| Selective reduction |
[Jul. 6th, 2008|01:32 pm] |
I'm trying to reduce a nitro group without reducing the N=N also present in the compound. Does anyone have any ideas as to how to do this?
The method that I have been thinking of is using anhydrous sodium sulfide in methanol. The reaction would take place under acidic conditions, and since there is also an OMe present, there is a possibility of that being disrupted.
I'm a bit of a newbie organic chemist so any suggestions would be much appreciated! |
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| Can someone confirm this for me, please |
[Jun. 29th, 2008|06:46 pm] |
| [ | mood |
| |  curious | ] |
Suppose a calibration curve was prepared for permanganate ion with a range of 0 to 4.00e-4M. If a steel sample is 6.20%Mn, to what volume in mL must a .300g sample be dissolved/diluted to produce a concentration of permangante ion at the center of the curve?
concentration= (4.00e-4M)/2 = 2.00e-4 M
mass of Mn/.300g of steel = .062 so mass of Mn=(.062)(.300g) = .0186g Mn
.0186g Mn x (1 mol Mn/54.938g) x (1 mol MnO-4/1 mol Mn) = 3.386e-4 mol MnO-4
(3.386e-4 mol MnO-4/volume) = (2.00e-4 mol)/1.000L)
Volume = (3.386e-4 mol)(1.000L)/2.00e-4 mol)
Volume = 1690mL |
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| Chemical equations |
[Jun. 26th, 2008|05:50 pm] |
A combustion analysis of a sample of MDMA afforded the following report: C, 68.37%; H, 7.82%; N, 7.25%; O, 16.56%.
a) the empirical formula is?... C11 H14 N O2
b) a 2.500g sample of Mdama was treated with HCl to give a new compound, (MDMA)HCl:
MDMA (s) + HCl (aq) --> (MDMA)HCl (aq)
**note MDMA is being used as a molecular formula, however it is an acronym.
Assume the conversion of MDMA to (MDMA)HCl was complete. the resulting solution was then reacted with 11.54 mL of 0.1120M NaOH, an amount chosen because it lead to the reaction of NaOH with (MDMA)HCl:
(MDMA)HCl (aq) = NaOH (aq) --> (MDMA) NaCl (aq) + H2O (l)
What is the molar mass of MDMA?
I found the empirical formula and the percent of oxygen, I am very confused on ho to find the molar mass of MDMA. I also found that the moles of NaOH that are being reacted are 1292 moles (multiplying the L and the M gives me the moles) |
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| Best Clinical Chemistry book? |
[Jun. 10th, 2008|07:37 pm] |
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I am 19 years old, a 3rd year undergraduate Medical Technology student in the Philippines. We are going to have Clinical Chemistry for three semesters. Although our professor referred us to one book, I am afraid that she will take informations from the other books when exams come. I wish to buy another Clinical Chemistry book as for my other reference. Will you please suggest good Clinical Chemistry books? |
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[Jun. 9th, 2008|08:38 pm] |
Can anyone explain to me the hybridization and molecular geometry for Pyridine (C5H5N, and I'll include a picture below). I'm getting very confused trying to figure it out. I know there are six pi electrons, but that's about all. I've read repeatedly that it's in a "planar ring," does that mean that the molecule is flat? That seems strange. If anyone can explain to me a little bit, I'd appreciate it. :)
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| Gen Chem help |
[Jun. 4th, 2008|06:05 pm] |
I'm tutoring someone in a gen chem class during the summer, and today there was this one problem I couldn't figure out how to do.
Barium ore contains barium carbonate. You have a 1.4g sample that is dissolved in HCL then filtered to remove any insoluble material. It is then reacted with sulfuric acid to parcipitate out barium sulfate. The barium sulfate is dried and weighed. It is 1.1g. What is the mass percent in the original sample?
I can't remember the exact problem, but it was really close to this. It was the only problem that I couldn't help her with, and I feel a little bad about it.
Thank you. |
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[Jun. 1st, 2008|02:08 pm] |
| [ | mood |
| |  anxious | ] |
| [ | music |
| | Sweeney Todd | ] |
Hey, for my HS chemistry class we have to do powerpoints to review for our final. I was wondering if anyone would take a look at my powerpoint and tell me if there's any incorrect information, ways to improve it, and so on? Thank you very much. You can download it here.
Also, if you could tell me if there's any way to make the second half less...boring, I would be forever in your debt. Especially because this project is worth 250 test points in my average. >_< Thank you!
Cross-posted to ![[info]](http://p-stat.livejournal.com/img/community.gif) anti_chemistry. |
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| Acids & Bases & Equilibrium - oh my. :( |
[May. 26th, 2008|05:04 am] |
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I need help with this question.
