The Periodic Table

3:36 AM

So I'm not new to SE, but I am new to Chemistry SE. Just out of curiosity, would my question from yesterday be on topic on the main site?

I will likely have more questions like those in the future...right now I'm taking my first semester of General Chemistry (bio major, pre-med)

CowperKettle

4:07 AM

> We neutralized the samples by 20 µl of 0.3 M hydrochloric acid and used 500 µl of benzene two times to extract excessive PMP (1-phenyl-3-methyl-5-pyrazolone).

Is this a description of liquid-liquid extraction?

CowperKettle

4:42 AM

> Peptide:N-glycosidase F (PNGase F) is an enzyme that catalyzes the complete removal of N-linked oligosaccharide chains from glycoproteins. Often called an endoglycosidase, it is more correctly termed an amidase or glycosylasparaginase as cleavage is at the asparagine-sugar amide linkage.

Why does it have the colon?

Can we write it thus: " peptide-N-glycosidase F "? With the hyphen?

Martin - マーチン

5:04 AM

Is anyone else experiencing problems accessing the IUPAC gold book articles? For me it only loads the front page, but none of the articles.

Hmm, I can load a few of them, but for example the index of C stays empty.

CowperKettle

Good morning again..

@Martin-マーチン empty

> Fluorescent detector properties:
Excitation wavelength: 330 nm
**Excitation emission wavelength**: 420 nm

Can there be such thing as "excitation emission wavelength"?

Martin - マーチン

Thanks for checking.

CowperKettle

no problem

Martin - マーチン

5:22 AM

about the excitation emission wavelength, I am not sure what that means here. It does not really make sense for me, as I don't really know the context.

CowperKettle

I think the authors committed a typo, I made a note for them.

getafix

5:57 AM

I just realised that using \dfrac gives a undefined control sequence error on the mobile app. Was editing a few answers when I noticed that. Is it some sort of a bug? I changed it to \frac so that the text is displayed..did not know what else to do

orthocresol

It does. I don't know why. I always stick to \frac{}{}.

getafix

Ah okay. So guess it is a known issue..I thought must be something wrong with my app

Martin - マーチン

6:09 AM

@getafix MathJax is different for each platform and sometimes there are differences. In general there is no need for \dfrac on our pages, let the environment decides how to set the fraction.

getafix

Okay. Cool..so I changed dfrac to frac when editing those posts, hope that's okay then?

Martin - マーチン

yeah that should be fine

getafix

6:57 AM

Cool.

getafix

8:56 AM

@AaronAbraham I answered your question, did it in a bit of rush..hopefully, i did not make a mistake. If i did, let me know

1

Q: Did I modify this equation for Current correctly?

High-schooler here reading up on electrochemistry..... I came across this equation (and its derivation) in the book Physical Chemistry, by Wallwork and Grant: Now the thing is, the equation is valid for 'uni-univalent' electrolytes (like KCl). But I want a more....'versatile' formula. So I...

electrochemistry

user116211

9:07 AM

@getafix Bad title.

orthocresol

9:44 AM

Does Mathjax not work in tag wikis?

CowperKettle

> We unfroze the denaturing plate. (is this okay? or is it "we defrosted"? O_O)

orthocresol

defrosted sounds more english

CowperKettle

Ludwig says "we thawed the samples"

Maybe it's the same thing with the denaturing plate

orthocresol

that sounds ok too

getafix

or we thermally treated the denaturing plate till the frozen water underwent a phase transition to its liquid state haha

2

user228700

10:39 AM

Hello :-) Can someone please explain to me what the term "active mass" means? My textbook states that this quantity is dimensionless. However, it also uses this term interchangably with the term "concentration" (molarity) which does have units of $mol/V³$. So what is the correct definition of active mass..?

Loong

11:02 AM

@KaumudiHarikumar So, you are still working on that topic, and your question didn't yield a useful answer?

user228700

@Loong Yep.

Loong

I see.

@KaumudiHarikumar I bumped your question up. Let's see if it gets more attention now.

getafix

Is active mass = chemical activity?

Loong

@getafix it's the same concept

getafix

ah okay

Loong

11:14 AM

But probably from a time when chemistry was made by mass in gram and not by amount of substance in mol.

getafix

I see.

user228700

@Loong Oh my God, thank you!

getafix

I am guessing it has its roots in the law of mass action?

and indeed it does..

Loong

@getafix or maybe the other way round; it may be an origin of the law of mass action

getafix

yeah perhaps reading about it right now..

The notion is the same as that of chemical activity, I agree..the definition seems to differ.

