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[*] posted on 25-9-2022 at 15:50
Symbol for hexavalent uranium?


Why is hexavanet chromium written as Cr6+ and tetravalent uranium is U4+ but hexavalent uranium is always written as UO2 2+? Is this to imply that hexavalent U always has at least two O? Ive spent a lot more time studying compounds and reactions than the fundamentals behind it so I am trying to catch up there.



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[*] posted on 25-9-2022 at 17:03


You are conflating two different things here.

The first is ionic charge. This is written with a superscript. To my knowledge, Cr6+ does not exist.

The second is the oxidation state. This is written with roman numerals. So, Cr(VI) or U(VI) (Or, confusingly, V(V). Notation can be a dog sometimes.)
Oxidation state is an account-keeping device that refers to the number of electrons lost or gained or partially lost or partially gained. Thus, if I have a U(V) compound and I wish to synthesise a U(VI) compound, I know I need an oxidant to do the job. And one electron will be moved for each uranium atom in my synthesis.

For simple monatomic ions the two are the same thing. Cu(II) refers to the existence of Cu2+ ions. But this simplistic approach does not always apply. This is where your confusion arises. When different atoms are bonded together, such as in a polyatomic ion, then the ionic charge will be different from the oxidation state.

In a species such as [UO2]2+, this refers to a polyatomic ion comprised of a uranium atom and two oxygens with an overall charge of +2. Breaking it down we find that the uranium is in the +6 oxidation state: U(VI). We can reconcile these two statements by considering that the oxygens are in the -2 oxidation state. Adding together, +6 plus -2 plus -2 gives an overall charge of +2 for the ion.

It is worth mentioning that these oxidation states or oxidation numbers do not correspond to any physical reality. They are simply an account-keeping device and are useful for tracking the movement of electrons. It is a useful concept but does not tell the whole story. For example, we know that ozone, O3, is an allotrope of oxygen with more oxidising potential than O2. However, both have the same oxidation number of 0.

It is always possible to find exceptions. The answer to your question is that Cr(VI) is not written as Cr6+. Chromium in the +6 oxidation state may be one of a number of different species:
CrO3
[CrO4]2-
[Cr2O7]2-
CrO2Cl2

Similarly, uranium in the +6 oxidation state may be one of a number of different species. the uranyl ion, [UO2]2+ is the only one that I am familiar with.


This segues into a potential concern.
You seem to be interested in processing uranium minerals. Uranium is a complex beast. As well as radioactive and toxic. Its oxidation chemistry is very involved since it has such a large number of possible oxidation states and a very large number of coordination complexes possible. It would be easy to lose track of where your uranium is and what form it is in. This is potentially quite dangerous.
I recommend learning a lot more about oxidation states and complexes before embarking on anything significant with uranium. Why not do an intermediate project to build your knowledge and skills before playing with heavy metals. You could for example begin with pottery grade Cr2O3 and attempt to purify and synthesise a range of chromium compounds: Cr2(SO4)3, (NH4)2Cr2O7 etc. Or, for a bigger challenge, do the same kind of thing with iron. (Fe has so many different oxides and hydroxides and associated water complexes that all look like crud. It is going to be quite similar to processing uranium ore in that regard.)
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[*] posted on 25-9-2022 at 17:41


Thanks for the detailed response. I thought it had to do with the -4 of the O2 but just didn't understand why it's not just written as U6+ most of the time. I have seen it as U(VI) but rarely.

Like I said, I have studied the chemicals and reactions a lot and I understand the results of mixing ionic compounds like UO2 + HNO3 = UO2(NO3)2 but I have lagged behind on the theory of why things react the way they do.

I came across U ore while vacationing in UT by random chance and ever since I have been pretty obsessed and it has been the main driving force of why I love chemistry. Energetics has also played a big part there. I do plan on refining other ores that I have found in abandoned mines and I want to make displays of cool chemicals like vano does but nothing is cooler than radioactive stuff to me lol.




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[*] posted on 25-9-2022 at 17:57


One of the many cool aspects of uranium is that the complexities of it's compounds varies from extremely simple to insanely complex and reaching that realm of extremity is what motivates me to try to understand everything I am doing and desire to do. UF6 is definitely on the list of aspirations but I know my understand is far too behind to attempt such a synthesis. It's been a difficult but fun and rewarding journey having to learn so much without any formal chemistry education.

