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 njdevsfn95 11-12-2012 05:24 PM

Chemistry Help Thread - HS, General Chem

If you have any chemistry questions, feel free to ask here.

Organic Chem isnt my thing but i am good at math so i may be helpful for quantitative analysis and potentially quantum (we called it "physical" but quantum sounds much cooler) chemistry questions too.

Of course im not the only chemist on here.

 The Perfect Paradox 11-14-2012 12:25 PM

I would be willing to help out as well. In the process of finishing up Organic Chemistry I this semester.

I'd certainly be willing to help with any Organic Chem and Biochem questions. Phys Chem and Inorganic, not so much. ;)

 PSUCapsFan 11-17-2012 07:08 PM

I can help with O chem and general. Started grad school this fall for organic chemistry.

 KesselBuiltMyHotrod 12-12-2012 02:17 PM

So in my chem class we basically follow the octet rule for Lewis diagrams. I see around the internet a lot of places saying that using formal charge gives a "better" representation of molecules. However, I just read an article that said a lot of real life testing has shown that the octet rule may actually be closer to reality.

So I'm wondering how you guys have been taught.

 njdevsfn95 12-13-2012 05:46 PM

Ive seen both.

Octet rule is easier to grasp at an intro or early level because its as simple as "do i have 8?"

I teach octet rule and i havent taught a level that requires FC but i have done it.

 Rhaego 12-14-2012 07:38 PM

So we were doing the ICE tables in class today, and we get down to the part where you do the equilibrium coefficient. And they did it as x^2/[initial concentration] and disregarded the -x at the bottom. This is poorly written so could someone just explain ICE tables to me. Please.

 njdevsfn95 12-15-2012 06:20 AM

Quote:
 Originally Posted by Rockies94 (Post 56550955) So we were doing the ICE tables in class today, and we get down to the part where you do the equilibrium coefficient. And they did it as x^2/[initial concentration] and disregarded the -x at the bottom. This is poorly written so could someone just explain ICE tables to me. Please.
Equilibrium is a pretty basic concept in the fact the forward reaction will be balanced out by the reverse reaction.

Typically, the equilibrium favors one direction so heavily it allows us to make an assumption that there is very little change in the initial concentrations of reactants.

This assumption just makes things easier to solve because if you utilize the "-x" part and continue the ice chart, you're going to have an x^2 and another x when you get down to the E (or equilibrium values).

That would mean utilization of the quadratic formula to solve for x. This can be a big pain in the ass so an assumption is made to eliminate the "x" because chances are it is SO SMALL that getting rid of it has virtually no effect on the true value of x.

Take a look at this link and example 3 to be exact. http://www.science.uwaterloo.ca/~cch.../eqlbcalc.html

I hope I helped!

I usually show my students the quadratic formula method and then show them the assumption method for the same question. It is no surprise they would rather make the assumption because it makes the calculation so much easier.

 PSUCapsFan 01-13-2013 10:06 PM

Quote:
 Originally Posted by KesselBuiltMyHotrod (Post 56483989) So in my chem class we basically follow the octet rule for Lewis diagrams. I see around the internet a lot of places saying that using formal charge gives a "better" representation of molecules. However, I just read an article that said a lot of real life testing has shown that the octet rule may actually be closer to reality. So I'm wondering how you guys have been taught.
Depends which row in the periodic table your talking about. First row CNOF elements, octet rule works out. Beyond the first row, elements have additional orbitals which can accommodate extra electrons. Take a look at the structures of phosphate or sulfuric acid molecules.

Keep in mind octet rule is just a record keeping device which makes it easier to keep track of everything. In reality you have to look at the entire molecular orbital and calculate the areas with the most electron density.

 LatvianTwist 05-05-2013 03:09 PM

AP Chemistry test tommorrow. Any juniors/seniors in HS know what I'm talking about when I say I've never crammed harder for a test. :laugh:

Anyone else here taking it? How are you guys prepping?

 njdevsfn95 05-05-2013 08:06 PM

Quote:
 Originally Posted by LatvianTwist (Post 65349679) AP Chemistry test tommorrow. Any juniors/seniors in HS know what I'm talking about when I say I've never crammed harder for a test. :laugh: Anyone else here taking it? How are you guys prepping?
I know this feel.

Good luck!

 Lonewolfe2015 06-03-2013 11:32 AM

This isn't basic at all, but I remembered this thread existed and was hoping someone could help me avoid more hours of searching.

I found a patent through reaxys for an extra credit article in my Orgo class, it's past due but if I can figure out the missing link the guy will accept it.

http://worldwide.espacenet.com/publi...=&locale=en_EP

Somehow, this dude manages to Hydrobrominate an alkene at room temperature in the presence of oxygen and not hydrogen peroxide or some other catalyst. If I can figure out what mechanism the patent uses, I can get the credit (which I really need... struggling to keep a 3.0 here for my scholarship).

In essence, they dope propyl bromide with HBr, then initiate a regular anti-markovnikov by putting together propene with HBr, but use oxygen (O2) instead of H2O2.

Anyone have any idea what's going on, if you can get hydrogen peroxide from HBr and O2 at room temp (I've only found it when irradiated) or anything else that might help?

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