Descaling a coffee machine (Nespresso etc)

[rajagainstthemachine]

If you do not have anything to contribute to the topic, please refrain from replying and don't be rude. Thank you.

#doublefail

laced with acidic humor I see?

#quadruplefail

[x9200]

I would expect what happens to the scale and the acids is mostly happening on the solid-liquid phases interface. True that scale is water soluble (giving right condition, for example pure water, right temperature, sufficient time) so Maneo is a bit incorrect here, but IMHO this process for what we discuss is negligible. What the acids do to the scale is formally a corrosion process. Predominantly at least. Sorry Nak.

Huzzah, somebody typed the equations for us:

http://www.thechemicalblog.co.uk/how-to ... -descaler/" onclick="window.open(this.href);return false;

CaCO3 + 2CH3COOH -> Ca(CH3COO)2 + H2O + CO2

I still think that corrosion is the predominant mechanism for most household uses if the vinegar is cleaning something that is not so alkali. Descaling would primarily be a neutralization. But in the end, vinegar cleans all by oxidation.

Corrosion is damaging of the material by chemical reaction. A common perception is that this is only about an oxidation of the metals surface but this is not correct.

Vinegar cleans the scale by reacting with its components turning them into water (well) soluble salts of respective acids. You can call it neutralization but I think with neutralization all the components would need to be dissolved in water - the concept of neutralization is about bringing a solution to a neutral "state" typically meaning some molar 1:1 acid/base equilibrium.

Vinegar does not clean the scale by oxidation. I would say vinegar cleans hardly anything by oxidation. In oxidation/reduction something has to lose/gain some electrons. Nothing like happens when citric or acetic acids react with the scale components. CaCO3 is a Ca2+ salt and after reaction with the acid it is still Ca2+. Now, if you clean with acetic acid a kettle you made dirty with metallic Na or Mg, this would be oxidation (if the metals but not oxides) but you hardly do things like this. Cleaning common iron based rust components with acetic acid may involve some oxidation processes as there may be some Fe2+ components present but this is not a trivial topic so not being an expert in this area I would not even dare to speculate too much. Generally these two acids (acetic, citric) are not really oxidative acids - compare to Nitric or Hydrochloric for example.

[nakatago]

Vinegar cleans the scale by reacting with its components turning them into water (well) soluble salts of respective acids. You can call it neutralization but I think with neutralization all the components would need to be dissolved in water - the concept of neutralization is about bringing a solution to a neutral "state" typically meaning some molar 1:1 acid/base equilibrium.

Vinegar does not clean the scale by oxidation. I would say vinegar cleans hardly anything by oxidation. In oxidation/reduction something has to lose/gain some electrons. Nothing like happens when citric or acetic acids react with the scale components. CaCO3 is a Ca2+ salt and after reaction with the acid it is still Ca2+. Now, if you clean with acetic acid a kettle you made dirty with metallic Na or Mg, this would be oxidation (if the metals but not oxides) but you hardly do things like this. Cleaning common iron based rust components with acetic acid may involve some oxidation processes as there may be some Fe2+ components present but this is not a trivial topic so not being an expert in this area I would not even dare to speculate too much. Generally these two acids (acetic, citric) are not really oxidative acids - compare to Nitric or Hydrochloric for example.

How else would you describe breaking the CaCO3 into its ions so that it will be dissolved in the water part of a vinegar solution? I'm not describing oxidation with a weak acid as something as drastic was what nitric or hydrochloric would do.

The bond between Ca2+ and CO32- has to be broken somehow faster than simply dissolving it in water so vinegar's acidity is definitely helping out. Would it suffice to say that the H+ ions of the acid are helping that out? I saw an article from a reputed (heehee; but no, really. It's legit) source describing vinegar charges what needs to be dissolved so maybe that's the best way to describe the mechanism of how vinegar cleans things.

EDIT: I brushed up on my terminologies. Oxidation is not the best way to describe what's going on. I say it's an acid base reaction. You get the H+ from vinegar to break up the CaCO3. Then you end up with Ca2+, CO32- and CH3COO- floating around there with water and carbon dioxide.

I don't want to use corrosion because the technical definitions for corrosion is mostly concerned with metals.

(also, posts no longer say when I edited stuff and how many times I did it)

[ecureilx]

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So is vinegar better than citric acid, chemically speaking ?

I mean seriously ...

[nakatago]

...

So is vinegar better than citric acid, chemically speaking ?

I mean seriously ...

