Sciencemadness Discussion Board

The science of cleaning coffee pots with lemon wedges, ice, and salt

biscuit_eater - 1-2-2010 at 05:14

A friend of mine recently told me how I can clean coffee stains on coffee pots by filling the coffee pot up about half way with ice cubes, lemon wedges, and about two tablespoons of salt. The instructions were to swirl the mixture of ice, lemon wedges, and salt around in the pot for a few minutes to clean the coffee pot.

This method of cleaning coffee pots effectively cleaned my coffee pot.

I looked this up on the internet, and I found that lots of people on the internet have recommended this method of cleaning coffee pots with lemon juice, ice, and salt.

I have questions about how this works chemically speaking.

I figure that the acid in the lemons helps clean the coffee pot because lemon juice or mixtures of lemon juice (or vinegar) are often given as hints on how to clean glass and other surfaces using household products.

What is the function of the ice in the lemon/ice/salt mixture? Is ice just a vehicle to carry the acid in the lemons? I mean, would liquid water work just as well as ice? I thought maybe they say to use ice rather than liquid water because perhaps the ice cubes carry more friction against the bottom of the coffee pot than liquid water would.

I think I've also read about salt water mixtures being used to clean before.

But if one already has lemon wedges and ice in the mixture, why does everyone say to add salt?

Does the salt somehow have a synergistic effect on the lemon and/or ice to make cleaning coffee pots more effective than just using lemon and ice alone?

User - 1-2-2010 at 06:28

I would declare the ice to be pure nonsense.
Reactions proceed 2 times faster for every 10 degrees C, making it colder just slows down the process.
As for lemons, well yes they are quite acidic and there for having cleaning properties.
Still using plain vinegar preferably stronger solutions would do the same job and better.
This is also due to the chalk removing/dissolving properties.
Use strong vinegar and forget lemons :)
Be sure to clean up and remove the remaining acid, that makes bad coffee.


[Edited on 1-2-2010 by User]

ScienceSquirrel - 1-2-2010 at 06:48

Lemon juice is a lot better cleaner than vinegar of an equivalent concentration.
The citric acid has a chelating effect on metal ions.
The salt acts as a mild abrasive, it is quite common to clean out bottles and barrels used for home brewed beer with some salt and cold water. A hot water rinse then gets rid of the salt.

aonomus - 1-2-2010 at 06:51

Water scale is mostly CaCO3, and is for the most part insoluble (or impreciably soluble). Vinegar contains acetic acid, while lemons contain citric acid. Calcium acetate is very soluble in water, and calcium citrate less so. I would suppose that the sodium chloride is to help with the solubility of calcium citrate somehow.

From the basics, it would appear that the vinegar would do a better job due to the higher solubility of the calcium salt.

crazyboy - 1-2-2010 at 07:12

I suspect the ice might prevent the salt from dissolving in the water so it acts as an abrasive. The mild acid of the lemon juice could help attack the build up.

bbartlog - 1-2-2010 at 07:35

The Cl- that the salt puts in solution may also speed dissolution of some stuff (carbonates, oxides). When cleaning pennies with vinegar, salt is added for this reason; I don't think it changes the net stoichiometry in any way (obviously the Cl is going to stick with the Na) but it can aid in the formation of intermediates that change the rate of reaction.
I also wouldn't discount the possibility that limonene or other oils from the rinds of the lemon wedges play some part in the cleaning. Not that there's going to be a whole lot of limonene nor does it sound like this would be a particularly good way to release it, but it's quite a good cleaning agent for some things (like other oils).

unionised - 1-2-2010 at 13:45

I suspect the ice is there to act as "lumps of stuff" that bash the lemon/salt mixture against the walls of the teapot.

bbartlog - 1-2-2010 at 14:09

Another possible role for ice in the pot would be to change the preferred location of precipitate formation in the system. If you have a hot liquid in a coffeepot, any substance that's more soluble in hot than cold water (which is most of them) will tend to come out of solution on the coldest surface, that is, the walls of the pot. If you have ice cubes in the water, then the warmest place in the system would be the walls of the pot and any cycle of dissolution and precipitation would be from the walls to the ice cubes (or near them).

FrankRizzo - 1-2-2010 at 16:48

aonomus is right. Stains are usually a result of porous insoluble calcium deposits from hard water becoming stained from the coffee. The acid from the lemon juice turns the calcium compounds into soluble ones, the salt is an abrasive, and the ice acts as "scrubbies" so that the salt presses against the glass with some force.

12AX7 - 1-2-2010 at 22:57

Quote: Originally posted by bbartlog  
The Cl- that the salt puts in solution may also speed dissolution of some stuff (carbonates, oxides). When cleaning pennies with vinegar, salt is added for this reason; I don't think it changes the net stoichiometry in any way (obviously the Cl is going to stick with the Na) but it can aid in the formation of intermediates that change the rate of reaction.


That particular one works by complexing the copper. Copper chloride forms readily. Copper acetate is also a stable complex, but maybe it's not as fast (must be, the salt works before your eyes in a vinegar solution!).

Tim