[Edited on 9-26-2022 by Gammatron]




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[*] posted on 25-9-2022 at 18:26


I hear you.
The problem with embarking on ambitious projects right at the edge of your knowledge is that you do not know the things you don't know. Thus you can be exposed to risky situations without realising it. Even if you are competent and careful. (Think of the Curies.)

I counsel you to go cautiously. Follow tested procedures and go small scale as much as possible. (This is coming from someone who filled his left hand with glass shrapnel because he was being careful with stoichiometry and overlooked something that should have been obvious.)

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[*] posted on 25-9-2022 at 19:04


You are exactly right and I have experienced that many times but when I come to a point where I lack understanding I stop what I'm doing and study it relentlessly until I feel that I know enough to continue. For example, I obtained some tributyl phosphate which is exceptionally good at extracting U from pretty much every other metal so for 3 days I just read patents and old research documents until I understood the process. I ran into some issues and studied more and I solved them.

I'm definitely not trying to discredit your advice and I really appreciate it. I usually do small test tube reactions before moving up, mainly due to experiences of wasting chemicals trying large scale reactions that ended up failing.




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[*] posted on 25-9-2022 at 19:34


These symbols like Cu2+, Cr3+, Al3+ etc. are just very simplified. For example Cu2+ in aqueous solution is mostly in the form of [Cu(H2O)6]2+. But it is very usuful when you try to simply explain some reaction. For example, instead of writing [Cu(H2O)6]2+ + Zn --> Cu + [Zn(H2O)6]2+, you can write simplified reaction Cu2+ + Zn --> Cu + Zn2+. There are some simple ions like Na+, Ca2+, Cl-, (SO4)2- etc however. (UO2)2+ isn't acutally proper composition of ion, it is actually [UO2(H2O)4]2+ (in noncomplexing environment of course). But it is usually written as (UO2)2+, because it is shorter and obvious what ion we are talking about.

Quote: Originally posted by j_sum1  
Similarly, uranium in the +6 oxidation state may be one of a number of different species. the uranyl ion, [UO2]2+ is the only one that I am familiar with.


(UO4)2-, (U2O7)2-, [UF7]-, [UF8]2-. Most other ions are just derivatives of [UO2(H2O)4]2+ where water molecules are displaced by something else.
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[*] posted on 25-9-2022 at 20:24


Very well put, thank you both for your responses! Makes more sense now



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[*] posted on 25-9-2022 at 23:13


If you are fascinated by intricate complexities, then consider playing with vanadium. Youi can buy V2O5 (at different levels of purity, pottery grade is cheapest, but also may contain other stuff, but usually still is better than 95% purity). It has four differnt oxidation states in aqueous chemistry (+2 to +5), and in the +5 oxidation state it has an amazingly complex chemistry, allowing many different kinds of polymetallic cations and anions.

https://woelen.homescience.net/science/chem/solutions/v.html

Try to isolate blue vanadium(IV) compounds, or vanadium(V) compounds, ranging from colorless to bright orange or brick red. I myself even isolated peroxo compounds of vanadium(V), which are quite energetic.
Vanadium is fairly toxic, but not nearly so as uranium, and it is not radioactive. Besides that, vanadium pentoxide can easily be obtained on eBay and at pottery suppliers for a decent price.




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[*] posted on 26-9-2022 at 01:20


Uranium is one of the most chemically studied elements. But also it is the most accessible member of the actinides series. The chemistry of actinides is quite different from other elements because they have accessible and chemically active f-shell (which is not the case in lanthanides).
So, if you compare the first row of transition metals, the second and third row, and the actinides (uranium) you will experience increasing complexity of chemical bonds.
But the point is that number of publications about Uranium is far superior to the number of publications about, let's say, tungsten or some other transition metals in the 2nd and 3rd row. I would say that the tungsten (really very rich) family of complexes is understudied because people invested the most money in studying uranium and plutonium due to their usage in nuclear weapon production.
So, yes, it is the most chemically interesting (somehow) accessible metal but at the same time the metal with the biggest budget for its study, so the chances to find something which didn't get enough attention in the past probably is close to zero.
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[*] posted on 26-9-2022 at 05:57


Actually I have had a small interest in vanadium long before I ever found uranium because of its use as a catalyst in the contact process for making H2SO4. It also turns out that the mines where I got it from contain a lot of V but after all the processing I've done I'm sure it's ended up as waste somewhere. I recall hearing that it is extracted with U in carbonate leach which my preferred method so next time I get more ore I do plan on recovering it.