Not sure but I think the recommendations for vinegar is mostly because it's more readily available (remember how x9200 said getting some citric acid could be an issue). Sure, you can get citric acid from citrus, but then you also got some juice (sugar, oils, etc) in there as well. In a way, vinegar is purer as an acid that citrus juice.

[ecureilx]

...

So is vinegar better than citric acid, chemically speaking ?

I mean seriously ...

Not sure but I think the recommendations for vinegar is mostly because it's more readily available (remember how x9200 said getting some citric acid could be an issue). Sure, you can get citric acid from citrus, but then you also got some juice (sugar, oils, etc) in there as well. In a way, vinegar is purer as an acid that citrus juice.

Vinegar it is then ..

Datu puti.. here I come ..

[x9200]

How else would you describe breaking the CaCO3 into its ions so that it will be dissolved in the water part of a vinegar solution? I'm not describing oxidation with a weak acid as something as drastic was what nitric or hydrochloric would do.

An exchange reaction. It is an equilibrium reaction unless something happens to one of its sides that shifts the product/reagents ratio. See below.

The bond between Ca2+ and CO32- has to be broken somehow faster than simply dissolving it in water so vinegar's acidity is definitely helping out. Would it suffice to say that the H+ ions of the acid are helping that out? I saw an article from a reputed (heehee; but no, really. It's legit) source describing vinegar charges what needs to be dissolved so maybe that's the best way to describe the mechanism of how vinegar cleans things.

Not that simple. You have a lot of processes going on. You can start by realizing how complex it is to dissolve (physically) anything. I will simplify it otherwise it would kill me going into all the details.
Say, in water, a water molecules needs to have some energy, typically it is thermal energy so they don't sit there waiting but move randomly (Brownian motion). Higher temperature, more energy, more rapid (amplitude, frequency) molecular movements.

Now, why something is solid? Because there are intermolecular forces (physical or chemical bonds) holding the molecules together, strong enough so they have very limited movement (as opposite to liquids). They can be a part of a crystal network holding them even stronger. Only physical bonds can be destroyed with solvents.

To dissolve something solid water needs to break these intermolecular bond and if it has enough energy it may just kick the molecule(s) out of the solid surface but this is only a part of the puzzle. If this was only about kicking the molecule out this very molecule after some time would be kicked back to the surface (just random, diffusion based process) and get reunited with its own kind via the said bonds. To keep it in water, water needs to prevent somehow this molecule to return to his solid friends and water (solvents) can do it by creating its own bonds with the molecule. Now it is all about who is stronger. If water is not able to create effectively stronger, more stable bonds with the component it tries to dissolve then it will sooner or later land back where it came from. CaCO3 is this type of guy water have problems with so the solubility is very low.

Chemical reactions in their very simplified form occur when two molecules get closer to each other, form an intermediate state and then separate as new entities. Brownian motion component is also present as overall neutral molecules (including pairs of solvated ions) will not attract each other. For this type of acid in solution there is an equilibrium so for this very short reaction path if no other factors play part (here they do) not much would be happening except some perpetual exchange of ions.

To make it more complex the environment takes active part in all this mess so water or some water based ions can help to accelerate (or just opposite ) the reaction.
Frankly I don't know precisely how it is in case of water, acetic acid and calcium carbonate but for sure it is not that simple as you could see it from the equation. Probably it is something over this line: acetic acid anion (AAA) is thrown towards peacefully resting molecule of calcium carbonate. It may have higher affinity towards Ca2+ cation so it simply replaces the carbonic acid anion (CAA) but may actually not (sorry, I am too lazy to check this out) because for such reactions it is all about the equilibrium – CAA is not stable and it decomposes to CO2 and water. CO2 leaves the reaction environment so this equilibrium is shifted and the environment can accommodate more CAA as it is produced in exchange with AAA.

Now, on phenomenological ground as CaCO3 is not that well water soluble I would assume this process is slow as it is primary driven by diffusion (must be enough water to take one molecule away from the solid part and keep it away). The highest concentration of CaCO3 is at its sold surface and as the products of the reactions with AAA are easily water dissolved - they are quickly removed revealing fresh CaCO3 surface (faster process than CaCO3 dissolution for sure). What could stop AAA from attacking the surface would be excess of CA but CA is not stable and quickly decomposes to water CO2.

(there could be different mechanism than the "kicking out" process, but I just had to simplify it)

[x9200]

...

So is vinegar better than citric acid, chemically speaking ?

I mean seriously ...

Depends how you define better. It's less smelly and it is not voitile. These are probably the main advantages I could consider for the domestic application we are talking about.

[maneo]

...

