November 30, 2021, 07:12:16 AM
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21
I am going to try and distill different fatty acids, that boil close to "231 °C at 1.70E+01 mm Hg".  So that is the bogie.  I have no idea what that 1.70E+.01 mm Hg means, but using google it appears its like .022 atmospheres.  That sounds like a big pressure reduction, but I don't know how hard that is to achieve! 

Any recommendations for an affordable, decent vacuum distillation set up?

Would something like this kit:

https://www.amazon.com/Distillation-Apparatus-Equipment-Chemistry-Glassware/dp/B07R8JFK97/ref=sr_1_3?keywords=vacuum+distillation+kit&qid=1638117238&sr=8-3

And this pump:

https://www.amazon.com/Homesprit-Filtration-Laboratory-Distillation-Apparatus/dp/B083Z98JKH/ref=sr_1_5?keywords=vacuum+distillation+pump&qid=1638056598&sr=8-5


Do the trick? 

Any suggestions appreciated!!!
22
Organic Chemistry Forum / Re: Can anyone translate this study to English for me?
« Last post by Homeslice on November 28, 2021, 11:59:13 AM »
Thank you Borek!!!!

So see is this is right for a "revised" #7:

7.  After making sure the solution in the separatory funnel has cooled, do this three times:  add 500 ml of petroleum ether, shake the separatory funnel well, wait for several minutes.  Separate the two layers into two different flasks, one with the ether (and what has now been absorbed into it) and the other with the remainder.  Repeat twice, adding 500 ml more ether to the non-ether flask each time, shaking and separating.  After that is done three times, combine all the ether amounts into one flask.  Add 200 ml of distilled water to that flask, shaking well, and waiting for several minutes thereafter.  Assuming you can identify the water layer, discard it.  Add 50 grams calcium sulfate to the ether amount, shake well, filter out the solids and you are left with the fatty acids in the petroleum ether, boil off the ether in a vacuum distillation apparatus to recapture and be able to reuse the ether.

How'd I do?

Thanks!!!
23
Undergraduate General Chemistry Forum / Re: Homework - need help
« Last post by Orcio_Dojek on November 28, 2021, 11:51:34 AM »
Quote
1. I am supposed to find out, how much does 4,48 l of oxygen weight while in normal conditions (whatever that means), and how much does it weight while it has 60 degrees Celsius.
Normal conditions: 298.15 K (25°C, 77°F) and 1 bar (14.5038 psi, 100 kPa).

Then you need to use pV = nRT equation.
24
Undergraduate General Chemistry Forum / Homework - need help
« Last post by jeto2m on November 28, 2021, 11:40:07 AM »
Hello, and I apologise in advance, but I don´t really like chemistry, however it´s a mandatory subject of mine, and I can´t solve two problems our teacher has given us. If there´s someone that could help me, I would be really grateful.
1. I am supposed to find out, how much does 4,48 l of oxygen weight while in normal conditions (whatever that means), and how much does it weight while it has 60 degrees Celsius.
2. What volume (V) of vapor (with the temperature of 95 degree Celsius and pressure of 101000 Pa) will be created by reaction of 1g oxygen and 1g of hydrogen.
I know, that this qustion is probably very primitive, but for me its beyond my abilities. I would like to thank in advance to anyone responding. Last but not least, sorry for my bad english or any mispronunciations.
I´ve managed to come up with something for the first problem, however the second I don´t understand at all.
Here´s my work:
1. V(O2) = 4,48 l
T1 = 273,15 K
P1 = 101 325
m1 = ?
T2(O2) = 60 stupňov
m2(O2) = ?
1 mol plynu = Vm =22,4 l
1 mol O2 = 22,4 l
1 mol .....22,4 l
x mol ....4,48 l
x = 0,2 mol
Rm  = 8,314472 J · K-1 · mol-1 
32 g/mol
(P.V.M)/(R.T)=m
                                                                      m1 = 6396 g = 6,4 kg

T2 =  333,15
P2xV2 = 1661,85612
53 169,3958/2769,96635 = 19,20
m2 = 19,20 g
25
Citizen Chemist / Re: Hominy, lye, lime, soda etc.
« Last post by Orcio_Dojek on November 28, 2021, 11:33:47 AM »
@schmidling Ca(OH)2 will give the corn better taste than NaOH and especially KOH.
26
Citizen Chemist / Re: Hominy, lye, lime, soda etc.
« Last post by Borek on November 28, 2021, 11:08:00 AM »
It all may boil down to primitive methods of making "lye" from wood ashes.

Looks like, from what I read nixtamalization is done by soaking corn in alkaline solution - and while solutions you have listed are in many ways different, from some point of view they are all equivalent. Just alkaline solutions of strong bases, no matter what the mode of preparation was.

Definitely different bases will require a bit different procedures, but the only way to find out is by trial and error. The only important health hazard is their corrosiveness and related ability to destroy tissues, so you need to avoid direct contact (nothing unusual: apron, gloves, glasses, fume hood or at least mask as in some conditions they can get a bit volatile and you don't want to breath them in any form).
27
Citizen Chemist / Hominy, lye, lime, soda etc.
« Last post by schmidling on November 28, 2021, 10:16:10 AM »
Hominy is made by soaking dried corn in lye, soda, potash, slaked lime, KOH or NAOH and I am trying to find reasons for choosing one over the other.

The info from the typical search is an endless stream of bad info and contradictions.

It appears that the lime process takes more soaking/cooking time than using either form of lye but the reason for KOH vs NAOH escapes me.

It all may boil down to primitive methods of making "lye" from wood ashes.

I would like to know get a chemist's opinion and also info on health hazard differences that may exist.

Thanks,

Jack
28
Physical Chemistry Forum / Re: Computational chem self-education
« Last post by H2CO3 on November 28, 2021, 05:23:25 AM »
Hey,

personally I find self teaching quantum-chem pretty difficult, but I think if you want to use those, you should also understand the theory behind it.

That being said, I can recommend a few books:

Modern quantum chemistry : introduction to advanced electronic structure theory / Attila Szabo, Neil S. Ostlund   
Introduction to computational chemistry / Frank Jensen

You don't need to know everything in there, maybe some rough guidelines what you should understand:

What is a Slater-Determinant and why do we need it?
How to derive the canonical Hartree-Fock equations?
What is DFT, DFT functionals and the Jacobs Ladder of DFT.

If you can answer those, you can have a closer look at some other topics like:
Post HF-Methods (MP2,CI)
Coupled Cluster Methods (better explained here: Olsen: Molecular Electronic-Structure Theory)
29
Undergraduate General Chemistry Forum / Re: buffer preparation calculation
« Last post by mana on November 27, 2021, 03:33:49 PM »
0.4 M buffer (if I read it right) means sum of concentrations of the acid and its conjugate base is 0.4 M. That gives you an additional equation. Solution as shown does something equivalent (uses molar fractions), but doesn't explain where they come from (I haven't checked numbers, but the general logic of the approach seems OK: for a given A/B molar ratio molar fraction of A is A/(A+B)).

Not your fault, but pH 6 is way too far from acetic acid pKa for a serious buffer.
thank you very much  :)
30
Undergraduate General Chemistry Forum / Re: buffer preparation calculation
« Last post by Borek on November 27, 2021, 03:23:34 PM »
0.4 M buffer (if I read it right) means sum of concentrations of the acid and its conjugate base is 0.4 M. That gives you an additional equation. Solution as shown does something equivalent (uses molar fractions), but doesn't explain where they come from (I haven't checked numbers, but the general logic of the approach seems OK: for a given A/B molar ratio molar fraction of A is A/(A+B)).

Not your fault, but pH 6 is way too far from acetic acid pKa for a serious buffer.
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