Science-y thought/question

[FlybyStardancer]

This is an idea that I've had off and on for a bit now. I have no working way to test it, and I can't seem to find anything on a quick google search.

My hypothesis is that there is a link between soap hardness and the amount of sodium ions in the soap batter (from any/all sources).

It came to me because what are common additives to harden soap? Sodium chloride (table salt) and sodium lactate. Plus those superlye castiles we were playing around with last year ended up super hard (again, more sodium!).

Has anyone else noticed this? Does it make any amount of sense to anyone else? Or am I just on a crazy train?

 

[jules92207]

I'm riding the caboose to see where this crazy train takes us...

 

[Sonya-m]

Reckon we need DeeAnna to pop in!

Just thinking isn't all soap a salt anyway? Doesn't the oil and the lye form the salts of the fatty acids in the oils ie sodium cocoate etc?

 

[Susie]

Reckon we need DeeAnna to pop in!

Just thinking isn't all soap a salt anyway? Doesn't the oil and the lye form the salts of the fatty acids in the oils ie sodium cocoate etc?

We do need DeeAnna to pop in! But until then, don't confuse "salt" with sodium. A "salt" is not necessarily sodium. A salt results from an acid and a base combining, whether that base(alkaline) is made with Na(sodium), or K(potassium).

 

[Sonya-m]

We do need DeeAnna to pop in! But until then, don't confuse "salt" with sodium. A "salt" is not necessarily sodium. A salt results from an acid and a base combining, whether that base(alkaline) is made with Na(sodium), or K(potassium).

Sorry I meant for CP soap we create the salt of the fatty acids we use

All of the salts created using sodium hydroxide ie bar soap contain sodium I assume?

 

[Susie]

Yes, soap "salt" made with NaOH should have sodium in them. But, it is extremely easy for people to confuse "salt" and sodium. Especially as some soaps are made with table salt(NaCl), sea salt, dead sea salt, Himalayan pink salt, etc, etc. We just need to be really clear to folks unfamiliar with the basic chemistry behind soapmaking which "salt" we are referring to.

 

[Nehlena]

Until DeeAnna pops... this is something good to read...

http://www.chemistryexplained.com/Ru-Sp/Salt.html

and this for general salts...

http://www.infoplease.com/encyclope...und-characteristics-classification-salts.html

 

[boyago]

I think the OP was referring to the ion charges of the salts we use and possibly the ionic bonding leading toward a harder bar. I don't have the science juju to clearly understand the ionic charges of materials though or know if that influences the hardness of a material.

 

[Susie]

I know that, but this is not the first conversation I have had this week about soap "salt" vs table salt(NaCl) vs liquid soap "salt", and I just did not want to go the whole 10 rounds again by letting anyone misunderstand which salt is being referred to. I really am not trying to insult anyone, just trying to avoid that whole rigamarole again.

 

[Sonya-m]

Ah right, I didn't know there was another thread elsewhere. Hope my responses weren't confusing to anyone

 

[MorpheusPA]

Off the cuff, it makes sense. In soil chemistry, sodium will form a hard, crusty, impenetrable soil (it's also of increasing toxicity above 1%, but fortunately soap does not grow plants).

Potassium isn't as bad, and is necessary in the 2-5% range. But the ionic radius is much larger and the shielding electrons greater in number, so the bond is weaker.

Add more sodium and the attraction is strong no matter where you are as there are plenty of sodium ions hanging around to be drawn to the negatively charge end of the soap molecule. Hence, harder soap even when water levels are high.

I've noticed that, over time, soap with salt is about as hard as soap without salt as the excess water evaporates. So during curing, the hardness evens out. There's not as much water to dissolve the soap salts and they stay crystalline, I guess.

So for fast hardening soap, make sure it has a sodium excess from table salt, sodium lactate, and so on. Later on, as long as there's enough sodium to assure that lots of free fats aren't floating around, it's solid regardless.

 

[DeeAnna]

FTLooks to me like y'all are doing fine without me! You have a point about sodium ions -- Na+ -- and hardness. Like most things in life, the idea has some limits, but it's useful to know.

Talking about bar type soaps, there are two components to soap ... the solid soap framework and the liquid film within the solid framework. The liquid film contains water, ions including Na+, other dissolved materials such as sugars and such, and dissolved soap molecules.

Soap, believe it or not, is fairly insoluble when sodium ions are present. The more sodium ions in the liquid fDRilm, the less soap will be dissolved in the liquid. Instead, the soap becomes part of the solid soap framework and this acts to harden bar soap.

There are limits to this in that the short chain, saturated soaps from coconut and PKO are more soluble in the presence of Na+ ions than longer chain saturated soaps (palm, tallow, lard) and unsaturated soaps (olive and the other liquid fats).

So even though a salt soap made with CO gets really hard-like-a-rock, it lathers well. An olive soap would be a dismal failure as a salt bar because it would be hard AND be so insoluble it would not lather well. This is also partly the reason why olive liquid soaps can be thickened by adding table salt, but liquid soaps made with CO do not thicken well with table salt.

I'm not sure I'm really addressing the question directly ... I'm a bit muzzy headed right now, but I hope this is helpful.

 

[FlybyStardancer]

So are you thinking that the additional Na+ ions in the salt increase the insolubility of the soaps to make them harder?

I'm thinking to know, we'd probably have to do a bunch of crystallography... And the only way I can think of to isolate the sodium as what's causing the soaps to harden is to use pure sodium... which would not be a good idea!