Bounty Hunter

11:20 AM

2

Q: What is active mass?

I'm aware of the fact that active mass is defined as the molarity of a substance, but my textbook states that "Active masses are dimensionless quantities but for our purposes we generally take them with dimensions of molarity, partial pressures etc." What point is my textbook trying to get ...

equilibrium concentration

getafix

JM97 in his answer seems to imply that active mass = chemical activity..I dont think that is the case..

user228700

@getafix I don't even understand what u mean when u say "chemical activity " :/

getafix

Perhaps you haven't encountered it yet in your education

The idea is that when you put "x" amount of stuff in a solution, in a real (non-ideal case) your effective concentration/activity etc... is not "x"

orthocresol

i have actually never used the term active mass..

getafix

@orthocresol me neither

orthocresol

11:26 AM

was never taught it.. so take that however you want..

getafix

Law of mass action

In chemistry, the law of mass action is the proposition that the rate of a chemical reaction is directly proportional to the product of the activities or concentrations of the reactants. It explains and predicts behaviors of solutions in dynamic equilibrium. Specifically, it implies that for a chemical reaction mixture that is in equilibrium, the ratio between the concentration of reactants and products is constant. Two aspects are involved in the initial formulation of the law: 1) the equilibrium aspect, concerning the composition of a reaction mixture at equilibrium and 2) the kinetic aspect...

That's what I just learnt about it..lol

user228700

@getafix Yes. Also, in reply to your comment; the equilibrium constant does have dimensions sometimes. The stoichiometric coefficients may not add up to be equal on both sides of the reaction and if this is the case, since we substitute the concentration of the products and reactants in the expression for the eq. constant, it ends up with a unit.

getafix

@KaumudiHarikumar No it doesn't it is always dimensionless

But I don't think we are talking about the same things..

user228700

What about $Kp$? It has units of $(atm)^{∆ng}$

getafix

Think about it $\Delta G = -RT ln(K)

how can the argument of a function..ln() have dimensions?

how do you define ln(mol) or ln(atm)..

user228700

11:30 AM

@getafix Yeah, that's the trouble. My textbook is really weird but this is what we have been taught :/

user228700

What about $K_p$..?

getafix

Well K_p , K_c they are special..what you've been taught is not the complete picture..

user228700

@getafix OK..?

getafix

I dont think I can set up the necessary concepts/math in chat

user228700

@getafix Damn. Can you direct me to some article that I can read, perhaps?

getafix

11:33 AM

Umm maybe.

user228700

Or maybe even explain it qualitatively?

getafix

Do you at least know about chemical potential?

user228700

@getafix Umm, nope :-(

getafix

yeah thought so..guessing you are in high school (approx. )

user228700

@getafix Yeah, I graduated just this year.

user228700

11:35 AM

Can you maybe just explain why $K_p$ and $K_C$ are special..?

getafix

Sure I can try

I dont think it would be a satisfactory explanation

user228700

@getafix Something is far better than nothing...well, in this case anyway.

getafix

So an equilibrium constant (the real deal ) is dimensionless..and in terms of activities it is exact

user228700

@getafix What do you mean "it is exact"?

getafix

let me finish

user228700

11:38 AM

@getafix Sure. Sorry for interrupting.

getafix

so in most settings it is more convenient to work with concentrations

so we need to relate K = K_c (or p)

user228700

(Let me know when you're done)

getafix

activities can be writing as a = (gamma)(mole fraction, or some other sort of concentration term)

gamma is the activity coefficient..a measure for amount of non ideal behaviour

and so putting activities (calc. as above) for reactants products into K (the real deal)

K = K_gamma x K_conc

for most purposes a good approx. is to drop K_gamma

user228700

@getafix No, hold on, please wait.

getafix

sure, i am done anyway..

I am sorry don't think I can do a better job lol

user228700

11:43 AM

I'm sorry but after having read so far, I have realized that an explanation in such detail doesn't exactly help me. My textbook/exam only ever deals with $K_C$/$K_p$ and after having read one/two texts, I understand that "activity" is the one that is substituted in "the real deal".

user228700

And I understand that activity is just the concentration divided by the concentration at some standard conditions so the units all cancel out.

getafix

Yeah kinda..

user228700

And that explanation suffices. Thanks so much for ur effort :-)

user228700

@Loong: Idk how Bounty's are supposed to work but if they decrease your own reputation, then please remove it, if possible. This much understanding is enough and I'm not looking forward to the answer to that question as I am sure that it will be too complicated, as illustrated by @getafix here (:P)

getafix

but not entirely..don't forget the gammas lol

i think loong looses the rep

user228700

11:48 AM

@getafix Yeah :/ Idk if it is possible to remove it but I hope he/she does remove it and doesn't lose rep.

