The h Bar

koolman

07:00

So according to me we will not get neither pure ethanol nor pure water

But it has written we can get pure water

Anonymous

No, when ethanol rich vapour is given off while boling the azeotrope

Anonymous

what happens?

Anonymous

even water boils

Anonymous

right?

Anonymous

but pure water is left behind

Anonymous

07:03

ethanol doesnt remain behind in the flask after complete boiling'

Anonymous

azeotrope = "a mixture of two liquids which has a constant boiling point"

koolman

In vapour water is also present

Anonymous

yes, but in flask only water is left

Anonymous

pure water

Anonymous

after complete boiling

koolman

07:04

Why there will be complete boiling

Anonymous

there will not be complete boiling, you have to boil the azeotrope such that ethanol is completely vapourized

Anonymous

leaving behind pure water

koolman

At constant boiling bpoint composition of liquid is also 95.6 ethanol

Anonymous

in the vapour there will be both ethanol and water

Anonymous

@koolman So what, you will vapourize it

koolman

07:08

Ok @S007 thank you vry much

Anonymous

@koolman did you understand it ?

koolman

Yeah

Thanks

Anonymous

welcome :)

Secret

If we are at the azeotrope point, where will we be moving if the mixture is boiled or condensed?

Anonymous

@Secret when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture.

Secret

07:15

so it cannot move left or right but go straight to vapor?

Anonymous

yeah

Secret

I see

Anonymous

Your arrows in the diagram are wrong...

koolman

At point C3 also if we boil it should go straight to vapor

More than boiling point

Secret

@S007 I am starting with a mixture < 95.6, and the arrows told me how I can get to the azeotrope or pure water respectively

Anonymous

07:19

@Secret You drew the arrows in the opposite direction. Read the linked page please...

koolman

@S007 am I correct

Anonymous

@koolman Where are you correct ? "At point C3 also if we boil it should go straight to vapor...More than boiling point"...what did you mean here ?

Anonymous

i could'nt understand your language

Anonymous

what did you mean by more than boiling point ?

koolman

If we boil it with temperature more than that of boiling point

Secret

07:25

@S007 Ok I understood how ethanol escapes first before water when the azeotrope is boiled (as only ethanol completely boils). But is this process occuring outside the axes of this phase diagram thus we cannot draw arrows to show the pure water forming?

John Rennie

@koolman You can't boil it with a temperature higher than the boiling point. If you attempt to increase the temperature all the happens is that it boils more vigorously and the temperature remains at the boiling point.

Anonymous

@Secret You cannot show the formation of pure water from this diagram. Pure water can be formed after you have formed the azeotropic mixture. You need to completely vapourize the azeotropic mixture and then you will be left with pure water which has a higher boiling point than the minimum boiling azeotrope

Secret

I see

Anonymous

@Secret hope you understood it now :)

Anonymous

@koolman john explained nicely why you can't boil it at greater than BP

koolman

07:30

@JohnRennie thank you nice explanation

Secret

Well that makes more interested on wondering what the phase diagram will look like along that pure water formation direction when I started to boil the azetrope (currently googling for that)

koolman

@ yeah i got it

@Secret if get it please share it here also

Anonymous

07:47

To summarize: @koolman

- Distilling a mixture of ethanol containing *slightly* less than 95.6% of ethanol by mass lets you collect:

- A distillate containing 95.6% of ethanol in the collecting flask (provided you are careful with the temperature control, and the fractionating column is long enough);

pure water in the boiling flask.

Anonymous

To get pure water start with a mixture having slightly less than 95.6 percent, so that you can boil off the azotrope

Anonymous

I think this was the doubt you were facing initially, right ?

Anonymous

@Secret Did you get that phase diagram ?

Anonymous

I don't think you will find it on the net

Anonymous

It is just like normal boiling of a liquid

Secret

07:50

But we have a mixture, thus I suspect it will look different from a pure ethanol boiling curve, no?

koolman

@S007 yeah

Anonymous

@Secret Probably, no! This particular mixture of ethanol and water boils as if it were a pure liquid. It has a constant boiling point, and the vapour composition is exactly the same as the liquid.

koolman

Is this type of azeotrope is called negavtive azeotrope

Anonymous

@koolman Yes, I should have pointed that out more clearly. To get pure ethanol start with >95.6 percent and to get pure water start with <95.6 percent

Anonymous

Hope you got it clearly now

koolman

07:54

How will we get pure ethanol

We can only get one component

4

Q: Azeotropes and separation by distillation?