A 35.0mL sample of (monoprotic) lactic acid, C3H6O3, is titrated with 20.0mL of a 4.0x10-4 mol/L sodium hyroxide solution. What is the pH of the resulting solution at the equivalence point, if Ka for lactic acid is 1.4x10-10? I don't know how to even really approach this since our teacher didn't tell us what to do if there is a concentration & an amount used... it's just never happened before. And, I don't know how to do this without the concentration of lactic acid... both those things combined leave me a confused girl.
But, this is what I have so far:
C3H6O3 + NaOH --> NaC3H5O3 + H2O
Kc = [NaC3H5O3] [H2O] / [C3H6O3] [NaOH]
...but I really don't think any of that is correct. |
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| Non-chemist |
[May. 22nd, 2008|06:22 pm] |
Hello Chemistry Buffs,
I am a non-scientist who often uses chemicals in my work as a jeweler. I have a question regarding storage of some chemicals.
I am about to use Ferric Nitrate to etch some silver for the first time. I ordered the chemical, and it is in the form of small crystals. When I use it I will make a solution with water. When I am done using this solution, can I store it for later use, or do I have to dispose of it? If I can store it, what is an appropriate container to use? Glass? Plastic? Should I go to a chemical supply and get a special container?
Thank you for your help. Please excuse my ignorance. |
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| Organic |
[May. 20th, 2008|12:48 pm] |
So I just started organic chemistry and since the labs and lectures aren't quite coordinated very closely, I'm kind of lost on one of the lab follow up questions.
In summary, solution of benzoic acid in NaOH is placed in a flask, then an equal volume of diethyl ether is then added and the mixture is stoppered, shaken and allowed to stand to reach equilibrium.
a)which liquid forms the top layer?
I think this seems simple enough-- the ether layer would because it is less dense than the aqueous.
b)Which solvent contains the benzoic acid?
This confuses me because from what I've read (and we haven't really covered this in lecture yet), i thought the benzoic acid would be soluble in both because carboxylic acids are soluble in NaOH and diethyl ether... So i don't really know how to approach this question, would it simple have stayed in the NaOH because the two liquids don't mix?
THEN, HCl is add to neutralize the mixture and the flask is shaken again and allowed to reach equilibrium...
c) Now which solvent contains the benzoic acid?
So would this be the ether because the NaOH and HCl have neutralized each other and the benzoic acid is no longer soluble in the aqueous solution, so it dissolves in the ether layer?
In the laboratory, my TA was throwing around the term "liquid-liquid extraction" as some sort of hint, I presume. Is the question above an example this?
Thanks! |
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| organic.. |
[May. 20th, 2008|06:21 pm] |
i just need some help describing the structural formula(s) for the below molecules. organic is very foreign to me, but here are my vague stabs at what their names might be? a. pentyl-something? C4H2O2 b. octyl-something? C8H6O2 c. pentyl-something:? C10H302 sorry, i forget how to make subscripts..but any help at all will be much appreciated ! :) |
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| 122% yield?!! |
[May. 20th, 2008|09:39 am] |
I've got one entry left on webassign, so I thought I'd confer with you good people. Here's the question:
After crystallizing, she weighs her sample and finds her percent yield is 122%!! Check all the reasons that might explain this seemingly impossible result.
__ A side reaction occurred.
__ Not all of the reactants were dissolved.
__ Some product was lost in filtration.
__ Her reactants were contaminated.
__ Her sample is wet.
__ Her product is contaminated.
__ The reaction did not go to completion.
My thinking is this:
Wet sample means water is being weighed as a product, so that's a reason, and one way of saying the sample is wet is saying the product is contaminated.
The rest of these answers, now that it's not 3am, look like they'd give a reduced yield.
Y/N? |
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| Malonic and Acetoacetic Ester Synthesis |
[May. 14th, 2008|11:59 am] |
Anyone want to take a shot at this?
I understand the first steps--deprotonation and alkylation--I just don't understand the last step. What does D stand for and why is it used? I have a limited understanding of the decarboxylation mechanism in general... I just am confused as to why one yields the acid and one yields the keto...
( under here )
Of course thought-provoking answers that send me down the right course are what I'm after. :) |
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[May. 12th, 2008|12:57 am] |
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Where I can find something about carbosilicagel? I need information for my term paper! Thank you. |
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[May. 10th, 2008|08:35 pm] |
The Mpemba effect is the tendency of warm water to freeze faster than cool water under certain conditions. The question is as follows:
Calculate the energy required by a refridgerator (positive answer) in KJ per mole to completely freeze hot water starting at 93. C, and the energy required to completely freeze the same volume of cool water starting at 24. C.