getafix

Although I don't know anything about active mass.. never used it never learnt it

user228700

@getafix OK :P Thanks anyway :-)

getafix

Thermodynamic activity

In chemical thermodynamics, activity (symbol a) is a measure of the “effective concentration” of a species in a mixture, in the sense that the species' chemical potential depends on the activity of a real solution in the same way that it would depend on concentration for an ideal solution. By convention, activity is treated as a dimensionless quantity, although its value depends on customary choices of standard state for the species. The activity of pure substances in condensed phases (solid or liquids) is normally taken as unity (the number 1). Activity depends on temperature, pressure and...

This would be helpful perhaps?

user228700

user228700

I found this and this is all the explanation I need, although this is the answer to a different question...sort of.

user116211

11:52 AM

@KaumudiHarikumar The units must be upright. Use \mathrm{ }

getafix

yup

People neglect dimensions all too often

user116211

@getafix Always.

orthocresol

@KaumudiHarikumar yeah, you understand correct. I have written on this before.

user228700

@getafix Are u terribly busy at the moment? I've always had doubts regarding Le Chatelier's principle and I'm wondering if u could quickly clear them, please..?

orthocresol

8

A: Which equilibrium constant is appropriate to use?

As noted in this previous question, the correct definition of the equilibrium constant $K$ depends on activities. If you are interested in the derivation of the equation $\Delta G^\circ = -RT \ln K$ (which requires "proper" thermodynamics), read Philipp's answer to that question. For a reaction ...

user116211

11:56 AM

In $$V= \sum_i \frac{\partial U}{\partial{\dot q_i}}~q_i- U$$ the time is dimensionless.

user228700

@MAFIA36790 I don't understand what u mean...

getafix

Nope not really..

@MAFIA36790 which I could sight read Latex lol

user228700

@getafix U mean u're not really busy..?

getafix

yeas

user116211

Well, these are the physicists' tool to procrastinate things ;/

user228700

11:58 AM

OK, cool! Do u mind talking to me about Le Chatelier's principle for a bit then?

user116211

@KaumudiHarikumar I can.

user228700

@MAFIA36790 I thought u were the physicist :P

getafix

@KaumudiHarikumar Sure..or you can post a question and others can talk to you about it too lol

user116211

@KaumudiHarikumar So?

user228700

@getafix Thing is, I have posted a question and it didn't yield good results.

getafix

12:00 PM

link to said question?

user116211

@KaumudiHarikumar, read this especially the second para of this post:

user116211

2

A: What is the difference between the equilibrium position and the equilibrium constant?

Equilibrium position: A reaction reaches equilibrium position when it has no further tendency to change; that is, the reaction does remain 'spontaneous in neither direction' . This happens when the reaction Gibbs energy becomes zero viz. $\Delta_r G= 0\;.$ Equilibrium constant: The reaction ...

user228700

@MAFIA36790 So, I didn't think that u were interested in discussing chemistry. No offence to anyone here, but Chem. doesn't excite me all that much :P Especially inorganic.

user116211

@KaumudiHarikumar It's not chem; it's thermodynamics.

user116211

@KaumudiHarikumar BTW, I'm a 1st year undergrad; not a physicist ;)

user228700

12:02 PM

@getafix: chemistry.stackexchange.com/questions/58184/…

user228700

@MAFIA36790 Yeah, I know this. U told me that we're the same age :P Nevertheless, I just figured that u wouldn't be interested. Anyhoo, let me go read that question u referenced.

pentavalentcarbon

@CowperKettle it probably means "emission wavelength for the above excitation wavelength"

user116211

@KaumudiHarikumar Remember Le Chateliar's Principle is just a rule of thumb. The reason for why it works depends on how the value of $\Delta_r G^\Theta $ and $K$ get affected by the process.

getafix

@KaumudiHarikumar Increasing the volume = increasing the pressure.. decreasing the volume = decreasing the pressure (we are talking about the gas phase) so increase the pressure (external stimulus), the system responds by decreasing volume, lowers pressure

user228700

Hang on, please. I'm reading up.

getafix

12:18 PM

ok

getafix

12:29 PM

so..?

user228700

I'm sorry that took so long. Something important came up in b/w.

user228700

Yeah, so, I still have that doubt regarding the liquid-gas equilibrium...

getafix

whats your doubt?

