hypervalent_iodine

5 hours ago, studiot said:

Since this is coursework, here are some hints.

But since it is important to understand what you are doing, please ask if there is any part you do not understand.

First it is important to understand the definition of solubility product. So ask if you do not.
Solubility products are different from other constants in that they are not a ratio of concentrations.

When a slightly soluble substance goes into solution, leaving some or most of its substance in physical contact with the solution the undissolved doesn not change in quantity.
The solution is saturated according to the normal reaction equation for solution

$Fe{\left( {OH} \right)_3} \Leftrightarrow F{e^{3 + }} + 3{\left( {OH} \right)^ - }$

With an equilibrium constant K_eq given by  (in your case)

${K_{eq}} = \frac{{\left[ {F{e^{3 + }}} \right]{{\left[ {O{H^ - }} \right]}^3}}}{{\left[ {Fe{{\left( {OH} \right)}_3}} \right]}}$

The bottom part is the amount of the substance that has gone into solution.

The concentration of this is therefore the concentration of the ferric hydroxide that is in solution that you are given as 4 x 10^-10M

I have circled this value in pink.

 

So to move on we multiply both sides of this equation by the concentration of the ferric hydroxide to get the solubility product, K_sp.

${K_{sp}} = \left[ {Fe{{\left( {OH} \right)}_3}} \right]{K_{eq}} = \left[ {F{e^{3 + }}} \right]{\left[ {O{H^ - }} \right]^3}$

Substituting values and forming the other equations of equilibrium should enable you to complete this question.

Come back and let us know how you get on.

 

 

 

 

I can see what you’re maybe getting at here, but it is confusing. The Keq would not be written like that as the equilibrium is not dependant on the concentration of the solid salt. The expression for Ksp is not actually different from how you would write other equilibrium expressions, since you typically don’t include terms for solid or liquid components in any expression for Keq. This is the same in, for example, expressions for Ka, where water is not included. The reasoning is that these components are normally in such large amounts relative to other components, that minor changes to their concentration has no effect on the overall equilibrium. This holds true for Ksp since we assume at a minimum that the solution is at saturation point; adding more salt has no effect on the concentration of ions in solution, and therefore no effect on the equilibrium. 

19 hours ago, mdk2 said:

If that is the case, then how can we assume that the concentration of Fe³⁺ is equal to the concentration of Fe(OH)₃ at saturation? 

The answer to this is simply stoichiometry. If x number of moles of a salt has dissolved, and the ratio of it to one of its ions is 1:1, then x number of moles of that ion is in solution. Note of course that this concentration is not the same as the amount of salt that might have been added to solution, just how much at equilibrium is actually in solution. I think you understand most of the concepts here, so I don’t think you’re necessarily missing anything. Ksp and molar solubility are closely linked - if one is low, so is the other. We might use the numbers for different things or to work out other problems. Practically, molar solubility is a more useful and easily relatable number if you just want to know how soluble something is. However, if you want to know the ion concentration in more complicated scenarios (I’m talking common ion effect) or if you want to say predict whether something will precipitate in complex solutions, you would need to use Ksp. Perhaps have a read of this: https://www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/Solubility_Products.htm

52 minutes ago, CharonY said:

Oh yeah, I think that is the follow-up to a follow-up (the second by Molina study showed no beneficial effects). But critically, the study was more set up like a case or observational study rather than a efficacy test. At this point the data looks inconclusive to me. 

Inconclusive is one way of putting it. Their first paper with was highly suspect and contained a lot of concerning ethical elements. Their follow ups don't seem to add very much, and is at odds with a lot of the other data that has been published regarding HCQ. Derek Lowe's coverage on it has been quite informative: 

https://blogs.sciencemag.org/pipeline/archives/2020/04/16/more-small-molecule-clinical-data-against-covid-19-as-of-april-16

https://blogs.sciencemag.org/pipeline/archives/2020/04/11/the-latest-hydroxychloroquine-data-as-of-april-11

https://blogs.sciencemag.org/pipeline/archives/2020/03/29/more-on-cloroquine-azithromycin-and-on-dr-raoult 

I don't think there has necessarily been any political meddling. They are working with the data that they have, but I also think that this is where the issue potentially lies, since I don't believe there has been significant testing done in children to know what risk they actually pose to other people.  

I completely agree with you on your points about school closures - the long term economic effects would be disastrous. In addition to your points I would also comment that universities, which are already struggling with the loss of international student money, would surely go bust if they also lost an entire graduating year of domestic students.  

18 minutes ago, druS said:

This seems inconsistent with the advice from the Chief Medical Officer in Australia. The view is that the risk of transmission in schools is low and that teachers greatest risk is from other teachers, that parents greatest risk is exposure to other parents during drop off. I understand that schools are a something of a petri dish for many virus, but the view here seems to be that this virus is different.

Or the motivation to keep schools open is different. 

There was a paper circulating a little while ago that caught my attention, published in Nature. 

https://www.nature.com/articles/s41586-020-2223-y

To be honest, I am pretty baffled that it was published in Nature. The top leads identified in their screening assay are known as pan-assay interference compounds (PAINs). IOW, they are nuisance compounds and generally not something you would pursue in a drug design campaign. In fact, the seminal paper that discusses PAINs is a Nature paper (https://www.nature.com/news/chemistry-chemical-con-artists-foil-drug-discovery-1.15991), which makes this even more confusing. I can't imagine anyone with a med chem background would have reviewed this, as the red flags should have been very obvious. In any med chem journal, this paper would have been rejected since you have to screen for PAINs as part of their submission guidelines. I'm worried that this signals a general lowering of the bar when it comes to these sorts of publications, which will only make things more difficult in the long run. Derek Lowe has written some good blog posts on the matter:

https://blogs.sciencemag.org/pipeline/archives/2020/04/10/more-on-screening-for-coronavirus-therapies

6 hours ago, CharonY said:

It is weird, isn't it? Is it only me or are bio papers getting sloppier in the last one or two decades?

I’d certainly believe it. A lot of the students I’ve dealt with over the last 5 years in the micro and genetics labs I’ve worked in don’t seem to realise that there is an inherent ambiguity, because that is just how they’ve always interpreted it. 

farsideofmoon has been suspended for 2 weeks for repeated thread hijacking. 

Biology papers frequently don’t specify, but I believe the assumption is generally w/v.

6 hours ago, Prometheus said:

I meant specifically for recommending research papers to academics in a similar way that youtube videos, or whatever, are recommended (your link doesn't seem to address this, at least in the abstract). I was thinking of something more like this.

A lot of journal websites do this, as does (I think) PubMed. I’m not sure how good it is, but it exists.

13 hours ago, CharonY said:

My work is, unfortunately, somewhat multidisciplinary, so my approach is likely very different from someone who works in a far more specialized area with more focused papers/reviews.

I think my approach with reviews and reading papers largely mirrors yours for the same reasons, although I tend to use SciFinder and Google Scholar rather than PubMed. Usually after the first pass through to filter out obviously irrelevant papers, I download all of the references + abstracts and then read enough of the papers to be able to categorise in EndNote before I move on to reading them more in depth as I write. I can also look up papers related to particular chemical structures or reactions using structure searches, which is very helpful in capturing as much of the literature as possible, although it doesn't always work depending on the topic. 

More broadly, I find that subscribing to certain journal email lists in your field is a good way of keeping an eye on what's happening in the field. I don't always scan every email I get, but I will usually look through the list of online preprints from journals like J. Med. Chem. or J. Org. Chem. and read the papers I think look interesting. Admittedly, unless I really want to know something specific about a protocol, I often skip the methods section. 

Hydrogen bonding requires a polar atom with a lone pair of electrons, such as nitrogen and oxygen, and an electropositive hydrogen in a polar bond, such as -OH hydrogens and -NH hydrogens. So, the ether can't actually H-bond to itself because it doesn't meet the second requirement, but the alcohol and carboxylic acids both can. 

16 hours ago, Questionasker said:

Hi, sorry for the late reply.