What is the difference between these two energies?
While this may seem a large percent of the energy required, this energy is small enough per mole that many of the proposed mechanisms to explain the phenomena make "thermodynamic sense."
So, using deltaE = q = s x m x delta T
I put together this equation: 4.184J/gxC x 18.02g x 93C = 7011.8J/mol = 7.0KJ/mol for the freezing of water at 93 degrees Celsius. I'm wrong.
Why am I wrong? What else should I be factoring in here? deltaE also equals q + w, and for pressure/volume work, that's -PxdeltaV. I know that water expands about 9% when it freezes - how do I put that in here?
Thanks so much! |
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| Chemical Equilibrium |
[May. 8th, 2008|08:44 am] |
I'm having trouble with a chemical equilibrium problem in my quant class:
"Find the concentration of Cu2+ in equilibrium with CuBr (s) and 0.10 M Br-."
I know: CuBr (s) ----> Cu+ + Br- has a ksp=5x10-9
I know that Cu2+ is the most common form in aqueous solutions, so the Cu(I) ion converts to the Cu(II) ion. But is it the redox reaction? Is there another ksp value I have to look for? I went over the section and didn't see anything about these types of reactions.
After that, it's the common ion affect pushing the reaction towards the left, making the copper(I) bromide less soluble.
Thanks a bunch! |
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| Kinetics and pseudo-rate laws. |
[May. 6th, 2008|10:15 pm] |
Hi!
Well, I try to minimize my posting here to help reduce clutter, but my Chem 12 AP exam is coming up fast and I may be on here quite a few more times with questions and need for advice.
Right now I'd say my two worst subjects are Kinetics and Redox.
Regarding kinetics, a few times the use of pseudo-rate laws has come up, but I can't find my notes and everyone else is either busy or they don't understand it either.
So, could anyone here please re-teach the premise of pseudo-rate laws for me? I'd give you baked goods if I could. |
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| Instrumental Question |
[May. 5th, 2008|11:15 pm] |
| [ | mood |
| | curious | ] |
| [ | music |
| | "Time is Running Out" - Muse | ] |
A quick question, because I've looked in like 3 textbooks that mentioned it and didn't really get a definitive answer.
Is Electron Spectroscopy for Chemical Analysis(ESCA) a destructive technique? From what I read it seemed that it was only the outermost layer that may be damaged, but with organics the sample may be destroyed due to the heat generated? So for inorganics it's not destructive, but for organics it is?
Thanks for any help. |
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| Two Questions |
[May. 3rd, 2008|06:20 pm] |
One general, one specific.
Consider 3.5 L of a gas at a pressure of 2.0 atm in a cylinder with a movable piston. The external pressure is changed so that the volume changes to 10.5 L.
(a) Calculate the work done, and indicate the correct sign.
(b) Use the preceding data but consider the process to occur in two steps. At the end of the first step, the volume is 6.0 L. The second step results in a final volume of 10.5 L. Calculate the work done, and indicate the correct sign.
(c) Calculate the work done if after the first step the volume is 7.0 L and the second step leads to a volume of 10.5 L.
Does the work differ from that in part b?
I don't even know how to begin with this one, unfortunately. If I'm being told that the cause of the change in the volume was the external pressure, then isn't the external pressure the system? Does this make the work positive? But how do I calculate it? The equations I have deal with changes in height, not changes in volume. I am all besquiggled in confusion. Any insight would be appreciated.
A 50.0 L stainless steel container was charged with 4.00 atm of hydrogen gas and 5.00 atm of oxygen gas. A spark ignited the mixture, producing water. What is the pressure in the tank at a constant temperature of 25°C?
atm
What is the pressure in the tank at a constant temperature of 125°C?
atm
I got the first part correct (3.00 atm). But I also got 3.00 atm for the second, and I don't know why I'm wrong. Temperature is part of how I find out the quantities of substance in reaction, and the ratios stay the same throughout. Don't they?
Thanks so much! |
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| Advanced Applications |
[May. 1st, 2008|04:24 pm] |
| [ | mood |
| |  okay | ] |
In my advanced applications class, we're using Gaussian software to study the vibrational bands and thermodynamic functions of methanol. One of the questions in the report asks to derive an equation relating the vibrational band to the force constant. I know the vibrational bands are the essentially just the frequencies and the force constant is just the amount of force needed to break the bond. The professor didn't provide ANY equations and is not available until monday. I'm not sure how to go about deriving an equation to relate the two. Any help is appreciated! |
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