Is it realistic for any home chemist to expect to discover anything new? I like uranium simply because it is cool and the very fact that it is radioactive makes it a whole lot more interesting to me. It is because of the huge amount of studies and information available that I am able to work with it without a complete understanding of why the reactions work but also drives me to keep learning more.




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[*] posted on 26-9-2022 at 07:00


Quote: Originally posted by Gammatron  

Is it realistic for any home chemist to expect to discover anything new?


Our civilization generated so huge amount of knowledge some part of which is already almost forgotten that for an amateur discovering something new or discovering something forgotten are things that are equally valuable.

In the present time, the motivation and equipment of a professional scientist and an amateur are different. But who has a better potential for discovery?
Surprisingly, it is not always a question of equipment or funding. A man with a modest lab but with good knowledge and understanding of chemistry and with strong motivation is still able to make great discoveries. This is my opinion based on my study of the history of chemistry in the last century. Around mid of 1970s the chemical science represented by a global scientific community lost interest in many topics. Those topics of the research of the past are in a suspended state and have no new publications. The main focus of chemistry after 1970-1980 is doing something which can be used practically - new materials, semiconductors, medicine, etc. Also, many things are not public anymore.
So, this change supposes that the old science of pre-1970s chemistry can have its own continuation. On a question like "how to grow the most beautiful type of malachite crystals," you will unable to find an answer except in old books.
If you would check the great works of chemists of the past you can be surprised by their achievements. And they didn't have in their labs something you cannot make or buy today.

So, yes, it is possible, the point is the knowledge and understanding of chemistry and developing your own way/interest which you can do only making experiments.
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[*] posted on 26-9-2022 at 08:21


I have great time to rediscover molybdenum and tugsten chemistry. There is just little info online about them (unless you know what to look for). Molybdenum have very colorful chemistry (most colorful element in my opinion). You can work with 4 oxidation states in aqueous solution, you need just few simple chemicals. Tungsten is also very interesting. There is so little information about its redox chemistry, which even cotradicts with my observations that I just guess what's going on here.
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[*] posted on 26-9-2022 at 08:43


Bedlasky,

the last more-or-less complete review of the coordination chemistry of tungsten which I found is in the volume 28 of "Progress in Inorganic Chemistry" published in 1981. I am unaware about more recent publications which put light on what we achieved here in the last 40 years in a complete or systematic way. If you know please point me to those publications.



[Edited on 26-9-2022 by teodor]
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[*] posted on 26-9-2022 at 13:09


Everything I know about tungsten redox chemistry comes from two sources. First is brief mention in Remy's inorganic chemistry (old german chemistry book, I have czech edition of it) about reducing tungstate with zinc in HCl/oxalic acid solution to form dark blue W(V) oxalato and chloro complexes and reduction of tungstate solution in hot conc. HCl by zinc to W(IV) and W(III) (I used aluminium foil, because it reacts slower with HCl than zinc powder, so it is lot safer). Second very useful source is polarography of tungstate in HCl.

https://sci-hub.se/https://pubs.acs.org/doi/pdf/10.1021/ja01...

Very useful in terms of understanding reduction of tungstate, but colorchange observed by author very differs with my personal observation. From behavior of reduced species I assume that I formed W(III), W(IV) and probably W(III)/W(IV) mixed species, but I cannot be 100% sure.
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[*] posted on 26-9-2022 at 14:59


Teodor you make a good point about discovering what's been forgotten. I definitely believe that is a fulfilling aspect of hobby chemistry but at the same time for me, creating things that are new to myself even if they are widely publicized is nearly as enjoyable.

