Citrates

[Sapo]

Just thought I'd throw it out there, not really sure if it makes any difference or not, more of a technicallity I guess. But if Dunn is right, then we are wrong:

When it comes to liquid soap, the reaction between potassium hydroxide and citric acid doesn't technically yield potassium citrate. Quote (page 159): "Potassium and citrate ions remain floating around in solution and come together only if the water is boiled away, leaving the salt potassium citrate."

Meanwhile in bars we probably actually do get sodium citrate, since most of the water is evaporated.

I suppose if the potassium/sodium citrate has better chelating abilities than citrate alone, the "issue" becomes more relevant and not just a semantical thing. The answer to that is of course unknown to me.

PS: Loving the book so far, and I didn't even get to the good bits yet :mrgreen:. Highly recommended.

 

[DeeAnna]

It is the citrate ion that is the chelator, regardless of whether you start with potassium citrate or sodium citrate.

Don't forget the water used for washing is also a part of the soap solution that you are using to clean your skin -- you don't just wash with a dry bar of soap.

 

[topofmurrayhill]

Just thought I'd throw it out there, not really sure if it makes any difference or not, more of a technicallity I guess. But if Dunn is right, then we are wrong:

When it comes to liquid soap, the reaction between potassium hydroxide and citric acid doesn't technically yield potassium citrate. Quote (page 159): "Potassium and citrate ions remain floating around in solution and come together only if the water is boiled away, leaving the salt potassium citrate."

Meanwhile in bars we probably actually do get sodium citrate, since most of the water is evaporated.

I suppose if the potassium/sodium citrate has better chelating abilities than citrate alone, the "issue" becomes more relevant and not just a semantical thing. The answer to that is of course unknown to me.

PS: Loving the book so far, and I didn't even get to the good bits yet :mrgreen:. Highly recommended.

When salts are dissolved in water, they dissociate into positive and negative ions to a greater or lesser extent (ranging from almost not at all to pretty much completely).

The ones that dissociate to a greater extent are called strong electrolytes (so named because they enable the solution to conduct electricity). Potassium citrate would fall into that category, as would a few other things you frequently encounter such as table salt. When table salt dissolves in water, it's still a sodium chloride solution even though the ions don't get back together until the water is evaporated. Under normal circumstances you thankfully wouldn't encounter the properties of sodium metal or chlorine gas (and hence you don't drop dead when dissolving salt).

Soap itself dissociates to some extent in water. The degree to which various fatty acid salts do that is actually what determines the pH of the soap. They are all different, so it's hard to predict what pH a soap should be based on the recipe.