 

[MorpheusPA]

So are you thinking that the additional Na+ ions in the salt increase the insolubility of the soaps to make them harder?

I'm thinking to know, we'd probably have to do a bunch of crystallography... And the only way I can think of to isolate the sodium as what's causing the soaps to harden is to use pure sodium... which would not be a good idea!

You'll get a pretty good idea by using various amounts of sodium in a given formula, then test the hardness with a formal machine. It wouldn't tell you the actual crystallization status, but would at least tell you how hard the bar actually is.

If sodium chloride and sodium lactate both harden a bar (which, in my experience, they do), then it's most likely the sodium. I've never used sodium citrate, but if that works as well, there's a third data point.

Of course, another good test would be start replacing the sodium with something else. We do that when we use KOH to make liquid soap...and the soap is definitely not as hard. So add potassium chloride instead of sodium chloride. If the resulting soap is not as hard, it's not the chloride ion doing it.

 

[SoapBro]

You'll get a pretty good idea by using various amounts of sodium in a given formula, then test the hardness with a formal machine. It wouldn't tell you the actual crystallization status, but would at least tell you how hard the bar actually is.

If sodium chloride and sodium lactate both harden a bar (which, in my experience, they do), then it's most likely the sodium. I've never used sodium citrate, but if that works as well, there's a third data point.

Of course, another good test would be start replacing the sodium with something else. We do that when we use KOH to make liquid soap...and the soap is definitely not as hard. So add potassium chloride instead of sodium chloride. If the resulting soap is not as hard, it's not the chloride ion doing it.

Regular user of sodium citrate here, although it helps with soap scum, the more sodium citrate you add the softer your bar becomes.

a 70% olive oil 30% coconut oil soap that can usually be unfolded after 24h without any difficulty without any sodium citrate becomes too soft to unmold after 24h if 3%+ (of oil weight) of sodium citrate was added to it.

i'm no chemist but from what i've read, sodium citrate is a buffering agent that among other things is used to prevent drastic shifts in PH in a solution, i dont know if this means it neutralizes some of the lye and increases the superfat or if the lye doesn't react with it at all and it just takes longer to react with the oils because the solution is somewhat buffered..

will investigate further.

 

[MorpheusPA]

The hypothesis would be invalid if sodium citrate is an acid or buffer, yes. Anything that keeps the lye from doing its thing isn't going to work in an experiment.

Er, any other sodium derivatives? Sodium carbonate, perhaps?

 

[SoapBro]

The hypothesis would be invalid if sodium citrate is an acid or buffer, yes. Anything that keeps the lye from doing its thing isn't going to work in an experiment.

Er, any other sodium derivatives? Sodium carbonate, perhaps?

trisodium citrate (the one used in food and soap) has a PH of 8, so its not really an acid..

does anyone know if the sodium citrate actually neutralize some of the lye or if they dont react and the citrate just inhibits the lye from reacting with the oils somehow?

 

[The Efficacious Gentleman]

Sodium citrate is a sodium salt of citric acid, so it won't be as reactionary with the lye as citric acid is. I won't say it doesn't react at all, but then if:

Citric acid + lye = sodium citrate

Then

Sodium citrate + lye ((should)) = sodium citrate and lye

If in the second equation anything else would come, then that should also be the case with the first equation.

 

[SoapBro]

Sodium citrate is a sodium salt of citric acid, so it won't be as reactionary with the lye as citric acid is. I won't say it doesn't react at all, but then if:

Citric acid + lye = sodium citrate

Then

Sodium citrate + lye ((should)) = sodium citrate and lye

If in the second equation anything else would come, then that should also be the case with the first equation.

Thats what i also thought, since sodium citrate is the product of citric acid + lye then combining sodium citrate with lye should not react, but then how do you explain the soap getting softer when adding sodium citrate to the mix?

 

[DeeAnna]

"...the additional Na+ ions in the salt increase the insolubility of the soaps to make them harder?..."

Yes, that's what I'm thinking.

"...If sodium chloride and sodium lactate both harden a bar (which, in my experience, they do), then it's most likely the sodium...."
"...the more sodium citrate you add the softer your bar becomes...."

I will also add that sodium lactate will soften a bar if too much is added. I don't have personal experience with sodium lactate in bar soap, but I use it in my liquid soap. I have read posts by experienced soapers who report sodium lactate above about 3% ppo actually softens the soap.

I want to remind you all that some ionic molecules do not fully dissociate when dissolved in a liquid. Depending on the pH and the other chemicals in solution, these ionic molecules may remain fully intact, some may partly dissociate (break apart into their electrically charged ionic components) and some may remain as intact molecules. To us humans, a big effect of these types of ionic chemicals is they stabilize pH -- they keep the pH about the same. In the lingo of the chemist, these chemicals are buffers.

Table salt (sodium chloride) dissociates pretty much completely and is not a buffer. Sodium citrate is a buffer. Sodium lactate is a buffer. Soap is a buffer. Tread carefully when dealing with a complex mix of buffers -- the results you get are not likely to be what "common sense" would predict.

On top of that, soap tends to form colloids. A colloid is a variable mixture of droplets or particles of one material dispersed (spread) throughout another material. When you shake a vinaigrette salad dressing, the oil is dispersed as droplets throughout the vinegar and forms a temporary colloid. Soap likes to make colloids ... a lot ... and this alters how it behaves chemically.