Where I fall short in chemistry is being able to create new compounds without studying how someone else did it. For instance if I wanted to make WF6, I wouldn't even know where to begin except for adding HF to W and seeing if anything happens. If not for being able to look up on Google then I wouldn't know that I need to start with WCl6 or WO3. This is where I am trying to get better in chemistry but since I teach myself everything it's hard to understand all that there is to take in. As much as I would like to go to school for it, it's not really an option. I am definitely thankful for this website and everyone's willingness to help though!




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[*] posted on 27-9-2022 at 04:12


If you really want to proceed beyond the level of following other's recipes try to understand at least the following basic concepts:
- stoichiometry
- acid/base reactions
- redox reactions
- tools: balancing equations, the concepts of oxidation number, and formal charge

More advanced subjects are types of bonds, orbitals, coordination chemistry.

For me, doing home chemistry has become much more rewarding when I understood the concepts behind it. It really is fascinating to see these concepts in action, and to understand certain reactions, or even being able to predict certain reactions. Speculation then becomes well-educated guessing, or even predicting. Experiments then can confirm (or reject) your predictions. Also observing things, which cannot be easily explained then becomes much more interesting. Some obervations then lead to deeper discoveries, which go beyond the usual textbook chemistry.

A very nice personal example was this one: https://woelen.homescience.net/science/chem/riddles/iodide+s...

It is not wel-known and no modern textbook mentions this reaction. It is one of those forgotten things.




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[*] posted on 27-9-2022 at 05:33


Grammatron,

I also personally think that the real involvement in amateur chemistry doesn't start with discovering something new or forgotten but with your interest in basic forces of nature and the feeling of some personal involvement when you do some experiments.
It doesn't matter how many people did this experiment, every observer is able to do his own personal observation.
There is no such thing as "well-known reactions". When we think we understand something usually what we think about is only some miracle. Seeing more in very simple things is the way to go through amateur chemistry if you ask me.

Except for the danger and over-complexity involved in getting WF6 your way of thinking is right.
But chemistry is the science that opposes any proud human mind. Only through careful observation of how things really proceed, building and destroying theories, and a respectful attitude to the work of other people, especially proven methods of getting compounds and observations we can really enjoy this science.

It is quite normal that for the things like getting WF6 or whatever you always start with a literature search. Don't expect Google to provide a good service for amateur chemists. Ironically, the top-quality links usually point back to this forum.

But there are also good old books which still contain the most information for us. Most of them are in electronic form somewhere but not all of them yet. I can recommend this order of search if the question is how to make some inorganic compounds:

- The "Inorganic syntheses" series. It is published every year starting from 1939 and contains newly discovered and working methods of preparation of inorganic compounds; (e.g. WF6 is covered there).
- Sciencemadness wiki/forum
- youtube videos
- A set of very quality receipts from the books of Brauer, Dodd and Robinson, Henderson and Fernelius, Walton, and some others (several of such books are in the SM library and could be found by the keyword "inorganic")
- Gmelin handbook. There are no complete scans but some volumes are available through sci-hub.se.
- Google
- Nothing works - ask in this forum (but you can do it at any step of course).

As for the book with good coverage of halides and their preparation (WF6, WCl6 are in this class) I can recommend Colton and Canterford "Halides of the first row transition metals" and "Halides of the second and third row transition metals". If you will find a method not covered there it is a good chance that your publication on SM of your method will gather good attention.
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[*] posted on 27-9-2022 at 12:25


I know how to use stoichiomtry and molarity and doing displacement reactions and I have a basic understanding of oxidation states which i am still learning but redox, orbitals and coordination chem are things I haven't learned much about.

Who would've guessed that such a simple reaction would be so unknown. It is an amazing feeling to rediscover things that have been lost but like I said, even discovering things that are well known but new to yourself is almost as good. It is what always keeps me interested in chemistry.

Thanks teodor for the suggestions on books, I have a website saved on my computer where you can download copies of educational books for free so I will look for those and also post a link to the site.

Google is usually good enough, especially if I can find an example of someone performing the reaction but most of the stuff involving uranium I have found as patents and old declassified documents which just gives general outlines for the processes. This has actually turned out to be a good thing for me cause it forced me to learn about moles and balancing equations in order to proceed with experiments I wanted to do. For the same reason I have had to learn about oxidation states because most U compounds have to be +6 to go into solution. I have so much more to learn though which is why I asked the original question.





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[*] posted on 28-9-2022 at 01:39


Quote: Originally posted by woelen  
If you really want to proceed beyond the level of following other's recipes try to understand at least the following basic concepts:
- stoichiometry
- acid/base reactions
- redox reactions
- tools: balancing equations, the concepts of oxidation number, and formal charge

More advanced subjects are types of bonds, orbitals, coordination chemistry.

Do you feel you should also understand the concepts of:
- explosives
- sensitivity
- miscibility/solubility
- nature of poisons and corrosive substances
- easy to neutralize/hard to neutralize poisons
- good warning properties/foul smell/immediate irritation vs. delayed or accumulative toxicity?
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[*] posted on 28-9-2022 at 02:37


The things you mention are of another level. What I mention are more scientific/teoretical concepts, which can be used to understand what happens in practical situations. What you mention is a practical continuation of underlying theoretical concepts.

E.g. the theory of explosives builds on theories about energy, involved in reactions (exotherm vs. endotherm), and theories about kinetics (mechanism and speed of reactions). Sensitivity also builds on kinetics (path of reaction, low activation energy needed or not). The same is true about the other things.

Your things have great value in practical work, knowledge about these can be very useful in assessing risks, being able to recognize dangerous things, and to act accordingly. But having only understanding of these things, without understanding of the more theoretical underlying concepts, will reduce chemistry to little more than having so-called 'point-knowledge'. Knowing a lot of a specific reaction, a specific compound, how it behaves in practice, etc., but not being able to generalize things, to extrapolate into the unknown. With just these things, you have to learn many things by heart, with the underlying concepts having in your tool set as well, you can connect things, make remembering of things easier, and sometimes you even can derive things.

An example I have for myself is the use of so-called half-reactions in aqueous redox chemistry. Many people try to memorize reactions like Cr2O7(2-) + 14H(+) + 6e --> 2 Cr(3+) + 7H2O, and similar reactions for manganese, vanadium, iron, certain organic compounds, and many more. If you understand the underlying concepts, then you only need to memorize the main starting product and end product (in this example Cr2O7(2-) and Cr(3+)) and then you just generate the reaction and you also can see easily whether it needs acid, base, or not any acid/base at all. I myself even wrote a computer program, which can generate this kind of half-reactions for you (and do a lot of other things):

https://woelen.homescience.net/chemeq/tutor/tutor.html?
https://woelen.homescience.net/chemeq




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[*] posted on 28-9-2022 at 04:39


Quote: Originally posted by woelen  
The things you mention are of another level. What I mention are more scientific/teoretical concepts, which can be used to understand what happens in practical situations. What you mention is a practical continuation of underlying theoretical concepts.

E.g. the theory of explosives builds on theories about energy, involved in reactions (exotherm vs. endotherm), and theories about kinetics (mechanism and speed of reactions). Sensitivity also builds on kinetics (path of reaction, low activation energy needed or not). The same is true about the other things.

Your things have great value in practical work, knowledge about these can be very useful in assessing risks, being able to recognize dangerous things, and to act accordingly. But having only understanding of these things, without understanding of the more theoretical underlying concepts, will reduce chemistry to little more than having so-called 'point-knowledge'. Knowing a lot of a specific reaction, a specific compound, how it behaves in practice, etc., but not being able to generalize things, to extrapolate into the unknown. With just these things, you have to learn many things by heart, with the underlying concepts having in your tool set as well, you can connect things, make remembering of things easier, and sometimes you even can derive things.

But that´s why you need the theoretical concepts to go beyond the level of following established recipes. To predict likely consequences - like, something between your target product, your reagents or likely side products exploding, corroding leaks through your apparatus, or getting out and not giving adequate warning via colour/smell/irritation before doing harm.
WF6?
It is not explosive. (Hardly any fluorides are).
But a lot of fluorides are poisonous. Better ask what aren´t.
The bigger part of safe fluorides are the ionic solids that are refractory and hard to dissolve or evaporate. CaF2 and many other metal fluorides. For transition metals it tends to be the lower fluorides that are refractory solids. WF6 boils at +17 Celsius. It is not one of these refractory solids.
And the other group of safe fluorides is the covalent molecules which are so tightly bonded that neither water nor biochemistry manages to attack them. Basically two simple ones. CF4 and SF6. And bunch of fluoroalkane derivatives. But nothing beyond it. Neither NF3 nor SeF6 is inert enough to be nontoxic. And WF6 is known to be readily hydrolyzed. Therefore, we can assure that WF6 is a toxic gas - and the handling methods should be chosen accordingly.

[Edited on 28-9-2022 by chornedsnorkack]
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[*] posted on 28-9-2022 at 05:57


Your reasoning is perfectly valid, but if you look at the process of your reasoning, then you also see that you use a lot of underlying concepts to make this possible. You use concepts of hydrolysis, reactivity, types of bonding. From these concepts you are capable of figuring out that WF6 must almost certainly be a toxic compound, even though you never did anything before with WF6.

Interesting thing of this is that we are reasoning at meta-level. Not about WF6 and its dangers, but about the process of thinking about WF6 and its dangers ;)




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[*] posted on 28-9-2022 at 11:50


Quote: Originally posted by teodor  
Quote: Originally posted by Gammatron  

Is it realistic for any home chemist to expect to discover anything new?


Our civilization generated so huge amount of knowledge some part of which is already almost forgotten that for an amateur discovering something new or discovering something forgotten are things that are equally valuable.

In the present time, the motivation and equipment of a professional scientist and an amateur are different. But who has a better potential for discovery?
Surprisingly, it is not always a question of equipment or funding. A man with a modest lab but with good knowledge and understanding of chemistry and with strong motivation is still able to make great discoveries. This is my opinion based on my study of the history of chemistry in the last century. Around mid of 1970s the chemical science represented by a global scientific community lost interest in many topics. Those topics of the research of the past are in a suspended state and have no new publications. The main focus of chemistry after 1970-1980 is doing something which can be used practically - new materials, semiconductors, medicine, etc. Also, many things are not public anymore.
So, this change supposes that the old science of pre-1970s chemistry can have its own continuation. On a question like "how to grow the most beautiful type of malachite crystals," you will unable to find an answer except in old books.
If you would check the great works of chemists of the past you can be surprised by their achievements. And they didn't have in their labs something you cannot make or buy today.

So, yes, it is possible, the point is the knowledge and understanding of chemistry and developing your own way/interest which you can do only making experiments.

For example, where would you search for an answer to a question like:

Quote:

In 100 % triflic acid, how many solvent molecules does uranyl triflate crystallize with?

Triflic acid is remarkably convenient reagent if you have it...:
Stronger than sulpuric acid. About as strong as disulphuric or fluorosulphuric acid, but several conveniences compared to either.
Won´t solidify at concentrations above 100%. Sulphuric acid has disulphuric acid at H2S2O7, and nasty SO3 polymers, while triflic anhydride stays liquid at room temperature and boils at 82 Celsius
Fumes less than SO3, but easier to boil off than H2SO4.
Seems to be less oxidizing.
And yet, triflic acid was only discovered in 1954. Properties of obscure triflates won´t be in old books. Even the basics like triflic acid/water azeotrope temperature and composition... searched but could not find it.
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teodor
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[*] posted on 28-9-2022 at 13:41


chornedsnorkack, this is a good example to illustrate woelen's words.

First, the knowledge that some types of salts always crystallize with solvent molecules is the element of the theory of solutions.
To make this particular knowledge about triffic acid useful it should be pointed out to which family of solvents triffic acid belongs (there is a limited number of possible solvent families) and which benefits this acid has as a solvent compared to more available or studied solvents of the same family, e.g. 100% H2SO4. What is the product of dissociation and which compounds represent bases and acids in this solvent.
Based on this information it would be possible to predict (as a hypothesis) some benefits of this solvent over H2SO4 and check it.

So, there is a little point in knowledge if this knowledge is not a part of some system, and there is a little point in an experiment if there is no hypothesis to check.



[Edited on 28-9-2022 by teodor]
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