The Periodic Table

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DHMO

01:39

@orthocresol but... but it isnt a good nucleophile if i deprotonate it

DHMO

02:05

what is the pKb value of acetic acid?

5 hours later…

DHMO

06:58

@orthocresol I don't understand this comment. I thought I already drew out all the C-H bonds that react:

3 hours later…

DHMO

09:41

@Secret hi

Secret

Bagging a grain of metallic hydrogen

DHMO

Fun fact: formaldehyde (HCHO) exists in water mainly as methanediol, with the equilibrium constant of the corresponding equation being 10^3.

Secret

formaldehyde smells like water for some reason

DHMO

09:56

@Secret I'm not sure if water has an odour

Secret

Pure water probably not. Rain water however has an earthy smell due to geosimin

DHMO

10:18

@Secret could you help me find pKb of acetic acid?

M.A.R.

@DHMO What are the conditions?

DHMO

@M.A.R. room temperature

atmospheric pressure

M.A.R.

(I feel really sick, so I might go offline any minute though)

DHMO

take care

M.A.R.

@DHMO What's wrong with pKw - pKa?

DHMO

10:20

@M.A.R. eh, that isn't the real pKb

I see it as the pKb of acetate

(although I should know that pKa and pKb refers to one equilibrium reaction)

M.A.R.

Oh wait

Eh, I feel lazy. Let's Google

DHMO

I've tried that

Secret

$$pk_b=-log \left(\frac{[H_2Actate^+][OH^-]}{[HActate]}\right)$$

I am not sure how will one find the activity coefficient of protonated acetic acid though

DHMO

that's the point

paracresol

10:44

@DHMO @M.A.Rtin Hallo o/

DHMO

@paracresol hi

paracresol

Secret

Here's something I can suggest: Try compare the $\Delta_f H$ of the following species $HActate$, $Acetate^-$ and $H_2Acetate^+$. I suspect the $\Delta_f H$ gap between $HAcetate$ and $H_Acetate^+$ might be a lot larger than Acetate to acetic acid thus making it highly unlikely to accept another proton

NIST does not seemed to have any thermochemical formation data for this species, only hydrogn bonding enthapies

DHMO

@Secret but there's still a value to it...

or else Fischer esterification won't work at all

Secret

11:07

hmm, it seems the reaction rate of this reaction is quite slow. Since the rate determining step is the nucleophilic attack is at the C=O, the slow rate means the transition state has a rather high barrier

Experimental observation also show that if you dump acetic acid into water, it will tend to dissociate to acetate rather than it abstract an H form water to make OH- (unlike the case when you use alcohol, which then you get the Fischer esterfication going as the protonation is acompanyed by the nucleophilic attack of the alcohol O). I suspect then the gibbs free energy of the following re…

Secret

11:21

Ok some correction: Even if a water analogue of fischer esterfication occurs, the starting and end products are identical

So the question boils down to why the protonated acetic acid and acetic acid equilibrium is so far to the acetic acid side.

@DHMO Made a question for you. I don't think the answer is a trivial one because the thermodynamic parameters for the protonated species in question might be too low concentration to measure accurately.

Q: Obtaining activity coefficients of conjugate acids of some common carboxylic acid molecules

Recently, I have been wondering about justifying the notion on how some common acids (e.g. carboxylic acids) are themselves weaker bases than water to the point that we don't usually consider them to act as base. To begin, we use the formula for $pK_b$ and consider for example acetic acid $$pk_b...

DHMO

11:43

thanks @Secret

paracresol

A: What is the group reagent for the zero group (ammonium cation) in inorganic salt analysis?

The "Group reagent" is a cocktail of reagents that serves as a prima facie indication of a particular cation, characterized by the formation of a precipitate during a positive test/result and...well... no precipitation in the event of a negative test/result. You often come across use of "Group ...

Loong

12:05

@DHMO The autoprotolysis constant of acetic acid in acetic acid is quite similar to that of water in water (about something * 10^(-13)).

Perchloric acid is almost completely dissociated in acetic acid.

DHMO

12:23

@Loong interesting

DHMO

12:47

@Loong @Secret which one should be dominant, [CH3C(=O)OH2]+ or [CH3C(OH)2]+?

Secret

I don't think O is happy to have two H$^+$ attached to it

Hexacoordinate-C

Hello

@Secret have you ever seen an oxygen like "O" only ?