Just by looking at what they are, keep in mind that i'm only going to predict the boiling points. I actually have never heard of 'Diethyl ether' and 'Acetic acid' I predict it will go:

* Diethyl ether

* Acetic acid

*Ethanol

* Ethane

 

Not quite. Three of these molecules can undergo hydrogen bonding. One cannot. Since they are close in terms of molecular size, you can rank them roughly by looking at the number of potential hydrogen bonds they can form to other molecules. Acetic acid has two oxygens that can both hydrogen bond, and a polar hydrogen that can form hydrogen bonds. Ethanol has one oxygen and a polar hydrogen, and diethyl ether only has an oxygen. Ethane has nothing that can hydrogen bond. Hence, you might predict that acetic acid would have the highest boiling point, since it has the highest number of potential hydrogen bond sites, followed by ethanol, diethyl ether, and then ethane. 

Firstly, what do you know about the solubility of sodium and other Group I metal compounds? Have you written out the balanced reactions? You don’t need to know what the initial iron compound is for this, just assume you have either Fe 2+ or Fe 3+ ions (as in, write two equations). 

3 hours ago, Questionasker said:

With an alcohol, i believe, intermolecular forces will exist since O-H has both a slightly negative and positive charge. The electrons of the O-H are unevenly distributed since Oxygen has a higher electronegativity than hydrogen, therefore pulling the electron towards it. This will then cause a Dipole dipole effect when there are different charges at opposite end of the alcohol. However, this happens for a very short amount of time since electrons move incredibly fast. So due to the Van der waals effect, the alcohol will have a temporary dipole effect which means that it can bond to other molecules, but I can't imagine that it'll be strong. So going by what I mentioned, If it's correct, the hydrogen should be oscillating between neutral and having a slighy positive charge. This must mean that it can covalently bond the hydrocarbon, such as ethane, to another ethane molecule.

 

 

On average, the OH bond will be polarised. In fact, it can participate in a particular type of dipole interaction called hydrogen bonding. As with all electrostatic interactions, it is not overly strong when you compare it to covalent bond strengths, but hydrogen bonds are considered quite a bit stronger than other intermolecular attractive forces. I have bolded a sentence that is not quite right. You won't covalently bond two ethane molecules together. You will get Van der Waals (also London dispersion forces) between molecules of ethane, but that's about it. They are very weak interactions. You will also get Van der Waals interactions with alcohol molecules. When you compare the two, you have (for example) ethanol, which has hydrogen bonding and Van der Waals interactions, and ethane, which only contains Van der Waals interactions. As you noted above, the stronger the interactions and the more of them that there are, the more energy it requires to break intermolecular bonds and pull molecules apart, which translates to a higher boiling point. As such, you would reasonably expect ethanol to have a higher boiling point to ethane. Another interesting comparison is between diethyl ether, acetic acid, ethanol and ethane. Can you predict the order of boiling points between those molecules from highest to lowest? 

Nitrogen can’t accommodate 5 covalent bonds. It can and does form ammonium salts, with the halogen acting as a counter ion.

Lord, yes, you’re very right and that was a very stupid mistake on my part. Working from home has fried my brain. 
 

To your question, you need to consider that the molecules are all salts. Have you constructed molecular diagrams for the molecules to know how many bonds and lone pairs they have?

Yes, more or less. So with an alcohol, can you identify what sort of intermolecular interactions might exist? Hydrogen bonding, London dispersion, dipole, Van der Waals, etc.? 

Formal charges of the atoms is not the same as the net charge of the molecule. For example, H₂O has a net charge of zero, but the formal charges for the atoms are +1 (hydrogen) and -2 (oxygen). 

As of a few minutes ago, I went ahead and merged many of the threads and posts regarding Coronavirus into three threads:

I understand that many have questions regarding coronavirus / COVID-19, but I think we can do without 20 different threads on the topic. To reduce clutter, I have created the above threads, and would ask members to please direct their questions / findings to the relevant one. If anyone objects or thinks I have missed something, please let me know. I myself am working from home; time is a luxury I have far too much of at the moment.