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View Full Version : Kinda of off Topic, Need a chemist. Vinegar and salt mix


Hobster
08/10/2017, 01:03 PM
I have scoured the internet and get all kinds of conflicting information.

The question is (for cleaning brass/copper)

Mixing regular vinegar (5%acetic acid) with common table salt does speed up the cleaning reaction.

The discussion is: does it really produce HCL?? Even if it does, can it be any stronger (acid) than the original acetic acid,?

I have read that the salt is just a catalyst

The solution would be 1 cup of vinegar, 1 tablespoon salt and water to make one gal.

Thanks for any assistance.

mcgyvr
08/10/2017, 02:13 PM
Not a chemist but I put salt on my salad with vinaigrette dressing all the time :)
<---Straight up HCL eating rebel here

Hobster
08/10/2017, 03:31 PM
Not a chemist but I put salt on my salad with vinaigrette dressing all the time :)
<---Straight up HCL eating rebel here

Ya but do you eat salt and vinegar chips?:eek:

Sk8r
08/10/2017, 03:49 PM
What I used to clean copper, when I had copper---was vinegar and baking soda. From wonderopolis. "When vinegar and baking soda are first mixed together, hydrogen ions in the vinegar react with the sodium and bicarbonate ions in the baking soda. The result of this initial reaction is two new chemicals: carbonic acid and sodium acetate.
The second reaction is a decomposition reaction. The carbonic acid formed as a result of the first reaction immediately begins to decompose into water and carbon dioxide gas. "

Hobster
08/10/2017, 05:37 PM
What I used to clean copper, when I had copper---was vinegar and baking soda. From wonderopolis. "When vinegar and baking soda are first mixed together, hydrogen ions in the vinegar react with the sodium and bicarbonate ions in the baking soda. The result of this initial reaction is two new chemicals: carbonic acid and sodium acetate.
The second reaction is a decomposition reaction. The carbonic acid formed as a result of the first reaction immediately begins to decompose into water and carbon dioxide gas. "


Yes to clean silver (Wife's Jewelry) we use Vinegar baking soda and aluminum foil. Kinda of a electrolysis thing going on.

What I am trying to find a definitive answer or equation to is the reaction of vinegar and salt, does it indeed create HCL,?? I do not believe a stronger acid from 5% acetic acid can be made simply by adding salt. It is so dilute to begin with.

Some folks claim it to be harmful to brass, I dispute that.

I have some of my Mothers copper bottom pots and pans well over 50 maybe 60 years old. All that was ever used to clean the bottom was vinegar (or lemon juice) and salt.

Heck I use Randys 10-1 water to muriatic acid for clean pumps and other internal tank accessories.

bull shark
08/10/2017, 08:49 PM
HCL is formed:

NaCl+CH3COOH<->CH3COONa+HCl

The HCl and vinegar react with the copper oxide.

The NaCl is not a catalyst since it is dissolved.

bull shark
08/10/2017, 09:01 PM
The copper oxide rxns:

CuO+CH3COOH->2H20+Cu(C2H3O2)2

CuO+2HCl->H2O+CuCl

pisanoal
08/10/2017, 09:16 PM
HCL is formed:

NaCl+CH3COOH<->CH3COONa+HCl

The HCl and vinegar react with the copper oxide.

The NaCl is not a catalyst since it is dissolved.


Yes and no. Being a strong acid. Any HCl "formed" will be completely dissociated, much like the nacl and the sodium acetate. You aren't really making hcl, but any of the acetic acid molecules that dissociate are creating free hydrogen ions.

You could argue that there is an equilibrium between hcl forming and breaking apart (which is heavily weighted towards the free ion side so much so that any hcl molecules are generally considered negligible), as well as the dissociation equilibrium of acetic acid, but from a practical sense it makes no difference. The amount of free hydrogen ions, and therefore the pH is the same whether hcl is created or not.

bull shark
08/10/2017, 10:10 PM
"Formed" was inartfully written. I should have added "+" and "-" superscripts to indicate H+ and Cl- but I have no idea how to superscript in these message boxes.

Hobster
08/11/2017, 05:54 AM
Yes and no. Being a strong acid. Any HCl "formed" will be completely dissociated, much like the nacl and the sodium acetate. You aren't really making hcl, but any of the acetic acid molecules that dissociate are creating free hydrogen ions.

You could argue that there is an equilibrium between hcl forming and breaking apart (which is heavily weighted towards the free ion side so much so that any hcl molecules are generally considered negligible), as well as the dissociation equilibrium of acetic acid, but from a practical sense it makes no difference. The amount of free hydrogen ions, and therefore the pH is the same whether hcl is created or not.


