hypervalent_iodine

Cap'n will know more about this, but I'm pretty sure the ability to edit in BBcode is no longer supported as of the new upgrade. I have no idea why they decided to do this.

Yes, my apologies. I have since realised that being able to edit in HTML is one of my admin super powers, so you won't have all of the buttons that I do. Is there any reason you need to?

There should be a source button on the top left.

In micro, I think you can easily get away with never seeing an organ. I guess it depends exactly where you go with it. I am unsure what is meant by this though: Could you clarify? In any case, I am not sure of ways to get over it per say. I would advise that if you can't, then maybe there is something else you are interested in? Genetics perhaps? Or biochemistry? You probably won't really know until you start getting into it in college anyway, and in actual research settings. Keep your mind open to other possibilities.

What equations do you know of involving moles and concentration? Hint: look at the units.

Not really what I was getting at. Or, it sort of is but I don't think you've fully realised it. Recrystallisation uses, mainly, differences in solubility in various solvents at various temperatures in order to purify a substance. At high temperatures, you want your compound to be (ideally) fully dissolved. Insoluble impurities can then be filtered off. At low temperatures, you want your compound to crash out of solution, leaving behind soluble impurities. Now, this does not mean that all of your compound will crash out. That depends entirely on the solvent, the temperature, volume, and solubility of the compound. Solubility is not an all or nothing phenomena. Your compound might have a solubility of 100 g / L at a certain temperature, which means that at most, you will only get 100 g dissolved in one litre. If you put 150 g of the same compound in one litre, you will have 50 g of solid and 100 g dissolved. If you put 200 g of compound into one litre, you have 100 g of solid, but still only 100 g dissolved. The amount dissolved won't increase unless you increase the temperature or volume. All of which is to say, the reason you always lose 20% of the original mass every time you recrystallise as per the given question is due to solubility. For simplicity, let's pretend that your compound (assume 100 g for the first recrystallising) has a solubility of 120 g / 100 mL at high temperatures, which means when you heat it during recryst with 100 mL it will all dissolve. At the low temperature, let's say it has a solubility of 20 g / 100 mL. So when you cool it, 80 g will crash out and 20 g stays dissolved. When you put the 80 g back through a second recrystallisation, the solubility doesn't change, so when you cool it down, you still have 20 g left dissolved in solution. Do you get what I'm saying? I realise that this might be a bit confusing when you also incorporate the impurity stuff they talk about, but I believe all they really want you to identify is the fact that your compound / mixture is still partly soluble in the cooled solution, hence you lose roughly the same amount every time you do it.

I am asking you what mass you lose every time the recryst is performed. They state the first one is 80% recovery of the original mass, so that's a loss of 20%. The second gave 60% of the original mass, so that's another loss of 20% (80-60 = 20). The final recryst is the same story. You started with 60% of your original mass, and end up with 40%, so that's another loss of 20%. Why do you think that the amount lost is the same, when the amount put in is not? Again, the amount of solvent used is assumed to be identical throughout. Oh, and you didn't answer my other question. What property are you primarily exploiting when performing recrystallisation?

Not really. Did you have a go at answering the questions I asked in my previous post?

Where was water mentioned anywhere in the OP? Think about the masses you are obtaining each time. How much is being lost in the first, second, and third recrystallisation (assuming an original mass of 100 g)? Is it the same loss each time, or different? Why? Hint: you should assume that the volume of solvent used for the recryst is the same each time. You will also want to think about how recrystallisation works - specifically which property you are exploiting when you perform it.

Sorry, just saw your reply. Why Henderson-Hasselbalch? This isn't a buffer question. I don't really follow what you are saying, anyway. The pKa of cyclohexanol is 17. This means that below a pH of 17, it remains mostly in the acid form (HA). Above pH 17, the majority of it will be deprotonated to the conjugate base (A-). Valproic acid has a pKa of 4.8. Similarly, this means that below pH 4.8 the compound remains mostly intact as HA, and above that pH it is mostly deprotonated to the conjugate base. From this we would say that valproic acid is vastly more acidic (i.e. More willing to give up H+) than cyclohexanol is. Why this is comes down to the conjugate bases and their relative stabilities. Do you think the conjugate base of valproic acid is more stable or less stable than the one you drew for cyclohexanol? Why? What is different about their structures that would lead to this?

That's a tough one. Without any other information, I would have put them at about the same pKa. Indeed, looking it up, their pKa's are remarkably similar. If I were to guess, I would say that the 2-chloro substituent of compound 1 helps stabilise the conjugate base through inductive effects moreso than the phenyl ring does in compound 3. That is really what it comes down to with acidity. The more stable the conjugate base, the more favoured the dissociation is, meaning more H+ in solution and higher acidity.

Actually, if you look at the ratio relative intensities of the M peak : M-F peak of the 3-fluoro compared to the 4- and 5-fluoro, you'll see it decreases in both cases. It doesn't decrease by as much in the 4-fluoro, but it does drop. Given that, the trend becomes fairly obvious. Fragmentation drops as you get further away from the nitrogen, so one might assume that this is because the fragmentation isn't as favoured (probably due to stability of the fragment ion). I am curious as to why you are bothering to research into it though? It seems like quite a minor and tedious detail, though I am of course not familiar with what you are doing. 19F NMR seems like it would be more informative if the purpose is to distinguish between the three, if you have the facilities to do it.

Perhaps think about why other iron compounds, or iron itself, does react with acid. What happens to the iron?

What do you think?

Ah, fair enough. I didn't realise it started that young there.

I don't believe 11 years old is high school age. Personally, I would be wary of allowing primary school students to handle sulphuric acid, though (as you note) it should be perfectly safe if performed correctly. Yes, in my opinion gloves probably should have been worn as an extra precaution, however it doesn't sound as though it was overly dangerous. How big was the bottle she was pouring from?

What are your attempts at answering this?

! Moderator Note This is closed. Anonymous Participant, your comments here regarding sexual orientation are absolutely unacceptable. Please review the forum rules before you post next time, (though the way this is going, 'next time' may never come).

! Moderator Note That is good. As we are not a forum for dispensing medical advice, this is closed.

Well, look at its pKa. What is it telling you? Think about it in terms of the stability of the conjugate base. Compare it to a carboxylic acid or something like phenol.

Think about the functional groups and their pKa's.

I was about to post the same photo. I believe it is the same event the OP is talking about. Well, it wouldn't be much of a convention if there were only two people there.

! Moderator Note I think we're done here too.

! Moderator Note Thread closed. Anonymous Participant, if you wish to continue participating, you had best start using the forum in accordance with the rules you agreed to upon signing up. If you have no desire to participate in genuine discussion, you may wish to try your luck elsewhere.

If you click on, "See My Activity" on your profile (to the right of your avatar), then select, 'Posts,' you should see all of your content. I located one post on July 4th 2016 from you (on about page 11):