Potassium Carbonate + Ascorbic Acid reaction

[Athiril]

Being a theoretical chemistry newb, I was wondering to what ratio per gram do I add potassium carbonate to ascorbic acid to have total conversion to potassium ascorbate?

And how many grams do I get of potassium ascorbate?

 

[Alan Johnson]

K2C03 +.......... 2C6H8O6.....->2KC6H7O6........+H2O...+CO2
Pot Carbonate..Ascorbic Acid ...Pot Ascorbate...Water..Carbon Dioxide
138.2g............2x176.1g.........2x214.2g...........18g.....44g
138.2g+..........352.2g.........->428.4g............+18g....+44g
ie mixing 138.2grams potassium carbonate and 352.2 grams ascorbic acid gives 428.4 grams potassium ascorbate.
Unusual chemical,wonder what that is for.

 

[Photo Engineer]

There is more than one acid group on Ascorbic acid. Tell us how many you want to neutralize before we tell you how much carbonate. The formula above is correct for ONE acid group.

PE

 

[Alan Johnson]

In food additives, E300 is ascorbic acid, E301 is sodium ascorbate, E302 is calcium ascorbate and E303 is potassium ascorbate KC6H7O6 cas 15421 15 5 and I'm guessing that is the common form of potassium ascorbate.It is analogous to sodium ascorbate used in photochemicals.

 

[Athiril]

I assume its L-Ascorbic Acid, got it from the health food store, no infon on packet or wesite apart from it being pure ascorbic acid.

 

[Photo Engineer]

That does not tell us whether you want the mono Sodium or a higher number. We can assume one, and then Alan's post is correct.

PE

 

[Athiril]

Sodium? Alan is correct in assuming I just want the common form (E303), the ascorbates are the same price per gram as ascorbic acid here.

 

[Photo Engineer]

The Sodium and Potassium salts are equivalent in activity when adjusted for the molecular weights of the two metal ions. In Europe, K is more prevalent and slightly less expensive but in the US, Na is more prevalent and less expensive. I guess the world's supply of Na and K is lopsided.



PE

 

[Murray Kelly]

The Sodium and Potassium salts are equivalent in activity when adjusted for the molecular weights of the two metal ions. In Europe, K is more prevalent and slightly less expensive but in the US, Na is more prevalent and less expensive. I guess the world's supply of Na and K is lopsided.



PE

I have never seen a really convincing explanation of why potassium (K) salts were easier (cheaper?) to get then sodium (Natrium) salts to the old German chemists. A bit O/T I know, but it troubles me.

To answer the original question - would one add carbonate until the fizzing stops, like converting AA to Na ascorbate with sod. bicarbonate?
Murray

 

[Photo Engineer]

You might add until the fizzing stops, but that does not tell you what point in the equillibrium you are at. You see, CO2 dissolves in water, so some of it does not "fizz off", and due to having more than one acid group, each one weaker than the one before, you reach a point where there are still some acid groups hanging around that won't cause fizzing. So, molecular weight is the best way to "neutralize" a weak acid with a weak base.

PE

 

[H2O]

There is more than one acid group on Ascorbic acid. Tell us how many you want to neutralize before we tell you how much carbonate. The formula above is correct for ONE acid group.

PE

Ascorbic acid has not typical acid group for organic acids (carboxyl group, -COOH) Yes, for axample, citric acid has 3 carboxyl group and can be neutralized in 3 steps [pK(a1)=3,2; pK(a2)=4,8; pK(a3)=6,4] (approx.)
AA has several hydroxyl groups in "enol" configuration and they are strong acid. Molecule behaves as monohydric acid [pK(a)=4,0]!

 

[Photo Engineer]

Ascorbic acid effectively has 2 acid groups that can be neutralized, although only neutralizing one is most common. It is a complex sugar acid that exists in a variety of forms.

PE

 

[Athiril]

I have both sodium and potassium carbonate, potassium is slightly more expensive and not available at supermarkets, I chose the potassium, as I was under the impression I can dissolve more potassium salts in water than sodium?

 

[Photo Engineer]

That is generally correct.

PE

 

[Kirk Keyes]

I have never seen a really convincing explanation of why potassium (K) salts were easier (cheaper?) to get then sodium (Natrium) salts to the old German chemists. A bit O/T I know, but it troubles me.

It is an interesting question!

Historically, potash, which is primarily potassium carbonate, was and still is used are a basic chemical starting point. It also contains a fair amount of potassium chloride, it can be converted into potassium hydroxide, and reacted with other chemicals to form potassium nitrate and potassium sulfate as well. The potassium nitrate and sulfate were commonly used as fertillizers. From these compounds, many other chemicals and products can be made, a few being using to make soaps, glass, ceramics, chemical dyes, drugs, and synthetic rubber.

So what does this have to do with the prevalence of potassium salts in Europe? There are relatively large potash resources in Germany and this availability of a basic chemical building blocks is partially why Germany became such a world leader in chemical production during the 20th Century.

There was quite a problem with the USA chemical industry during WWI as the supply of potash from Germany was cut off. During WWI, it was found that potash could be made in the USA as a by-product from Portland Cement manufacturing and it was realized that this discovery could make the USA forever free from Germany's potash supply. This ended up being only one sources of potash in the USA - salt brines from dry lake deposits in the deserts of the US West, ashing of kelp and other plants (i.e. trees - the first patent in given in the USA was for an improved potash production process using tree ash), and as a byproduct of steel, beet sugar, and molasses production.