FYI, I have a degree in chemistry.

Glad to see that you have been rewarded for your hard work.

Actually, for scale, it works by neutralizing the resulting alkali solution from the mineral deposits in hard water (and detergent residue), usually calcium compounds.

The corrosion works on everything else.

Neutralisation by a weak acid like vinegar might be relevant for preventing "scale."
However, when PUB water is boiled the more soluble bicarbonate form becomes the almost insoluble carbonate form precipitating out as solid "scale."

The original point about cleaning is for dealing with this resulting solid precipitate.
In cleaning this precipitated scale, the acid reacts with the solid, breaking it up into highly soluble ions that then can be rinsed away.

I would expect what happens to the scale and the acids is mostly happening on the solid-liquid phases interface. True that scale is water soluble (giving right condition, for example pure water, right temperature, sufficient time) so Maneo is a bit incorrect here, but IMHO this process for what we discuss is negligible. What the acids do to the scale is formally a corrosion process. Predominantly at least. Sorry Nak.

Apologies for being cavalier about the term "insoluble."
Given that the scale (likely CaCO3 as calcite) has a solubility of only 6 ppm (0.6 mg/100 g H2O) I considered it practically insoluble.
I guess I should have said "almost insoluble" or "negligibly soluble."

[x9200]

Apologies for being cavalier about the term "insoluble."
Given that the scale (likely CaCO3 as calcite) has a solubility of only 6 ppm (0.6 mg/100 g H2O) I considered it practically insoluble.
I guess I should have said "almost insoluble" or "negligibly soluble."

No worry. I did not try to be a purist. Nak raised this point of the reaction in liquid phase and even if the solubility is very low the dissolution process will progress if what is already dissolved is removed (e.g. reacting with acetic acid) so I felt it should be corrected.

[nakatago]

...

FYI, I have a degree in chemistry.

Glad to see that you have been rewarded for your hard work.

I wished.

[maneo]

So is vinegar better than citric acid, chemically speaking ?

I mean seriously ...

Not sure but I think the recommendations for vinegar is mostly because it's more readily available (remember how x9200 said getting some citric acid could be an issue). Sure, you can get citric acid from citrus, but then you also got some juice (sugar, oils, etc) in there as well. In a way, vinegar is purer as an acid that citrus juice.

Normally have just black vinegar (e.g. Zhengjiang cu), but have always had lime juice.
Lime juice might be OK for a water kettle or hot pot, but you would need to rinse more thoroughly.
However, would not recommend this for an espresso machine.

[x9200]

I would not use black vinegar. It may contain sugars (e.g. malt) and other ingredients that may decompose or precipitate in the heat exchanger/steam generator of the coffee machine and stick to its walls.

If one wants to be sure, take a table spoon (stainless steel made), pour 1-2 ml of the vinegar into it and put the spoon to an oven (convection, NOT microwave) at 150 deg C. After the liquid is evaporated keep the spoon in the oven for 5 min or so. If after this, it is possible to remove (dissolve) any sediment/stains present just by flushing it with warm water, then it is probably safe to use it. Of course if no sediment at all, then even better.

[nakatago]

I would not use black vinegar. It may contain sugars (e.g. malt) and other ingredients that may decompose or precipitate in the heat exchanger/steam generator of the coffee machine and stick to its walls.

If one wants to be sure, take a table spoon (stainless steel made), pour 1-2 ml of the vinegar into it and put the spoon to an oven (convection, NOT microwave) at 150 deg C. After the liquid is evaporated keep the spoon in the oven for 5 min or so. If after this, it is possible to remove (dissolve) any sediment/stains present just by flushing it with warm water, then it is probably safe to use it. Of course if no sediment at all, then even better.

What he said.

Or just keep a stock of white vinegar since it'll be the most useful kitchen you'll have: http://www.rd.com/home/150-household-uses-for-vinegar/" onclick="window.open(this.href);return false;
http://www.versatilevinegar.org/usesandtips.html" onclick="window.open(this.href);return false;

[maneo]

I would not use black vinegar. It may contain sugars (e.g. malt) and other ingredients that may decompose or precipitate in the heat exchanger/steam generator of the coffee machine and stick to its walls.

Wouldn't use black vinegar for cleaning anything.
Like you say, there's too much other stuff in it.
Besides that it would be a waste of good vinegar.

Found out that white vinegar was not so "readily available" here (when I went looking for it to use in a water feature to prevent slime). However, have since discovered that Mustafa's has quite a selection, especially for the cheaper artificial vinegar.
Now I keep white vinegar handy just for cleaning things.