I have just recently learnt the theory of fractional and normal distillations and the basics of maximum and minimum boiling azeotropes. Most books say that the components of the mixture forming an azeotrope cannot be separated by distillation because on heating, the residue (in case of negative...

Secret

@S007 but as you boil it, more and more ethanol vapor will escape, thus when complete boiling is reached, I will expect the liquid portion to have an increasing mole fraction of water, until it hits 100% pure water in the flask while the ethanol in liquid phase should drop to zero as it went completely into vapor?

Anonymous

Ow :/ you did'nt get the concept then. Suppose you have 96 percent ethanol-water mixture. What happens when you boil it @koolman ?

Anonymous

@Secret Absolutely not!

koolman

Ethanol will vapourise

As it is more volatile

Anonymous

when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture

koolman

07:56

Yeah

Anonymous

No. What if you distil a mixture containing more than 95.6% ethanol?

Work it out for yourself using the phase diagram, and starting with a composition to the right of the azeotropic mixture. You should find that you get:

a distillate containing 95.6% of ethanol in the collecting flask (provided you are careful with the temperature control, and the fractionating column is long enough);

pure ethanol in the boiling flask.

Anonymous

@koolman Ethanol will be left behind

Anonymous

The azeotrope will boil

Anonymous

You did'nt read the page carefully :/

Secret

yup but that will mean I will go from 100% liquid (95.6% ethanol water mixture) to 100% vapor (95.6% ethanol water mixture) when boiling the azeotrope, so I don't see how (as in the shape of such phase diagram where the water start to left behind) from this process can pure water be left behind (other than only knowing that water will not completely boil)

koolman

07:59

Its too confusing

If we start from more than 95.6 ethanol

Anonymous

@Secret I said that start with something like 95 percent ethanol water mixture. When you boil it the vapour concentration reaches 95.6 percent ethanol water mixture according to the phase diagram, and pure water is left behind while the 95.6 percent mixture gets collected in the flask

koolman

Then also we will get constant boinling point

And if we starf from less than 95.6 then also constant boiling point

Anonymous

@koolman yes

Secret

O, I guess that's where I screwed up, I started with 95.6% ethanol water, right at the azeotrope, I guess that's why I don't get any water left behind

Anonymous

@Secret exactly

koolman

08:02

In both cases we are getting same azeotrope

And by boiling same azeotrope we are getting different pure substances

Howw

Anonymous

@koolman Because when you take a 95 percent mixture then there is excess water compared to the finally formed azeotrope at 95.6 percent

koolman

Excess water where liquid or vapour

Anonymous

in liquid

koolman

But finally they both will become azeotrope

Anonymous

yes, but in a 96 percent mixture there will be excess ethanol and in a 95 percent mixture there will be excess water

Anonymous

08:08

both will form azeotropic vapours, but the excess substance will be left behind in the boiling flask

koolman

Yeah , but what will happen with the initial conditions

Anonymous

what initial condition ?

koolman

The composition would be same in both cases

Of azeotrope

In both liquid and vapour

Mew

hilo

Anonymous

@koolman No, composition will not be same in both liquid and vapour as u are not starting with 95.6 percent

Anonymous

08:12

you are starting with 95 percent ethanol

koolman

Why

Anonymous

so that you can get pure water left behind after azeotrope is formed after boiling

koolman

But meaning of azeotrope is same composition

Anonymous

Lets start again. What happens when you boil a 95 percent mixture ?

koolman

It will reach azeotrope

Anonymous

08:14

You get a azeotropic mixture or not ? According to the phase diagram ?

Anonymous

Right

Anonymous

What do you get when you condense the vapour ?

koolman

In which composition are same

Anonymous

you get a azeotropic solution

Anonymous

and what is left behind in the boliing flask ?

koolman

08:15

Yeah

Another azeotropic solution

Anonymous

No.

Anonymous

How can azeotropic solution be left behind ?

Anonymous

You started with 95 percent

koolman

Why when there is azeotropic mixture composition of both water and ethnol in liquid and vapour is same

This what meaning of azeotrope

Secret

@S007 Caption: Something like this?

Anonymous

08:17

but you did'nt start with a azeotropic mixture!

Secret

koolman

I did'nt start with that but later on got that

Anonymous

yes....so how can you say azeotrope is left behind ?

