hypervalent_iodine

A university library would be much more likely to have a text book of that nature than a city library. If you can, go there and have a look. I'm not sure if you can purchase the books in PDF format; a quick look on Amazon suggests you have to purchase the actual book.

Nylon is an organic compound, synthetic polymer though it may be.

Have you considered going to a library?

Do you have any point you would like to discuss or any queries that relate to organic chemistry at all? This seems like it would belong in the genetics subforum to me.

Hal, My point is that presented in post #115. Thank you for the opportunity to rephrase it; however, I feel that it still stands as is.

Apparently, the definition if liquefy and liquefaction depends on where you look, so I am willing to concede this point. In any case, my point from above still stands.

The terms you are attempting to describe already have set definitions, which are very specific in respect to what they encompass. You cannot change these preset definitions or argue them based on personal opinion of what it "should be" or what would be more "convenient". That's all there is to it.

Liquification is exactly what you're describing. Sure, life might be easier if we didn't have to prove that a substance can reversibly turn into a liquid to show that it melts. What it comes down to is scientific rigor and the need to properly justify yourself to be able to claim something as being true. Melting describes a reversible phase change from solid to liquid, so to properly prove that something is melted you should be able to see the reverse phase change as well. This being said, in organic chemistry, unless the compound decomposes at or around its melting temperature, there is generally no need to watch the sample re-solidify (although it's usually quite obvious). What would be easy and convenient would be if we did away with superfluous terms such as "Hal's melting" and just call things what they are; in your case, liquification. No, that would be condensation, not liquification. The latter very strictly defines the process of a solid changing into a liquid whereas the former is the process of a gas changing into a liquid.

Technically hormones elicit these processes via chemical reactions, so I would not say this is entirely correct.

Standardisation of what, exactly?

To be honest, I'm not really experienced with the stuff. According to the wiki page, it's yellow or red, so I guess you're okay.

No problems! (and be careful with the aqua regia)

Could be that the nail was a different composition.

I'm not 100%, but I would think that the nitric acid in the aqua regia is oxidising the iron, which then reacts with HCl to form the iron chloride salt.

It's been a little while since I've had to deal with polymer chemistry, but I'll see if I can help you as best I can. Though I am sure you know this, tacticity is a term that refers to the relative stereochemistry of adjacent chiral centres within a polymer chain. Achieving a defined sequence of chiral centres in a polymer (i.e. with iso- and syndiotactic polymers) requires stereoselective modes of polymerization. PVC, however, is generally made via radical polymerization. This type of mechanism, coupled with the fact that the vinyl chloride monomer is planar, means that there is really nothing that would promote formation of one stereocentre over another. Thus, you get a random sequence of both along the polymer chain. Firstly, a correction. To my knowledge, PVC is an amorphous solid, rather than a semi-crystalline one. I'm not entirely sure what your question is here, but I'll try to explain why PVC is less crystalline that HDPE for you. Crystallinity of polymers comes down to how tightly they pack together. A good analogy to this would be comparing beeswax and olive oil; at room temperature, beeswax is fairly solid whereas olive oil is a liquid. The reason behind this is due to how they pack. Olive oil contains a large portion of fatty acid chains that have cis double bonds in them, such as oleic acid: The result of this is that the fatty acid chains become kinked (as in the diagram) and as such, the fatty acids can't pack in tightly together causing the olive oil to therefore exist as a liquid. Beeswax on the other hand does not contain as many of these and instead consists of more saturated fats (i.e. fatty acids without double bonds), such as palmitic acid: These type of straight chain hydrocarbons are not kinked, unlike in the oleic acid. As such, these fatty acid chains can pack very close to one another, which in turn causes the beeswax to solidify at a lower temperature than olive oil. A long analogy, but the case is very similar when we then talk about crystallinity in that it all comes down to the packing. Consider the following pictures: I used polystyrene as it gives a much clearer and more apparent picture of what I'm trying to say. It should be immediately obvious that the polymer on the right (the isotactic one) will pack a lot tighter and into a lot more of an ordered structure than will the one on the left. Simply, my point is this: a higher degree of structural order and symmetry on a molecular level will lead to a higher degree of crystallinity on a macro level. HDPE contains little to no branch chains and is completely without stereocentres, which means that it will pack much more tightly and much more orderly than PVC, which is atactic. In fact, HDPE is one of the few polymers whose individual chains lie in an almost completely straight line, compared to the spaghetti-like mess you see in other polymers like PVC. The compression strength you mentioned I think would come down to how brittle each polymer is. If you have a look at the stress-strain plots of each of these, I suspect what you'll find is that PVC will undergo what's called 'necking', which refers to the way some polymer materials stretch and deform before they snap (such as in this picture). HDPE on the other hand will act somewhat like glass in the sense that it will withstand a certain amount of pressure before it simply snaps. This has obvious importance in terms of its use as material for pipes, etc. This is a guess though, so perhaps you might want to look into it (or someone else here can correct me). Its high degree of crystallinity is what makes it not as strong as PVC. It's extremely brittle because of how linear it is. PVC, however, is more like a spaghetti matrix; there are polymer chains everywhere and they're all interwoven and just generally being crazy. I don't think that PVC is cross linked simply because mechanistically, it is not likely to happen. I would think it was because of the high crystallinty of HDPE compared to PVC, yes. No. The Tg is a type of phase change that occurs before, but approaches, the melting temperature, Tm. A highly crystalline solid isn't going to melt at a lower temperature than something that's an amorphous solid, now is it? It's the same with the Tg. The spaghetti analogy I keep mentioning is in fact a commonly encountered one for amorphous solids of this type. Like spaghetti, individual polymer strands are flexible and can easily slide over one another. It is not the same for HDPE, which has a more restricted molecular motion, hence the difference. That's ok, sorry for the rather lengthy answers.

