CCMR - Ask A Scientist!
As part of their educational outreach, the Cornell Center for Materials Research (CCMR) hosts an “Ask a Scientist” column in the local paper, the Ithaca Journal. The columns are archived on the CCMR website.
I’ve now answered two relatively technical science questions posed by high school students while I’ve been at Cornell. The idea is to answer the question in a way that it’s readable by a middle-school student. The CCMR staff keeps a list of submitted questions and looks for grad students, postdocs, faculty at Cornell and other schools near Ithaca who have some expertise in the subject of the question and can answer it.
For example: How accurate is the VSEPR model of molecular geometry for predicting the shapes of large, complex molecules?
I should have mentioned a bit more about the “valence shell electron-pair repulsion” model. I learned it in high school and college and have taught it a few times since then. Like all science models, it didn’t just appear out of thin air.
Some of the ideas were proposed in 1940 by N. V. Sidgwick and H. E. Powell, and further developed by R. S. Nyholm and R. J. Gillespie. In particular, Gillespie worked and revised the model and really pushed the ideas into teaching molecular geometry in many textbooks and courses.
I digress. Any “ask a chemist” questions for the blog?
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Trackback by EphBlog — 3 years, 3 months ago.
Ask a Chemist
Geoff Hutchison ‘99 is answering chemisty questions for the local paper in Ithaca. He offers to answer ours as well. Do you have any questions for Geoff? Here are mine: 1) Is percholate really that dangerous? 2) Are you as…
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Geoff — 3 years, 2 months ago.
David asked about perchorate levels. I am, by no means, an expert on toxicology or environmental impact — so it’s hard for me to speak authoritatively. I suspect a variety of chemists at Williams have also spoken about the relevance of perchlorates to Williamstown.
Perchlorate is a chemical species (a complex anion) used for a variety of chemical reactions, analyses, some fertilizers, but mostly in rocket fuels and explosives. (Perchlorate solids can decompose explosively.) There is some concern about concentrations of perchlorates in food and water — largely because it can interfere with the uptake of iodine into the thyroid. The exact level of concern has been difficult to establish, which is why there are few exposure limits.
(I suspect none of that is particularly news to David, but I felt I should answer his question. He had some other remark, but I suspect it was meant as a rhetorical question and so I will not address it.)
Jennifer Samson — 3 years, 1 month ago.
Was wondering what the activation energy is for a C14 atom to combine with O2? I’m not sure if the isotope distinction makes any difference, but this is in relation to a carbon-dating issue so that is why I mention it. Where could I find this?
Geoff — 3 years, 1 month ago.
Jennifer,
Sorry for the delayed response. I’m assuming you want to know the activation barrier for 14C + O2 => CO2. I haven’t seen any theoretical or experimental data on this, though I did search. There are activation barrier differences for hydrogen vs. deuterium, but there’s probably not a significant energy difference for 14C vs. 12C, since we’re talking about a 16% mass difference (while H vs. D is ~200%).
But if you want an exact difference in activation barrier, it’s not hard to calculate it theoretically. Send me an e-mail if you’d like me to compute an exact number.
Andrew — 2 years, 12 months ago.
Solubility of methyl violet
The methyl violets are aniline dyes which consist basically of three aniline molecules conjugated at the center and with varying degrees of methylation of the amine groups. Structures:
http://en.wikipedia.org/wiki/Methyl_violet
I want to know what is the “theoretically ideal” solvent for these molecules (we don’t necessarily know which of the three configurations it is).
From experimentation I already know that they are soluble in water, in glacial acetic acid, and in ethoxyethanol > ethanol > methanol. However those are just “textbook” examples of common solvents and that information is already widely know. What I am really asking is, given the choice of any solvent or combination of solvents which are liquid(s) at room temperature, what would you choose from the point of view of solubility theory? Would aniline itself be a good choice? Are there some generalizations which can be made about the solubility of the methyl violets looking at the structures and the functional groups ?