Anonymous

you cant

Anonymous

@Secret what is this ? :-P

koolman

08:19

As when we get azeotropic mixture we get composition of liquid as 95.6 ethanol

And at that time vapour is separated

Secret

@S007 My prediction on what is happening when a < 95.6% mixture is boiled to result in pure water left behind, where by liquid, I mean liquid in the boiling flask. I am trying to find the point where all azeotroep is boiled way leaving pure water behind

Anonymous

You get azeotropic mixture in the collecting flask and not in boiling flask

Anonymous

I think you need to learn about distillation

Anonymous

@koolman

Anonymous

Please learn distillation first

koolman

08:20

I got it

Anonymous

@koolman really ?

koolman

Really now i understood it

Anonymous

can you re-explain it to me ?

Anonymous

@koolman

koolman

Yeah

When we start with less than 95.6

Anonymous

08:22

please do then...in a short para :)

koolman

We will reach azeotrope

Then we will collect ethanol rich vapour

Secret

typo: the geometry of the curve near the point where all azeotrope just boiled away and the shape of the concentration curve when the azeotrope boils away in the 95% ethanol

koolman

And water will left behind

Am i correct

Anonymous

yes :)

koolman

Oh thank you

Anonymous

08:24

@Secret I will see the graph later after few hours...my head is not working anymore :-P

Anonymous

Bye guys :)

koolman

You really helped me alot

Byee

Anonymous

welcome

Anonymous

:)

Mew

09:11

pokemon time

user228700

09:42

@Mew: Hello!

Mew

Hey girl

do you play pokemon

user228700

Nope .__.

Mew

that's a shame

user228700

Hm :-/

koolman

@Kaumudi are you a girl

Mew

09:45

Well moonlight is a girls' name isn't it?

koolman

Moonlight ???

Mew

Yeah

Kaumudi was named after the supermoon

koolman

Oh

John Rennie

@Kaumudi I'm with you on this one :-)

Mew

u don't play pokemon?

the new game came out

you can catch them all

user228700

09:49

@Mew No, I wasn't! xD

user228700

@JohnRennie :-)

Anonymous

@Kaumudi Maybe you were named after the newspaper company

Anonymous

news.keralakaumudi.com/beta

Anonymous

LOL

Mew

wtf

Anonymous

09:51

@Kaumudi See kaumudi.com

user228700

@S007 I've obviously seen it already, lol :-P

user228700

Kaumudi=Moonlight in Sanskrit. Thasall. (Nothing to do with supermoons and all -.-)

Anonymous

hehe...so what does it mean actually ? I think your parents might have been reading the morning newspaper while thinking of a name for you. LOL XD

Anonymous

oh so it does mean moonlight !

Anonymous

:)

user228700

09:54

@S007 I told this story awhile back. You can search for it if u want, using the word "pregnant", lol :-P

Anonymous

Good to know :-D

Anonymous

@Kaumudi "My mom was reading a Sanskrit scripture whilst pregnant with me. And in it, there's the word "Kaumudi". Apparently, in the middle of reciting, when she said " Kaumudi", I kicked for the first time :-D"

Anonymous

Okay my guess was somewhat right!

Anonymous

Wohoo :-D

Mew

yeah the baby hated the name Kaumudi such that it caused it to kick

user228700

10:00

@S007 Not really but okay :-P

user228700

@Mew Yeaah, Idk, I like to think of it like, you know, I moved when I heard what was fated to be my name and all :-)

user228700

This Raoult's law is still eating my brain >.<

Mew

why are you learning totally differentt hings each day Kaumudi?

two days ago it was nuclear physcis i think

sounds like a broad curriculum?

user228700

@Mew Lol, it's still nuclear physics. Yes, yes, broad curriculum it is.

Mew

oh is it

user228700

10:04

In the morning, it was calculus...

user228700

I know how to juggle :-P

Anonymous

Juggling topics is actually good when you have such a gigantic syllabus :-P

Anonymous

Over 100 chapters !

user228700

Ikr? Sigh.

Mew

what do you mean over 100 chapters?

user228700

10:07

@Mew We mean exactly what we say :-P

Mew

that's insane

r u girls both doing the same curriculum?

user228700

Lol!

user228700

Poor @S007 is not a girl...right? xD

Mew

oops my bad

@koolman, why do you ask, u thirsty?

koolman

What

user228700

10:09

Yeah, we're preparing for the same effed up exam. LOADS of people here, actually. Koolman, Swapnil, Ramanujan etc.

