Figuring out a chemical mistake

[ronthepon]

There was recently a little accident in a school lab nearby, and I'm interested in hearing the opinions of you science guys on it.

It was chemistry practical time, and the kids were making some soap by saponification.

First they brought some fat

Then, they added NaOH, rather in excess.

They heated the mixture for about 10 mins

They then put the remainder in casts to make soap and left in the sun to dry.

About 2 hours later, the lab assistant found that the mixture was too basic and was causing severe ichiness in anybody who would bother to touch it.
So he added some concentrated acid, slowly.

About 45 mins. later, the soaps violently exploded, causing the laboratory to become a complete mess.

Anybody got any idea waht happened? The lab assistant says that he added the acid quite slowly and carefully, and anyway I think that 45 minutes is a very long reaction time.

[Mercedes Benzene]

That is utterly perplexing!

I couldn't really begin to imagine how something like that would happen. Perhaps there was some sort of impurity in the fat??? Or perhaps some error in the experiment formed some combustible organic compounds in the recently created soap.
Another point to make: You mentioned that the soap caused itchiness. Bases don't itch. The skin may feel irritated, but it definitely doesn't itch. This suggests that maybe there was some additional contaminant??
This is really strange.... but very cool.

[ronthepon]

The fat happened to be pure enough to be worth human consumption. And anyway, as far as I can guess, the experiment has been done before in the school.

[Mercedes Benzene]

Weird.

[Jay-qu]

I dont get it.. do you mean to say acid was added and then 45mins of nothing then bang? acid base reactions are exothermic (release heat) maybe the fat combusted after to much heat built up within the mixture

[ronthepon]

Actually I'll take a guess that the acid was not the reason that the mixture blew up.

By the way, I think it was sulphuric or nitric acid he added...

[Jay-qu]

both strong acids reacting with a strong base.. so what would you suppose did it then?

[ronthepon]

But 45 minutes is a positive. The lab. assistant also claims that he did it slowly...

[UncleAl]

1) When making soap for human use, one would do well to follow a proven recipe. Lye soap with excess lye is nobody's idea of a good time.

http://www.turoks.net/Cabana/ItsInTheBook.htm
exception noted.

2) Did they press out the glycerin?

3) Did the git acidify glycerin-containing soap with nitric acid, as in nitroglycerin?

[ronthepon]

Originally Posted by UncleAl

2) Did they press out the glycerin?

3) Did the git acidify glycerin-containing soap with nitric acid, as in nitroglycerin?

n... nitroglycerin?!

Well can it be made so easily?

I'll check up with the batch of students!