user228700

Exactly that which I had mentioned in my question. If we increase the pressure of the system, the system is supposed to move in that direction in which the pressure decreases→volume increases, yes? Isn't the volume of gas greater than the volume if the liquid?

user228700

Basically, Idk how to think about all this properly...

orthocresol

12:34 PM

That is like saying that if you push a door, it opens towards you

user116211

@orthocresol Man you are genius!! Great analogy ;))

getafix

@KaumudiHarikumar an increase in volume would increase the pressure in a closed container...

user228700

@orthocresol OK..? I don't quite understand. Can you help me to think about these concepts more clearly? It's a fog in my brain right now :/

getafix

@orthocresol LOL

orthocresol

I mean, I see where you are coming from. But this is not quite about LCP. It is just physics.

user228700

12:36 PM

@orthocresol OK..?

orthocresol

If you try to compress something by increasing the external pressure, then the volume will decrease.

user116211

Sarcasm at its peak:

user116211

in The h Bar, yesterday, by MAFIA36790

We're sorry you're disappointed with our service; your refund is being processed now. — Alfred Centauri 8 mins ago

getafix

Imagine a liquid with some vapour in a container with a piston..

apply pressure on the piston..the volume decreases..

user228700

@getafix OK..?

user228700

12:39 PM

@orthocresol Please go on...

orthocresol

That's all

Don't overthink it.

getafix

There's really not that much to it

If you have a gas and liquid in a chamber with a piston attached..

would the pressure increase or decrease when the gas volume increases?

user228700

The pressure would decrease...

user228700

Okay, I maybe over thinking this. I'll ask it a bit differently; when we increase the volume, again, we talk about the change in terms of pressure. But why can't we say "It'll move in that direction in which volume decreases, instead of saying " system moves in a direction in which pressure increases"?

getafix

The pressure wouldn't decrease..

user228700

12:43 PM

If this doubt is resolved, I think the fog will lift.

getafix

I think i found your problem..

The chamber has fixed boundaries and piston..if you increase the amount of gas in this (by going from liquid to gas) the pressure on the walls of the container increases..

user228700

@getafix Please enlighten me sir/ma'am :P

getafix

Which is why when you are compressing something..it would like to go from gas to liquid..

to decrease pressure..

user228700

@getafix Alright, so we're always considering a closed system. OK..?

getafix

What do you mean by always?

user228700

12:46 PM

OK..? But what if the volume remains constant and we increase temperature, thereby increasing pressure..?

user228700

@getafix Never mind.

getafix

So do you get it or not?

user228700

No, I didn't. Check my last message...

getafix

your last message is nevermind

user228700

:P The one before that, lol.

getafix

12:48 PM

yeah so what if what?

keep doing that and you can make a big explosion lol

??

user228700

@getafix Huh? No! I mean, we change pressure w/o changing volume. So what happens? Big explosion? :/

getafix

by heating?

user228700

Yup.

getafix

yeah so liquid goes to gas..gas keeps building up..eventually gas wants to get out

user228700

@getafix So it doesn't attain equilibrium again..?

getafix

12:52 PM

it does after blowing up...the gases inside will now be at 1 atm..

user228700

Yeah, OK...

getafix

lol I am sorry, I am being a little bit frivolous

user228700

So we can't talk about such processes, yeah?

user228700

@getafix :P That's alright.

getafix

we just did talk about such a process

user228700

12:53 PM

I'm not sure if u're even getting all my messages :/

getafix

I dont know

But is your original question answered..?

user228700

@getafix Yeah, but not with regard to Le Chatelier's process. The container blowing up is not something we want m, exactly :P

getafix

the one you posted?

it's not really LCP

just plain old physics

user228700

No, not yet.

getafix

if you have some other sort of a mental picture..and it lets you understand the process

then that's fine

user228700

12:55 PM

No, the mental picture is causing confusion-it's not helping me at all :/

getafix

anyway, I must go now..if you found this discussion or the one about activities useful feel free to up vote a bunch of my answers..as a token of gratitude haha

good night!

user116211

@getafix o/

user228700

Oh, OK. I will :P Thanks :-) Goodnight!

getafix

@MAFIA36790 \o

ciao

user228700

@MAFIA36790 Are you free? The doubt hasn't been cleared yet :/

user116211

12:57 PM

@KaumudiHarikumar hmm; well have an exam tomorrow; so myself studying....

user228700

You think it will help to ask at the h bar(PSE chat)?

user116211

@KaumudiHarikumar What?

user228700

@MAFIA36790 Oh, OK. Continue then. I'll ask at the PSE chat.