Well you could also talk about their reactivities as per the reactivity series. This could easily be discussed in terms of how well potassium is able to lose an electron over lithium, etc. Additionally, you will want to discuss electronegativity - i.e. which one is more electronegative and why that is.

Sounds like aqua regia or possibly nitric acid. Given how quickly it corroded the nail, I'm going with aqua regia.

That's very true, they do form positive ions. However, they do still have a certain degree of electron affinity, albeit small. Are you comfortable with the concept of electronegativity and the trends seen in the periodic table?

Well you've done the hard part for converting to mmol and micromol. All you have to do work out the conversion factor, which a simple Google search will give you. Simply, for every mole you have 1000 mmoles (hence milli) and for every millimole you have 1000 micromol. As an example, 0.02 moles would equate to 20 mmol (0.02 x 1000) and 20000 micromoles (20 x 1000 or 0.02 x 1000000). The second question you need to ask yourself how many moles of urea you are taking out, remembering that that in every litre you have ~ 0.04 moles, and then work out the new concentration using the same process as in question 1. The third question is kind of the reverse of the above, assuming you have 1 litre of your new solutions (2mmol, etc.). For a.), you know you have 2 mmol of urea in every litre of solution. To make this, how many mL of your stock solution will you need, baring in mind that you have 0.04 moles in every litre of stock solution? The fourth question should come easily after the above two, but if you're stuck feel free to ask for help

And that would be correct! Are you okay with the other questions?

If this is for Q1, then no, not quite. You seem to have the calculating your number of moles down, so I'll skip that in the interest of brevity. The best way to figure it out is to look at what units your measurements are in. Molarity is a measure of the number of moles of something you have in a litre of solvent. So for instance, if I have 1 mole of, say, NaCl in 0.5 litres of water then my concentration would be 2M - i.e. 1 mole / 0.5 L. I always used to have trouble remembering which way to divide, but that becomes easy when looking at the units; we know molarity is moles per litre, so therefore to calculate the concentration of a sample we just divide the number of moles by the volume.

Do you know how to work out the molar mass of a compound?

I gave you the SciFinder suggestion because it is the easiest way to get more specific information on brominating similar compounds to yours. It would be advisable for you to learn how to use it as it is a very useful tool for chemists. Most universities and institutions will have a license to it, all you have to do is register an account. I have no idea what level you are, so it is perfectly reasonable that I ask for further clarification on points I am unsure of in your post so that I may better help you. If you didn't want someone to comment on it, then why did you bother writing it? Calling my expertise into question (again) does nothing to get you an answer, as I have already stated. You also have no authority to tell me where I can and cannot post. FYI, just after my first post I went and consulted a colleague with a great deal of experience in NBS bromination reactions in substrates somewhat similar to yours. Unfortunately for you, I don't feel obliged to share the information. He's just a PhD student after all, so what could he possibly know?!

I'm assuming this is a homework question? If so, you'll need to be more specific with exactly what it is that confuses you so that we can help you, rather than simply doing your homework for you.