Wikipedia:Reference desk/Archives/Science/2019 July 6

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July 6

composition

Pure substance have a fixed composition i.e., for water it is 1:8 (hydrogen:oxygen). An element is a pure substance, but how does it has ratio of its atoms in its lattice i.e., How to define element's chemical composition? Suyogya1 (talk) 02:50, 6 July 2019 (UTC)

There are single element molecules, like H₂ (diatomic hydrogen gas). Then there are crystals made of a single element, like diamond, made of carbon. To determine the density of such a crystal, you need to determine which type of crystal lattice it forms. Each has a characteristic percentage occupied by atoms, and the rest is empty. Of course, these empty spaces also need to be considered in determining the density of crystals made of two or more elements, like table salt crystals (NaCl). And obviously the density of the atoms also plays a role. And in the case of hollow crystals, like buckyballs/fullerene and buckytubes/carbon nanotubes, the contents, if any, of the hollow spaces must also be considered. SinisterLefty (talk) 03:36, 6 July 2019 (UTC)

Strange question. The "lattice" is not an element, it makes no sense to compare the 1:8 (hydrogen:oxygen) mass ratio of water, to the "ratio of its atoms in its lattice". For a pure element (like: a simple copper wire), the mass ratio is simply 1:1. Now, crystallography does define something which may be what you are looking for: crystal system. You may find lattice constant of interest, too. Or may beyou are just looking for density? Gem fr (talk) 07:12, 6 July 2019 (UTC)

Yellow substance from tomatoes

Dears users of en.wikipedia, good morning. I try to write to you a question in my bad English, sorry for the grammar errors.

In my house garden I cultivate tomatoes. Every time I pick up the tomatoes from the plant, a yellow and powdery substance remains in my hands. I can remove this substance only with the Marseille soap degreaser. Someone can tell me what is the name of this substance. Thank you for the attention.

--87.8.151.65 (talk) 10:44, 6 July 2019 (UTC)

Could it be Pollen? The waxes and proteins on the surface of the granules can make it difficult to remove. Dbfirs 10:54, 6 July 2019 (UTC)

Is it possible? Can the pollen be on all surface of the skin of sigle tomato? On Google I find the tomato tar, but for my low knowledge the tar is the thing with which streets and roads are made, and seems a slang word to indicate something (pollen?). Thank you Dbfirs for answer me.--87.8.151.65 (talk) 12:07, 6 July 2019 (UTC)

If it's on the surface of the tomato, then pollen seems unlikely. Dbfirs 06:20, 7 July 2019 (UTC)

Yes, tomato tar seems to be the answer: [1]. That is an unusual usage of the word "tar", I agree, probably because it's sticky like tar. Here's more on the cause and how to remove it: [2]. It seems to be acid-soluble and serves the function of sticking to insects to drive them away. If anyone feels like making an article, those two links would be a good start. SinisterLefty (talk) 12:19, 6 July 2019 (UTC)

Wow, I know exactly what the OP means, but have never been inspired to find out more. SinisterLefty above has pinned it down. I also found this - [3]. It has lots of details. One bit says "These substances are thought to protect plants against environmental assaults including insect attacks, foliar diseases, extreme heat and excessive light." I have always thought of the stuff as being green, rather than yellow, but I can tell we're talking about the same thing. For washing it off, I use a product known here in Australia as Solvol, again something I've never thought much about, and a look around on the web tells me it's not known by that name elsewhere. I don't know what it might be called. It has bits of ground pumice in a soap bar. Not as hard on your skin as it might sound. Good luck finding your local equivalent. HiLo48 (talk) 12:38, 6 July 2019 (UTC)

ADDENDUM: It seems that Lava (soap) might be the equivalent American product to what I know as Solvol. HiLo48 (talk) 12:45, 6 July 2019 (UTC)

My second source suggests using vinegar, since it's acid-soluble. Might be less harsh on the hands. Tomato tar also seems to change colors when it reacts with various chemicals found in cleaning products, ranging from yellow to green to brown to black. And of course it will look different on a red or green tomato than on a white towel. SinisterLefty (talk) 13:00, 6 July 2019 (UTC)

May be previous answer are good, but my first thought was you are facing some pest. In my mind, yellow+sticky prompts: Scale insect. I'll browse your favorite pest-control Internet resource if I were you. Gem fr (talk) 14:23, 6 July 2019 (UTC)

DNA Replication Video cont´d

Version 2

DNA Replication / Video Version 2 ad user:wnt, user:DMacks et al

Based on the comments by the users wnt and DMacks I have implemented the subsequent modifications to my original model from 26.06.2019:
1 As per wnt: The enzyme helicase only unwinds a short portion of the double helix to generate a “flat” molecular section for further replicative steps. The remaining part of the DNA remains coiled in the form of a double helix.
2 As per DMacks: In the replicative phase I have shown the nucleobases A/T/C/G (represented by differently coloured sticks) being synthesised in their proper sequence as determined by the pre-existing nucleobases on the leading / lagging strands.
3 As per DMacks: I have replaced the original backbones (which were shown as tubular helices) with individual balls. I have used different colours to indicate the antiparallel directionalities (3´- 5´ vs 5´- 3´) on the leading vs lagging strands. DMacks has suggested arrows for this purpose, but I was unable to achieve that.

? Is it permissible to include an existing WP image in the movie as a PiP (picture in picture) or similar? Required references to the licence can be added as a text panel at the end / start. It seems silly to reinvent the wheel for small details.
? Where do I pose technical questions? I am a Mac user and need to convert .mov documents to .ogg.