Mew

oh wow, what is the exam for

koolman

Yeah

Anonymous

@Kaumudi How do you know ? I might be a girl. I never revealed :-P

Mew

yeah i thought u were a girl s007

user228700

@S007 :-P Gut feeling.

Anonymous

10:10

@Kaumudi I grant you the benefit of doubt ... LOL XD

user228700

Lol :-P

Mew

tell me more about this exam

Secret

$$\lvert \textrm{Me}\rangle=\sqrt{\frac{45}{100}}\lvert \textrm{Girl}\rangle + \sqrt{\frac{55}{100}}\lvert \textrm{Boy}\rangle$$

Mew

is that right Secret?

John Rennie

Let's keep the conversation away from matters reproductive chaps. I speak in my official capacity as a room owner.

Anonymous

10:21

@JohnRennie Yes, please !

Secret

I knew to some extent that competition between sisters are more psychologically damaging than those of brothers

all that backstabbing

Boys are more strightforward

They pretty much either compete for status or girls

girls's conficlts are a lot messier

Mew

yeah that's true

about boys

what do girls compete for?

John Rennie

→ 24 messages moved to Trash

Mew

ty John

some peeps have dirty minds

Secret

in light of the trashing, perhaps I should just end the topic here?

Mew

10:24

no

John Rennie

You (collectively) are also treading dangerous ground when discuss differences between the sexes. We are all physicists here.

3

Mew

the trashing was the sex talk, not the "what do girls compete for talk"

please tell me what girls compete voer?

if not guys and status

Secret

A lot of things, looks, fashion, photos, and a lot of seemly small things

there are even articles and research on such phenomenon

Mew

but looks and fashion is for guys no?

Secret

yes but (if my memory serves) girls are more fierce on that

also a lot of girls like gaming

e.g. social media statisitcs foudn most gamers are girls

Mew

10:26

no way

John Rennie

Feel free to continue this in the Stereotypes Stack Exchange chat room. The conversation is out of place here. There will be no further warnings.

Mew

most gamers a guys

ok John

Secret

@JohnRennie Ok noted, I am stopping here

Sir Cumference

@JohnRennie Eh, we can be open here

The chat isn't purely about physics/math

Secret

Johnrennie: should we trash all the above talks to prevent possible ramifications?

Mew

10:28

In my opinion, no Secret

but perhaps there is a list of rules somewhere we can refer to to be sure?

user228700

I'm glad I stepped out for those 15 mins :-P

Mew

where is everyone up to in pokemon sun and moon?

you missed the excitement @Kaumudi

user228700

Not sure if I agree ^ lol :-P

Mew

oooo ok

user228700

@JohnRennie: Raoult's law again >.<

John Rennie

10:31

Yes? ...

Mew

RAoult's law, is that what excites you

How is Raoult's law related to nuclear physics?

Wikipedia suggests it is thermodynamcis

user228700

I've a quick question related to this graph:

user228700

@Mew Aii, it's not. Before, I meant to say that I'm still doing nuclear physics on the side.

Mew

oh i see

user228700

10:35

^ "the temperature has a fixed value".

John Rennie

Ah, @koolman was asking about graphs like that a bit earlier. Systems like that don't obey Raoult's law.

Mew

looks like a negative deviation from RAoult's law

user228700

My book says "The area b/w these two curves is vapour-liquid equilibrium region. Vapours cannot exist above the bubble point curve and liquid cannot exist below the dew point curve"

user228700

@JohnRennie The trouble is that that ^ is supposed to be curve for an ideal mixture of two volatile liquids.

user228700

Well, I mean, it has justified this using appropriate equations...

Mew

10:38

Vapor–liquid equilibrium

In thermodynamics, the vapor–liquid equilibrium describes the distribution of a chemical species between the gas phase and a liquid phase. == VLE data introduction == The concentration of a vapor in contact with its liquid, especially at equilibrium, is often expressed in terms of vapor pressure, which will be a partial pressure (a part of the total gas pressure) if any other gas(es) are present with the vapor. The equilibrium vapor pressure of a liquid is in general strongly dependent on temperature. At vapor–liquid equilibrium, a liquid with individual components in certain concentrations will...

