Log in

Chemistry Help [entries|archive|friends|userinfo]
Chemistry Help

[ userinfo | please read rules!!! ]
[ archive | here ]

guanidines [Mar. 16th, 2013|01:44 pm]
Chemistry Help

Сould anyone give me some links (preferably on reviews) dealing with redox properties of guanidines?

Thanks a lot.
linkhave a solution?

Oppolzer's Camphorsultam and Arndt-Eistert [Oct. 27th, 2012|04:13 pm]
Chemistry Help


Hello everyone!

My supervisor has given me a reaction from before I started my PhD to talk through during a presentation and I'm considering questions that may be asked in the Q&A. I'm struggling to work out how Oppolzer's camphor sultam works. I found one explanation that said "steric hindrance of the dimethyl group in conjunction with repulsion of the amide nitrogen lone pair". I just wanted to make sure that's right, as I've only found descriptions of selectivity when a sulfone oxygen coordinates to a Lithium enolate, whereas I have a silyl enol ether in my actual reaction.

Also, does anyone know why sonication and a catalyst would be needed for an Arndt-Eistert reaction? I thought the reaction happened pretty easily?

Thanks so much in advance :)

link1 solution|have a solution?

Exam Preparation [May. 31st, 2012|12:03 pm]
Chemistry Help


I have a Chemistry exam in 2 weeks and was hoping to get some help with questions I'm going through from previous years exams that were were given without answers and I'm stuck on.

I'm stuck on this one because despite having attended every class, I don't remember us ever having touched on calculating molar conductivity but am worried that they put E in there to trick us. The answer I'd go for if I saw this in my exam would prolly be A because it's the difference between CsNO3 and HF.

This I'm stuck on again because of option E. My understanding is that vapor pressure decreases after the addition of a solute so the highest would be pure water leaving me with C and D. I don't know where to go from here.

Thanks a million in advance.
link2 solutions|have a solution?

Gallium oxides [Jan. 6th, 2012|02:15 am]
Chemistry Help

Dear сolleagues,
I had an unsolved problem. I have a gallium oxide, which is a mixture of three modifications: α-, β- and ε-Ga2O3.

The question: is how to get rid of the β-Ga2O3 in this mixture?

P.S. Option, described in Wikipedia (heating β-Ga2O3 at 65 kbar and 1100 C) is not considered, the pressure does not build.
Is there some other way?
link2 solutions|have a solution?

Chemical Equilibrium [Sep. 7th, 2011|12:36 pm]
Chemistry Help
Hey it's me again! I have a question about chemical equilibrium.

At temperatures near 400 C, the Kp value for the synthesis of ammonia is 2.5 x 10-4. At 400 C, what would be the approximate value of K for the following reaction?

3H2(g) + N2 (g)⇔ 2NH3 (g)

So, the equation for the partial pressure is Kp = Kc(RT)Δn

Δn-2-4= -2

To solve for Kc, it's Kc= Kp/RTΔn

so it's Kc= 2.5 x 10-4 / (0.821 L atm/Kmol x 673.15 K)-2

Only I get a different answer than what's in the book.

Can anyone tell me where I went wrong? Thanks!
link2 solutions|have a solution?

Reaction Rates [Aug. 19th, 2011|04:08 pm]
Chemistry Help
Hey, I was wondering if anyone could help me with a problem regarding reaction rates

For the following reaction in a 4.00-L container, it was found that 1.00 x 10-4 mol of C4H8 reacted over a time period from 10:58 A.M. to 11:15 A.M.

C4H8 (g) --> 2C2H4 (g)

What is the average rate, in M/s, for this reaction?

I took the time period of 10:58-11:15, which is 17 minutes, and did dimensional analysis to figure out what it was in seconds (1020 s). I set the equation up as

1.00 x 10-4 M
1020 s

and got 9.8 x 10-8 but the answer is 2.5 x 10-8. I don't know what I'm doing wrong.

Thank you to anyone that can help!
link3 solutions|have a solution?

10% solution [Jun. 29th, 2011|09:29 pm]
Chemistry Help


I need to make  10% formic acid   (my formic acid has a 88% purity)

i'm confused as to how to do this. let's use 100 mL to make it easier to calculate.

Do I:

A.  10 mL formic acid + 90 mL H20


B. 10 mL formic + 100 mL H2O?

When do I use A and when do I use B to calculate?

I was making a 0.1% Formic acid in water 1 L solution, I used calculation B to make the solution.  1.14 mL of formic acid + 1000mL H2O.
link7 solutions|have a solution?

(no subject) [Apr. 24th, 2011|05:09 pm]
Chemistry Help

Does anyone know how to remove the acetate from this molecule, leaving a terminal olefin? It's not homework, I'm doing a past exam paper as revision and the final molecule has no OAc, but the first part of the question was about selective acetylation? 
Thanks so much! :)
link2 solutions|have a solution?

Estimating Delta G at a given temperature? [Mar. 7th, 2011|04:43 pm]
Chemistry Help

In class a few days we are given this problem. I understand the first part because, but I have no idea how to estimate Delta G at 400 K. The answer is provided, but can anyone help inform me on how that answer was obtained?

Use a table of thermodynamic properties to determine So and Go at 298K for the following reaction:
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
So = 1180.45 J/mol-K


Go =2-959.14 kJ/mol


Estimate the value of Go at 400 K.
Go =3-978 kJ/mol
link2 solutions|have a solution?

Dissolving MnO2 with HNO3 [Mar. 6th, 2011|11:14 pm]
Chemistry Help

I ask a lot of questions and you all are always very helpful. (:

We recently had a lab where we used diluted HNO3 to clean a filter that we had collected MnO2 from. Why was HNO3 used when MnO2 is insoluble in nitric acid?

Someone showed me this reaction:

2MnO2 + 4HNO3 -> 2Mn(NO3)2 + 2H2O

which does not make sense to me since Mn(IV) is being reduced to Mn(II), but I don't see anything being oxidized. What am I missing here?

Thanks in advance for any help/insight.
link4 solutions|have a solution?

[ viewing | most recent entries ]
[ go | earlier ]