Secret

O atoms are quite reactive. You can see them in some laser experiments in the gaseous state

Hexacoordinate-C

If you take $\ce{O^{2-}}$ with $\ce{H^+}$ you'll have $\ce{HO^-}$

Secret

It also depends on whether you are dealing with singlet or triplet O, they react differently

Hexacoordinate-C

13:01

@sec

paracresol

@Hexa \o/

Hexacoordinate-C

I'm not sure DHMO is speaking about laser experiment in gaseous phase

Secret

in aqueous media, single O species are unstable, they will immediately abstract H from water and other protic species to form radicals or ions

Hexacoordinate-C

And I have ever seen a lot of times and oxygen with two hydrogen ions in molecule

Especially in organic chemistry in some mechanisms

Secret

Those usually are good leaving groups, thus they will leave on the next step

Hexacoordinate-C

13:06

Yes

But it doesn't mean that is it impossible

Look it is actually possible to make six bonds carbon haha

DHMO

@Hexacoordinate-C he just meant the oxygen atom on CH3C(=O)OH

Secret

The equlibrium is probably so unfavourable for them that there is only small concentration of them in the solution. This is one reason I ask that question, because we cannot talk much without the thermodynamic paramters on how really unstable that species is

Hexacoordinate-C

I wasn't speaking about that molecule. Just in general case

Secret

Also for [CH3C(=O)OH2], suppose the water fragment does left, you end up with acetyl radicals or Me-C$^+$=O, the latter I am not sure about its stablility

DHMO

What on earth is this discussion about? @Hexacoordinate-C

Hexacoordinate-C

13:12

@DHMO I don't understand your question. @paracresol hello

DHMO

@Hexacoordinate-C what are we talking about?

Hexacoordinate-C

I don't really know I was just reacting to a sentence of secret

paracresol

O_o

Hexacoordinate-C

Also I won't say that $Me-C^+ =O$ is a stable specie

DHMO

@Hexacoordinate-C acylium is relatively stable

yes, stable is relative

Hexacoordinate-C

13:15

Yes but depends on the conditions

In acidic conditions I am sure it is something like with aluminum trichloride but I don't know in basic condition. I won't give my hand to cut

Yes relatively, you can make two mesomer structures so quite stable

paracresol

Random internet surfing has led me to this...the most shocking possibility there ever was...

Hexacoordinate-C

Godwin point

@DHMO what was the first question ?

paracresol

13:40

Q: What metals can't aqua regia dissolve?

Aqua regia (Latin: Royal Water) is one of the strongest acids known in Chemistry, and is capable of dissolving gold and platinum. My copy of the Oxford science dictionary goes on to say (under the entry: Aqua regia) that metallic silver does not dissolve in aqua regia. It does not mention any o...

inorganic-chemistry metal

anonymous

@paracresol
Aqua regia passivates the silver surface and so the erosion stops. Remember that silver chloride is highly insoluble and forms a coating.

Ag, Pb, Hg and Cu metals form insoluble chlorides. So now you know which metals form an insoluble coating and stops aqua regia from decomposing them further.

CowperKettle

14:17

can we say "the solution absorbs at this frequency"?

since wavelength and frequency are related, I mean

DHMO

@CowperKettle the solution absorbs light waves of this frequency...

CowperKettle

okay

DHMO

I thought you use wavenumber not wavelength

M.A.R.

@anonymous I'm confident @para's not interested in an answer to his question.

orthocresol

14:32

@CowperKettle That construction is fine.

However, I think it's more common to use wavelengths to report absorption.

Especially if you're talking about UV-vis region

anonymous

@M.A.R. I see.

orthocresol

For IR you'd use wavenumbers; for NMR you'd use chemical shift, etc..

1 hour later…

DHMO

15:53

@paracresol o/

paracresol

@M.A.R. ಠ_ಠ

@DHMO \o

@anonymous M.A.R's confidence has no basis -_-

For the record, I am interested in a decent answer to that question ._.

3 hours later…

A---B

18:46

A simple question, I would like to have suggestion on good books for introduction to orgranic chemistry. The books that seems to be popular for my purpose are Organic chemistry by Morrison and Boyd, Organic chemistry by Graham Solomon ...

and Organic Chemistry As a Second Language by David Klein

Sorry i don't know how to do hyoerlinks.

Thanks for any suggestions.

Loong

fixed

Mithoron

19:17

Q: Resources for learning Chemistry

Based on various other Stack exchange site (Mandarin Chinese, Russian and German), we adapt this project here for chemistry, since it's a great idea to have all kinds of resources in one place. This is a specifically created Community Wiki which gathers resources for learning Chemistry. The list...

software reference-request books

Michael Harding

19:29

@orthocresol hey, thought I'd let you know that Oxford rejected me in the end. I did however get an offer from Durham this week, which I'm very pleased about, will probably go there.

orthocresol

@MichaelHarding :( :)

All the best! Durham is a great place too, I have an old friend studying there. (Not chemistry though..)

2 hours later…