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 1 
 on: Today at 10:32:09 AM 
Started by clemi2310 - Last post by Arkcon
Here's an online resource to some tips you should always start with:

http://www.chromatographyonline.com/hplc-mobile-phases-10-bad-habits-avoid-0

 2 
 on: Today at 08:48:41 AM 
Started by clemi2310 - Last post by Arkcon
That you have 3 pKa's isn't too much of a problem, since two are close to each other.  The wide range for the other one is something of a problem.

You've gone to two extremes:  Very low pH, to somewhat higher for the ion-pair buffer.  You may have to experiment with some other points to build a conclusion as to where you need to go.

 3 
 on: Today at 08:44:15 AM 
Started by Urbanium - Last post by Arkcon
OK.  How does a GC work, and what does it do?  Working from a definition, you can begin to suggest what might be doable.

At >70 posts over the last 5 years, you should be aware of our Forum Rules{click}.  You already accepted the rules when you signed up for our forum, and you have to follow them, whether you agree with them or not, or even if you're unaware of them.

We don't dump complete answers on this forum, not for a new student, not for a professional in a hurry,  and not for an amateur trying to invent the latest thing.

Consider:  would you use a FID detector to detect the colored pigments in plant material?

Consider:  would you use a GC to analyze soluble ions in plant material?

And I don't know where the lack of SPME fibers was supposed to lead us.

 4 
 on: Today at 08:37:36 AM 
Started by dume85 - Last post by Arkcon
To tell the truth, its hard to follow your posting.  I don't actually see a question anywhere.  Certainly, you can rewrite it -- the protocol you followed can go in an outline to start with.  After all, the lab was written already, people know what was done.  After your results, you can discuss sources of errors, again, as an outline.

We have a rule, on these forums, against "word soup".  Your I did this, and then I..., and then I, So these numbers, oh, by the way, I forgot to mention previously I ...

That makes for a convoluted novel, science isn't done that way.

 5 
 on: Today at 08:32:14 AM 
Started by junglekidd - Last post by Arkcon
Hi there, junglekidd:, I'm sorry you haven't had much help until now.  However, its hard to follow what you mean when you describe what you're doing, and what you still need.  Let's try to break it all down:

Hello all!

Good day!

I need a little help regarding viscosity table.

Probably the easiest one you'll find is the CRC.  Maybe some other engineering textbooks or maybe physical science textbooks.

Quote
I’m doing a project to build a Hot plate magnetic strirrer here for my Final year project.

Hrm.  A motor and a magnet?  OK.

Quote
Like normally I want to make a morning coffee, I will add coffee powder inside the cup, pour hot water, and stir them all, so it will become a homogeneous we call Coffee.

There's nothing false in this statement.  There's nothing very insightful either.

Quote
From the process I learnt that heat and stirring will affects viscocity of the liquid.

Heat does, and stirring might, for certain types of liquids.  Not likely for a coffee solution.  I felt I had to make that clear.

Quote
My question is, is there any sources regarding liquids mixing and its relation with speed of stirring and heat?

It can be hard to find a source for some things, but there's no source for anything that isn't true.  Where you found evidence of a statement you made is a good place to look for a table.

Quote
I would need something like table for a refence to my project.
Thank you so much!

 6 
 on: Today at 08:22:09 AM 
Started by spankytank - Last post by pgk
1). This is a question of chemical kinetics. Both reactions occur simultaneously but by adding more equivalents of epichlorhydrine, you favor the formation of 3a, because:
u = k[alkoxide]10[epichlorhydrine] > k[alkoxide]2[epichlorhydrine] > k[alkoxide][epichlorhydrine]
Note that 3a and 3b have different rate constants of formation.
2). HCl is a gas and thus, it will quickly evaporate before opening the oxirane ring. Contrary controlled hydrolysis of acetyl chloride will slowly release HCl in situ, during the progress of the reaction that gives the necessary time to react.

 7 
 on: Today at 07:44:02 AM 
Started by spankytank - Last post by spankytank
Oh yeah, my bad. Meant to say stabilizing effect from the acetic acid.

 8 
 on: Today at 07:34:25 AM 
Started by spankytank - Last post by wildfyr
for 2) What do you mean add pure HCl? The gas? or 12 M solution, which is still about 65% water.

 9 
 on: Today at 07:25:32 AM 
Started by AdiDex - Last post by pgk
1). You are right!
Your calculations are correct. I was wrong and strict. So, I fully apologize for this.
2). Coming to the point:
Imagine that you have a combustible that has a theoretical combustion heat = -21.93 kcal/mole. But during combustion an endothermic reactions occurs, which consumes +10.00 kcal/mole but the reaction product is also combustible with combustion heat = -17.17 kcal/mole.
Neglecting their molar ratio for simplicity reasons, the overall combustion heat is:
-21.93 + 10.00 - 17.17 kcal/mole = -29.10 Kcal/mol
Thus and in terms of thermal yield: |29.10| > |21.93|
But in terms of Hess law: -21.93 > -29.10
3). Something similar happens hereby:
On the one hand, sulfur consumes (unknown?) energy, in order to keep a planar molecule but on the other hand, the planar structure contributes to the stabilization of the hybridization and the aromaticity of thiophene.
4). Restarting from the beginning:
The hydrogenation enthalpy is an approximate method for the calculation of aromatic energy, which has a high scientific and educational value. This method may work with benzene but it tends to be inaccurate with heteroaromatics, fused and polynuclear aromatics, aromatic ions, as well as with aromatics that have a number of members that is different than 6 because it does not take into account the size of the heteroatom, neither the difference of ring strain between the aromatic rings and their perhydro-derivatives (note that 6 members rings have ring strain ≈ 0).
More accurate results can be taken by using specific quantum equations, which are specially invented for.

 10 
 on: Today at 03:30:08 AM 
Started by radical886 - Last post by Babcock_Hall
Your question seems broad upon first examination.  It might be worthwhile to start out by separating typical reactions in the cell versus those found in the test tube.  I am not sure how physiologically relevant the conditions in the paper you cited are (which is not to say that the work is flawed).  For example, glutathione peroxidase reacts hydrogen peroxide with two molecules of GSH to produce GSSG.  GSSG is reduced using NADPH by glutathione reductase.

With respect to non enzymatic chemistry, supposed one molecule thiol is oxidized to a sulfenic acid.  It is possible that the fate of the sulfenic acid is controlled by the concentrations of thiol versus hydrogen peroxide and the two associated rate constants.  If the concentration of thiol is large, one obtains a disulfide because the thiol captures the sulfenic acid.  If the concentration of peroxide is large, one obtains the sulfinic acid.

I found a review by Mauro Lo Conte and Kate S. Carroll in Oxidative Stress and Redox Regulation called "The chemistry of thiol oxidation and detection."  There might be some good information there.

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