John Rennie

Oh wait a minute, sorry, I assumed it was temperature on the vertical axis.

user228700

Yes, that ^

user228700

(The temperature is constant, I mean @Mew)

John Rennie

Hang on though, I still don't see how that can be for an ideal system.

Mew

yep

user228700

10:40

@JohnRennie Enlighten me as to why not, please...

Mew

I hope the linked article is helpful

I will read it soon after catching this pokemon

John Rennie

@Kaumudi let $x_a$ and $x_b$ be the mole fractions of A and B in the liquid, and $p_a$ and $p_b$ be the partial pressures in the vapour.

user228700

Alrighty.

Mew

pa = Ptot*xa

user228700

Hang on, look at this:

John Rennie

10:43

Ah, OK, yes I see.

user228700

John Rennie

It's because the vapour pressures of the pure components A and B can be different.

user228700

@JohnRennie OK..? Wait, what was it that made u doubt the correctness of the graph initially?

John Rennie

10:45

@Kaumudi I was just misremembering physical chemistry I studied 35 years ago :-)

Swapnil Das

35!

user228700

:-) Still, what was it that u were misremembering? Perhaps I'd be able to learn s'thing from that..?

user228700

@SwapnilDas: Ello!

Swapnil Das

@Kaumudi Hey!

Mew

HI swapnil

ar eyou studying for the exam too?

Swapnil Das

10:47

Hi!

No, I've been prepping for Physics Olympiad 2017.

John Rennie

@Kaumudi I was thinking that the composition of the vapou had to be the same as the composition of the liquid for an ideal system, but of course it differs by $\P_a/P_b$ where the capital P is the vapour pressure of the pure component.

Swapnil Das

Gotta busy schedule, tbh.

Mew

oh what's that?

Swapnil Das

IPhO.

I wanna do IPhO ;)

Mew

I dunno what that is but sounds cool

Hope you win gold

Swapnil Das

10:49

Haha, thanks a lot.

Anonymous

@SwapnilDas Good luck for that..are you in 11 ?

John Rennie

@SwapnilDas not 35 factorial, I'm not that old :-)

Swapnil Das

@S007 Thanks a ton. I'm in 10th.

@JohnRennie I believe in you :P

user228700

@JohnRennie Ah, OK. Shall we move on..?

Swapnil Das

@Mew International Physics Olympiad.

John Rennie

10:50

@Kaumudi I can't remember weher we had got to ...

user228700

Man, talk about poor memory!

user228700

(:-P)

Secret

The usual raoult's law is plotted as mole fraction of components in solution. Here based on the screenies you have given seemed to be plotted in terms of the mole fraction of the vapor

John Rennie

@Kaumudi It happens when you get old

user228700

@Secret Vapour and liquid.

user228700

10:52

@JohnRennie :-) Alright, so I don't really get the graph.

Swapnil Das

@JohnRennie No one's mentally older than me, guaranteed.

user228700

I mean, I do, but not fully.

Mew

@SwapnilDas is your memory relaly bad?

Swapnil Das

@Mew No. But I 'visualize' myself as an old guy.

Mew

that's good preparation

Swapnil Das

10:53

Lol.

user228700

Aii, okay, I'm preparing to tell u everything I don't understand...

Mew

commence

user228700

Still preparing.

Mew

if John can't help I'll pause the game

Secret

The stuff you present is consistent with this link, which is quite different from what I learnt back in physical chemsitry about raoult's law

It is possible my phsyical chemistry lesson have not wetn through dew points and bubble point

user228700

10:55

Okay, one question that immediately comes to mind is, what dyou really mean when u say "the liquid starts boiling"?

Secret

I can see all your equations from your book are there. Now to make sense of them

user228700

I mean, when does that happen?

Secret

When the temperature and pressure is just right such that the first drop of liquid enter the vapor phase

user228700

^ liquid mixture.

user228700

@Secret Uhh, I'm not so sure I agree...

user228700

10:57

Thanks for the link BTW! :-)

John Rennie

Start with the vapour pressures of pure A, $P_a$, and pure B, $P_b$.

user228700

Wokay!

John Rennie

And for the sake of argument lets say $P_a > P_b$ (which is what your graph shows).

user228700

Okay...

John Rennie

If the pressure is greater than $P_a$ then the whole system will be liquid.

And if the pressure is lower than $P_b$ then the whole system will be vapour.

user228700

10:59

Gimme a minute to process that...

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