So back to the original question - why the prevalence of sodium compounds in the USA? Even with the possible sources of potash I listed available in the USA at the end of WWI, there were relatively few sources of sodium salts in the USA at that time. Soda ash, the sodium equivalent to potash, was primarily produced in the USA in 1900 using the Solvay Process. Also known as the ammonia-soda process, it was invented in the 1860s and used ammonia, salt brine, and carbon dioxide to form soda ash.

It was discovered that there were large surface and huge underground deposits in the Western USA states of California, Nevada, and Wyoming. Today, all commercial sources of soda ash in the USA are from natural deposits. (Interestingly, the Solvay process was abandoned in one of those rare instances where naturally occuring soda ash ended up being more easily mined than made synthetically as opposed to a natural product being replaced by a synthetic one.)

Soda ash is used as a basic chemical resource, just as is potash. Additionally, production of soda ash far exceeded the production of potash in the USA as the 20th Century progressed.

So with this large source of soda ash available in the USA, it's not surprising that the bulk of raw chemicals in the USA are produced with sodium and not potassium.

 

[Murray Kelly]

Thank you, Kirk.
Murray

 

[Murray Kelly]

PE - Ron, unlike yourself I am neither a chemist nor an engineer. So, I would in fact, add just that bit more to be sure to be sure the fizzing had stopped.
There's the possibility that 1.5g/l of CO2 would have been dissolved at the exact neutralisation point but more bicarbonate would raise the pH from that point quite quickly? The CO2 (as H2CO3) would give up the inequal struggle and fizz or turn the bicarb into plain carbonate..
With a pH of 5.6 and 1.5g/l I'd bet the alkali of the final developer would handle his homebrew soup CO2, quick, smart.
Oh, and you've already told us you have to decide which Acid radicals you want to neutralise, so there must be different amts of carbonate / bicarbonate to calculate? I apologise if I have the terminology wrong.
Murray

You might add until the fizzing stops, but that does not tell you what point in the equillibrium you are at. You see, CO2 dissolves in water, so some of it does not "fizz off", and due to having more than one acid group, each one weaker than the one before, you reach a point where there are still some acid groups hanging around that won't cause fizzing. So, molecular weight is the best way to "neutralize" a weak acid with a weak base.

PE

 

[Photo Engineer]

Well, the only sure way is to raise the pH to a testable value either with pH paper or with an inexpensive pH meter. You can buy Hanna pocket meters for about $80 US. Or you can get pH paper with the range and accuracy you want for about $20 US for 100 strips. I use both. These methods are more sure than guess and by golly! Otherwise, your results will even vary with the air pressure and ambient temperature if you use the fizz method.

PE

 

[Murray Kelly]

At last we agree on something I have a cheap pH meter and I do exactly what you say - I add the little extra bicarb to be sure the pH is up. It is, after all, going into a brew with a fairly strong alkali .
Mostly the atmospheric pressure is 1 Bar +- 1% and the house temp 23-25 C.
I checked the tables and the CO2 doesn't vary much in solubility over that range.
Murray

 

[Photo Engineer]

Murray;

Regarding the tables, here is something interesting from an article entitled "Rea-Time Observation of Carbonic Acid Formation in Aqueous Solution" by Adamczyk et. al. Science, Dec. 2009, p1690.

"Despite the widespread importance of aqueous bicarbonate chemistry, its conjugate acid, carbonic acid, has remained uncharacterized in solution...."

Just goes to show you how much we do know. That is why actual measurement is so important. Interesting article BTW, but not too terribly important here, except to show how little we know with exactitude.

PE

 

[dancqu]

Neutralization

You might add until the fizzing stops, but that does not tell
you what point in the equillibrium you are at.
PE

Potassium ascorbate is the potassium salt of a weak acid.
As both chemicals are diprotic combining them in proportion
to their gram formula weights will result in a neutralization.

Perhaps Ron knows of the ph at that neutralization and of the
ph of a solution of potassium ascorbate. I believe they
will differ but both be alkaline. Dan

 

[Photo Engineer]

I don't offhand. No. Perhaps you can supply them from your store of data. I've gotten about 10 messages on this and other subjects today and over the last 2 days and I've gotten a bit tired. I want to relax for a while. Sorry.

PE

 

[H2O]

Ascorbic acid effectively has 2 acid groups that can be neutralized...

OK, but it depends on neutralizing agent (or medium). Acidity (alkality) is relatively term.
Some acid is acid in one medium and the same acid can be alkali in another medium. Very roughly spoken.
Ascorbic acid has effectively 2 acid groups in potassium hydroxide not in medium of potassium carbonate.
Potassium carbonate is weaker alkali than potassium hydroxide.
Potassium carbonate is alkalii for the first step of neutralization of ascorbic acid, but is not good alkali for stechiometric the second step of neutralization of ascorbic acid.
I think that equation from Alan Johnson si correct. Only one step to monoascorbate.
Monopotassium ascorbate doesn't react with potassium carbonate to form carbon dioxide (and dipotassium ascorbate).

 

[Photo Engineer]

I said that Alan was correct and I also agree with you. OTOH, it is easy to miss your aim point without weighing materials and even then the equillibrium is not 100% nor are the weights necessarily correct due to hydration.

I maintain that the best way to do this is to aim for a target pH and use some form of measurement to achieve this aim point. Otherwise, the results are inexact. This is especially true as carbonate picks up water from the air. See the article in Dec 2009 Science on carbonic acid.

PE

 

[H2O]

I know what was said, but:

That does not tell us whether you want the mono Sodium or a higher number. We can assume one, and then Alan's post is correct.PE

In case of neutralization of ascorbic acid by carbonate (K or Na) is useless to talk about higher number neutralization or about more that one step of neutralization.