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Obsidian

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I need some chemistry advice deeanna, I don't know what I just created:)

I had been wanting to make a alum crystal deodorant soap like soaping101 does. Its a simple addition of alum crystals dissolved in the lye solution.

Well, I finally got around to trying it today but I dissolved the alum first then added the lye. When adding the lye, it volcanoed and got extremely hot but cooled very quickly

Everything dissolved but there was a lot of white sludge, similar to when you make brine soap. The smell is what had me worried though, it smelled like bad perm solution, ammonia and burned hair.

I was actually afraid to add the stuff to the oils, I didn't know what kind of chemical reaction I might get. Went ahead and mixed it all up, no other weird reactions and it traced just fine.

I have to wonder though, why did it volcano and did any of the lye get destroyed? Will my soap be ok? Was my mistake dissolving the alum first?
 

galaxyMLP

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I'm going to keep trying to answer these chemistry threads until I completely feel discouraged. However, I am not Dee Anna.

Alum is Aluminum Oxide, formula Al2O3.

Sodium Hdroxide is NaOH

When you combined Aluminum oxide and sodium hydroxide you are actually creating an acid base reaction.

In this case Al2O3 is the acid and NaOH is the base.

This reaction like most acid base reactions is exothermic and releases alot of heat (hence volcanoing).

The formula is:

Al203 + 2NaOH +3H2O --------------------> 2NaAl(OH)4

There are a few ways to write the formula to show the salts.

The product is called sodium aluminate (actually the way it is written is sodium aluminate (hydrated))

It is still a base (a little less strong than NaOH) but that is why you probably still got trace. You may notice that this soap has a higher superfat/less bubbles when it cures. Its also very likely that most of the NaOH was still present (especially if you only used a small amount of Alum) In this case you will actually have some alluminum salt soap and some sodium salt soap. :) Hopefully I'm helping this time.

Edit:

It is also possible that the "Alum" I referred to here is incorrect. The alum that I thought of is possibly wrong. Apparently traditional alum is KAl(SO4)2·12H2O.. It is a hydrated (contains water) sulfated potassium and aluminum species.

That makes a bit more sense now because sodium aluminate should be soluble in water however, you got s precipitate (the sludge).

I think the same general principle applies. I'm going to try to do a balanced equation and see what I come up with.
 
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Obsidian

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Thank you, makes perfect sense now. Guess I should have looked into this before hand, this particular recipe already had a high SF and I used a fair amount of alum.
 

galaxyMLP

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It should be interesting though. It might turn out nice. Although, I don't think aluminum salts of fatty acids are very soluble in water so you may get more soap scum than usual.

I am still trying to figure out what the "sludge" was.

I remember doing a chemistry lab with aluminum hydroxide and how it forms a gel in certain conditions. I cant remember if one of those conditions was a highly basic environment.

ETA: Just looked it up, apparently it dissolves in highly basic environments... Hmm....
 
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Obsidian

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Well, it turned into soap:) It does feel like it has higher SF but it lathers just fine and appears to be perfectly good soap. The initial large bubbles break down fairly quick to smaller bubbles but therr is a lot, most likely because I used more CO then normal. Will update in 6 weeks or so.
 

The Efficacious Gentleman

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Reading through this again, I do wonder if the aluminium in the alum would react like an aluminium pan would.........
 

Obsidian

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Galaxy, the alum I used is potassium aluminum sulfate. Its the stuff you buy as a deodorant crystal, the PH is generally around 3-4

Effy, I wondered about aluminum reaction too. I probably won't make this kind of soap again until I know if I was using the right kind of alum.
 

galaxyMLP

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Hmm, very interesting. Im a little at a loss for more explanation now...
 

Obsidian

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I still think your explanation is the most logical. The reaction when added to the lye is very similar to when you add citric acid to lye.
 

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