + O
₂, it is a redox process and yet another disproportionation with the oxygen from the peroxide both oxidised to oxygen gas and reduced to oxide ions which are incorporated into the carbonate. I hope this and the explanation of a reducing agent makes sense. EdChem (talk) 21:06, 23 January 2018 (UTC)[reply]

Accelerating radioactivity naturally decay

Can you accelerate radioactivity naturally decay of atomic waste, instead of waiting millennia until it's harmless? --Hofhof (talk) 19:41, 17 January 2018 (UTC)[reply]

No, see Radioactive_decay#Radioactive_decay_rates - for any one isotope of any particular element, the equations are governed by constants. Mikenorton (talk) 20:05, 17 January 2018 (UTC)[reply]

Well, Radioactive_decay#Changing_decay_rates. But not really practical. DMacks (talk) 20:07, 17 January 2018 (UTC)[reply]

Besides, decay rates only change noticeably with environment for ⁷Be (an L-capturer where the captured electrons are also the valence electrons) and some cases where the decay energy is tiny (for example, nuclides in this position cannot undergo internal conversion with the inner electrons, but only on the outer valence electrons). Most fission products and actinides don't fall into either of these groups; actually I am not sure if any do, since fission products are neutron-rich, and electron capturers must perforce be neutron-poor, so you'd mostly have to look for gamma emitters. (Is ^99mTc a significant fission product? Its ground state certainly is, but I don't know about the metastable state. If so it would be an example, but note that the decay rate changes produced by such means don't usually even get close to 1%.) Double sharp (talk) 08:23, 18 January 2018 (UTC)[reply]

Double sharp, ^99mTc is not a significant fission product, but ⁹⁹Mo is and it undergoes β-decay to ^99mTc. Collection ⁹⁹Mo, adsorbing it onto a column, and then eluting to milk the cow is a standard source of ^99mTc for medical applications. EdChem (talk) 09:56, 23 January 2018 (UTC)[reply]

@EdChem: Thanks for the info! So ^99mTc will not be produced directly in significant quantities, but it will occur anyway as the daughter of ⁹⁹Mo, which is. Well, we have our example, then. ^_^ Double sharp (talk) 10:09, 23 January 2018 (UTC)[reply]

You can't really change the decay rate of any particular type of nuclear waste, but you can (sometimes) bombard it with neutrons to convert the waste into different isotopes, which may have a faster decay rate. See Nuclear transmutation#Artificial transmutation of nuclear waste. PiusImpavidus (talk) 20:22, 17 January 2018 (UTC)[reply]

Also Radioactive waste#Transmutation. -165.234.252.11 (talk) 20:24, 17 January 2018 (UTC)[reply]

A Breeder reactor creates less waste because it burns up some of what would otherwise be waste. You might also be interested in the rather strange Quantum Zeno effect which does the opposite - though it is not practical as a way of stoping radioactivity. Dmcq (talk) 23:10, 17 January 2018 (UTC)[reply]