Well now you guys are taking "chemistry":spin1:

What does that all mean to us mere mortals?:lol2:

Is the HCL (if "formed") insignificant??

pisanoal
08/11/2017, 08:35 AM
Well now you guys are taking "chemistry":spin1:

What does that all mean to us mere mortals?:lol2:

Is the HCL (if "formed") insignificant??

Short answer, yes.

If you are interested in the specifics, keep reading.


The somewhat simple definition of an acid is a molecule that has a hydrogen ion that will separate from the molecule with the addition of water. Or, a compound that when added to water, will lower the pH.

pH is the measure of the concentration of free hydrogen ions.

There are strong acids and weak acids. A strong acid completely dissociates (breaks apart into constituent ions i.e. HCl becomes H+ and Cl-) in water. Meaning if I add 10 parts HCl to water, I have 10 parts free hydrogen ions that are effecting pH.

A weak acid is an acid that does not completely dissociate. It forms an equilibrium reaction, meaning as quickly as its breaking apart, it is reforming. What that means is the parts of free hydrogen that is formed is not equal to the amount of weak acid (in this case, acetic acid). It is calculated using a known equilibrium constant, and is some portion of the whole amount of weak acid.

So in your case, you have a sodium chloride solution which has sodium ions and chloride ions floating around. You add acetic acid, a weak acid, which has one hydrogen that will dissociate from it. That dissociation reaction will reach equilibrium at some percentage of the amount of acetic acid you add. You will have a double replacement reaction going on as well that will form sodium acetate and hydrogen chloride. However, those reactions are so heavily favored towards dissociation that it is negligible in terms of its effect on pH.

Summary of all of that is the pH of your solution is controlled by the amount of acetic acid you add. There may be a minor effect of sodium chloride on the pH, but it would be insignificant.

pisanoal
08/11/2017, 08:40 AM
"Formed" was inartfully written. I should have added "+" and "-" superscripts to indicate H+ and Cl- but I have no idea how to superscript in these message boxes.

I didn't mean to pick your post apart. What you said about NaCl not being a catalyst at the end made it clear you already understood what I had went on to say. I just wanted to clarify for the OP that the HCl in your equation was not adding any acidity to the solution.

Hobster
08/11/2017, 09:20 AM
Short answer, yes.

If you are interested in the specifics, keep reading.


The somewhat simple definition of an acid is a molecule that has a hydrogen ion that will separate from the molecule with the addition of water. Or, a compound that when added to water, will lower the pH.

pH is the measure of the concentration of free hydrogen ions.

There are strong acids and weak acids. A strong acid completely dissociates (breaks apart into constituent ions i.e. HCl becomes H+ and Cl-) in water. Meaning if I add 10 parts HCl to water, I have 10 parts free hydrogen ions that are effecting pH.

A weak acid is an acid that does not completely dissociate. It forms an equilibrium reaction, meaning as quickly as its breaking apart, it is reforming. What that means is the parts of free hydrogen that is formed is not equal to the amount of weak acid (in this case, acetic acid). It is calculated using a known equilibrium constant, and is some portion of the whole amount of weak acid.

So in your case, you have a sodium chloride solution which has sodium ions and chloride ions floating around. You add acetic acid, a weak acid, which has one hydrogen that will dissociate from it. That dissociation reaction will reach equilibrium at some percentage of the amount of acetic acid you add. You will have a double replacement reaction going on as well that will form sodium acetate and hydrogen chloride. However, those reactions are so heavily favored towards dissociation that it is negligible in terms of its effect on pH.

Summary of all of that is the pH of your solution is controlled by the amount of acetic acid you add. There may be a minor effect of sodium chloride on the pH, but it would be insignificant.

Thank you for the explanation although I admit most of it is beyond my basic chemistry knowledge.

So just to summarize. When you say short answer "yes" that is, the HCL is insignificant.

and

The reaction or whatever is formed is not any "stronger" than the initial 5% acetic acid?

My pH meter probe is no longer good so I can not actually test the pH

The bottom line of all this is some folks claim this mixture will damage brass or leach out the zinc. My "belief" is it doesn't, and would depend on the amount of time the brass is exposed to the solution and of course the percentage of the mix. To me 1 cup of 5% Vinegar and some salt is not going to damage to brass in say 15 to 30 minutes.

Side note:

I have had boats/motors in saltwater for years and know of electrolysis and the old copper based anti fouling paints, Brass fittings under water lasted forever. Sacrificial zincs on outboard motors (alloys) last for a long time before corroding.

pisanoal
08/11/2017, 11:41 AM
Thank you for the explanation although I admit most of it is beyond my basic chemistry knowledge.

So just to summarize. When you say short answer "yes" that is, the HCL is insignificant.

and

The reaction or whatever is formed is not any "stronger" than the initial 5% acetic acid?