user116211

@KaumudiHarikumar There is a meta discussion going; so you may get a delayed response; but I don' know.

user228700

Oh, yeah :/ Sigh. Dunno what to do now.

user116211

1:00 PM

@KaumudiHarikumar Just ask it here; anyone, interested would respond.

user228700

I've already asked here :P If anybody else is free, please do consider sharing ur views.

user116211

@KaumudiHarikumar Then wait... or dig it in the internet....

user228700

OK. Thanks for ur help and best of luck for ur exam t'row :-)

user116211

@KaumudiHarikumar Well, I don't care about the exam; I'm not interested in optics.

user228700

@MAFIA36790 OK, whatever u say :P

Aaron Abraham

3:46 PM

@MAFIA36790 Try this....it might change your perspective about optics....amazon.com/Optics-4th-Eugene-Hecht/dp/0805385665

@Loong ...... mind one more query?

Aaron Abraham

4:01 PM

0

Q: What exactly does κ stand for in this equation connecting Solubility and Molar conductivity?

I came across the following equation while studying electrochemistry: It's mentioned that κ is the conductivity of the saturated solution of the salt in conductance water, minus that of the water alone. Now the thing is, from what I've read, conductance water has NO (or negligible) conductivit...

electrochemistry water solubility erratum

user116211

@AaronAbraham yeh; a standard recommended text.

user116211

@AaronAbraham: Write \kappa to get $\kappa\,.$

Aaron Abraham

It's a good book......

It's what piqued my interest in optics...

1,3-feeds

4:30 PM

0

Q: Why was this reference request closed as unclear?

I don't quite understand why the following question was closed: Molecular structure of all periodic table element molecules exceptional cases etc It is especially not clear to me what's unclear about it. To me it is fairly obvious, that it asks for a reference about the structures of all pure ele...

discussion scope closed-questions

Bounty Hunter

5:45 PM

17

Q: Why is a S-S bond stronger than an O-O bond?

I'm wondering why exactly the single bond between two sulfur atoms is stronger than that of two oxygen atoms. According to this page, an $\ce{O-O}$ bond has an enthalpy of $142 \rm~\frac{kJ}{mol}$, and a $\ce{S-S}$ bond in $\ce{S8}$ an enthalpy of $226 \rm~\frac{kJ}{mol}$. This one reports the $\...

inorganic-chemistry bond molecules

orthocresol

@BountyHunter `(.•.)´ @Jan

Your chem reputation has caught up with German, I see...

Since it is getting bountied, I should really try to explain it more clearly. It has always been a mess, I tried to clarify it once, but I still think it is all over the place..

Loong

@orthocresol It's good that Bounty Hunter isn't seal hunting.

orthocresol

:(

Poor seals get killed every year in Canada.

#SaveTheSeals

4

If anybody is free can you guys help me find the question that asks about why Cp - Cv = nR?

Loong

@orthocresol at least once per year I visit our seal rescue station: google.de/…

orthocresol

@Loong (.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.•.)´(.‌•.)´

Loong

5:54 PM

:-D

orthocresol

That's really nice

I've seen them on a beach before.

@Loong google.com.sg/…

Loong

@orthocresol here, it looks like this: google.de/…

orthocresol

Heh :)

Loong

But we don't like it when tourists disturb the seals.

orthocresol

Yeah. There were many signs warning people to not go too near

Loong

6:01 PM

Yeah, the seals will try to flee, and young animals might be separated from their mothers.

orthocresol

:(

Loong

Such orphans are collected and brought to the above-mentioned rescue station.

Jan

@orthocresol Yeah, I had to get rid of some xD Totally wasn't preparted for over 30 upvotes to that silver nitrate question …

@orthocresol `(.•.)´`(.•.)´`(.•.)´`(.•.)´`(.•.)´`(.•.)´`(.•.)´`(.•.)´`(.•.)´`(.•.)´‌`(.•.)´`(.‌•.)´

@Jan Fixed that for you @orthoseal ;)

Loong

@orthocresol Furthermore, seals can waste a lot of valuable energy when they try to escape, since they only have a few hours on the sand banks before the tide comes back. And if they waste too much energy, they might not survive the winter.

orthocresol

6:16 PM

@Loong The seals are happy, then :D

@Jan My left paw!

2

orthocresol

7:02 PM

1 hour ago, by orthocresol

If anybody is free can you guys help me find the question that asks about why Cp - Cv = nR?

I will +500 bounty anybody who finds it... I have spent one hour trawling through both thermodynamics and gas-laws in vain...

I remember seeing it, although it had a horrible non-descriptive title.

Loong