Please reevaluate and state if the model in the current form can be added to article space. Alternatively please specify any additional improvements required. I am not a biologist / geneticist but a humble IT geometer, so thank you for any help relating to scientific details.
--Cookatoo.ergo.ZooM (talk) 15:23, 6 July 2019 (UTC)

Another video for comparison: [4] DroneB (talk) 23:49, 6 July 2019 (UTC)

"Is it permissible to include an existing WP image": Yes this is normally possible. If the original is under a free license, it will allow derivatives, and so you can include it in a movie.

"Where do I pose technical questions" There is also the computing reference desk. To do the conversion you suggest, perhaps ffmpeg can do that. (ffmpeg -i x.mov x.ogg) Graeme Bartlett (talk) 22:24, 10 July 2019 (UTC)

The huge rotating ATCG letters at the start don't have any explanatory value. There is too much DNA in view. Colors seem to be assigned merely decoratively. Branches disappear and reappear, which seems unreal. We never see the final pair of strands which is the point of the exercise. I would like the two directionalities explained pictorially. Leonardo's Vitruvian Man in the background is unhelpful. DroneB (talk) 15:17, 11 July 2019 (UTC)

What is "Toiposomerase"?--Quisqualis (talk) 20:58, 12 July 2019 (UTC)

Misspelling of Topoisomerase. DroneB (talk) 00:59, 13 July 2019 (UTC)

Compounds and radioactive decay

Imagine that radioactive atoms react with stable atoms and form ionic bonds. When the radioactive atoms decay, what will happen to the compound? A good example is radium chloride, but I don't see anything there about what happens to the chlorine when the radium becomes radon (maybe it's freed, since RaCl2 "was also used in medicine to produce radon gas which in turn was used as a cancer treatment"?), and I couldn't find anything relevant in ionic bond or radioactive decay. Nyttend (talk) 20:53, 6 July 2019 (UTC)

I don't have a full answer to your question as asked and no time now to look further, but doi:10.1126/science.250.4979.392 is on this topic and might be a place to start chasing refs. DMacks (talk) 02:59, 7 July 2019 (UTC)

Many times the compound will be disrupted. If an alpha particle is emitted, the remaining atom will have two extra electrons. Rn²⁻Cl₂ would be very unstable and it is very likely the chlorine will take the electrons and move away. For atoms that undergo beta decay, the nucleus becomes more positive, and electrons remain the same, so a temporary molecule may result. Eg a tritium molecule decaying, will first form the helium hydride ion, as the recoil of the nucleus from the decay is not enough to break the chemical bond. T₂ → HeT⁺. Though most beta decays are much more energetic and could seriously damage the compound.Graeme Bartlett (talk) 05:20, 7 July 2019 (UTC)

You mean all the time. Radioactive decay comes with liberation of much more energy than a chemical bond can withstand: decay energy can be anywhere between a few keV to MeV, while chemical bond are just a few eV (for ref: Electronvolt#Energy_comparisons) (ionic bonding is a special case of chemical bonding) . Even the weakest decay will inject in the compound hundred of time to much energy, and will blow it apart. Gem fr (talk) 13:36, 7 July 2019 (UTC)

While you are correct about the total energy of decay, you are not correct that this energy always stays at the site of decay. Did you forget that decay involves ejection of particles or rays, which can carry away significant amounts of energy? Our decay technique article (the topic of the lead ref I noted) notes as a general pattern that the beta decay of tritium in a tritiated organic structure leaves the helium atom in the structure with only 1.6 eV (not keV or MeV). And that same article of ours also notes the same thing that Graeme Bartlett did: that the remaining energy is not enough to break the helium–tritium bond, but is instead a synehtically useful way of making that convalent structure by tritium decay. DMacks (talk) 15:42, 7 July 2019 (UTC)

You are right, the energy will not stay at the site of decay, most of it will go with the lighter particle emitted. Still, 1.6 eV is too much for a chemical bond, and I think you misread the article, which says that The bond between the carbon atom and the helium-3 ion ... is broken by the recoil. The helium atom almost always leaves as a neutral 3He. Well, I admit that all the time was an overstatement, but, still... (BTW thanks, I didn't knew this decay technique, which I find smart, although of limited practicality) Gem fr (talk) 16:25, 7 July 2019 (UTC)

Exactly...there is still remaining energy that is high enough to break many types of covalent bonds, just not all. He–Li, He–Be, and He-Be are expected to survive from tritium decay. And other elements can also decay to give stable products, such as in the first sucessful synthesis of perbromate (beta-decay of selenate). I'm updating our decay technique article, and it should probably be renamed but I'm not sure to what. DMacks (talk) 20:31, 7 July 2019 (UTC)

Well, I stand corrected. I am still doubtful that the survival is the normal case, but I totally lack expertise and ref to support this view so I back down. I see no problem with the current name of the article; it could use a (chemistry) tag in the title if there were a decay technique in other field that we mentioned in WP, but this is not the case, so... Gem fr (talk) 22:17, 7 July 2019 (UTC)

Surprisingly, the very similar radium fluoride RaF₂ really can become RnF₂ when the radium alpha decays (10.1524/ract.1983.32.13.163). This sort of thing has been used to reduce the amount of Rn emitted by targets when they are irradiated. RnF₂ has a low volatility and is probably an ionic compound(!): Radon#Chemical properties has more information about Rn chemistry. Double sharp (talk) 07:53, 10 July 2019 (UTC)