My pH meter probe is no longer good so I can not actually test the pH

The bottom line of all this is some folks claim this mixture will damage brass or leach out the zinc. My "belief" is it doesn't, and would depend on the amount of time the brass is exposed to the solution and of course the percentage of the mix. To me 1 cup of 5% Vinegar and some salt is not going to damage to brass in say 15 to 30 minutes.

Side note:

I have had boats/motors in saltwater for years and know of electrolysis and the old copper based anti fouling paints, Brass fittings under water lasted forever. Sacrificial zincs on outboard motors (alloys) last for a long time before corroding.

Your summary of my post is correct.

I cant say for sure to the leaching of zinc, but my gut says that is not likely to be a significant issue. If you were going to leave it in there for months, maybe, but 30 minutes I wouldn't worry.

Hobster
08/11/2017, 12:16 PM
Thank you very much for you time to explain all this.:thumbsup:

I can now debate with confidence, I will not drop any names. Just bewilder them with brilliance!:lmao:

Dan_P
08/11/2017, 04:25 PM
Removing tarnish with such mild reagents work because the metal oxide or sulfide is not very thick. A paste of sodium chloride or sodium bicarbonate are sufficient to polish the surface.The acetic acid is probably just a liquid to make the paste. It might dissolve copper oxides. You'll note that a mixture of vinegar and a lot of baking soda is really just a paste of baking soda and sodium acetate. No acid at all is needed! I am tempted to try a paste of sodium chloride and water.

Mr. Wiggles
08/11/2017, 08:36 PM
HCL is formed:

NaCl+CH3COOH<->CH3COONa+HCl

The HCl and vinegar react with the copper oxide.

The NaCl is not a catalyst since it is dissolved.

Sorry but I completely disagree. HCl is not formed in this reaction at all, it simply isn't possible. The acetate is a buffer and wouldn't allow the pH to be low enough to form HCl, and the pKa are different by about 12 units. Also this business about NaCl as a catalyst makes no sense whatsoever. Whether or not it is in solution makes no difference to a catalyst. A catalyst isn't consumed in a reaction by definition and the NaCl it isn't changing the energy barrier for a reaction.

Not trying to be a jerk about this, I just want to set things straight. I have a Ph.D in chemistry so these types of discussions are interesting to me and I don't want folks to be propagating misinformation.

I hope that helps!

bertoni
08/11/2017, 09:03 PM
Sorry but I completely disagree. HCl is not formed in this reaction at all, it simply isn't possible.
I agree. This topic has come up a lot. The H<sup>+</sup> and other ions are all in solution, and it's meaningless to talk about them combining into new forms as mentioned. The acetate will still be there, interfering with the pH, as has been stated.

The vinegar won't decay in such a solution at much of any rate unless the vinegar is diluted or neutralized. Vinegar is toxic to microbes at high enough concentrations, which is why vinegar is shelf stable.

Mr. Wiggles
08/12/2017, 05:44 AM
Removing tarnish with such mild reagents work because the metal oxide or sulfide is not very thick. A paste of sodium chloride or sodium bicarbonate are sufficient to polish the surface.The acetic acid is probably just a liquid to make the paste. It might dissolve copper oxides. You'll note that a mixture of vinegar and a lot of baking soda is really just a paste of baking soda and sodium acetate. No acid at all is needed! I am tempted to try a paste of sodium chloride and water.

This is probably the closest post to being correct on the metal polishing here. The salt or bicarbonate is really just acting as a mild abrasive that won't scratch the copper or silver surface. The acid is providing some liquid to make a paste and some acidity to help remove the oxide layers.

Hobster
08/12/2017, 07:05 AM
Sorry but I completely disagree. HCl is not formed in this reaction at all, it simply isn't possible. The acetate is a buffer and wouldn't allow the pH to be low enough to form HCl, and the pKa are different by about 12 units. Also this business about NaCl as a catalyst makes no sense whatsoever. Whether or not it is in solution makes no difference to a catalyst. A catalyst isn't consumed in a reaction by definition and the NaCl it isn't changing the energy barrier for a reaction.

Not trying to be a jerk about this, I just want to set things straight. I have a Ph.D in chemistry so these types of discussions are interesting to me and I don't want folks to be propagating misinformation.

I hope that helps!

This is exactly why I mentioned previously that I had searched and searched the web for information.

Everything I found was yes, no, sort of and sometimes maybe.:mixed:

Mr. Wiggles
08/12/2017, 08:14 AM
No problem, chemistry isn't always the easiest subject. But I see a lot of misinformation posted online so I wanted to make sure that it is clear that the answer is no. :spin1: