General Question

curiousjelly's avatar

Why is there fat in soap?

Asked by curiousjelly (21points) February 15th, 2010
19 responses
“Great Question” (5points)

What is it’s role, how does it help?

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MrGV's avatar

It improves the solidity and lathering qualities of soap; I think.

judochop's avatar

@gailcalled got modded? This shit is going over board.

drhat77's avatar

Soap is used to emulsify oil. Oil does not mix with water unless emulsified. So soap helps turn it into a form that, when you wash up, it can go down the drain instead of staying where it was.

What soap is is a large molecule which has a long tail which can dissolve in oil, and a salty head which can dissolve in water. This is what allows it to be emulsified – the soap helps turn the oil into a droplet which can float away.

The classic way to make soap was to take fat and stir it with a very caustic lye. This would destroy the oily head of the fat molecule, and leave a salty one in its place.

drhat77's avatar

@judochop -seriously, who knew?

drhat77's avatar

@judochop the ONLY reason I’d ever want to be a mod is to see all those posts that get deleted.

lilikoi's avatar

@drhat77 lol +1GA

Dog's avatar

[Mod Says:] Please folks. Please respect the asking party. This is a legit question It meets Fluther guidelines.

If you think the question is too basic move on to the next question and resist the temptation to post unhelpful remarks.


Dog (25137points)“Great Answer” (10points)
curiousjelly's avatar

Thank you @Dan_DeColumna and @MrGeneVan. Appreciate the answer.

Dan_DeColumna's avatar

I don’t think you mean to thank me.

gailcalled's avatar

Here is lots of information about fats and soap.


filmfann's avatar

From Fight Club:
Tyler Durden: Now, ancient people found their clothes got cleaner if they washed them at a certain spot in the river. You know why?
Narrator: No.
Tyler Durden: Human sacrifices were once made on the hills above this river. Bodies burnt, water speeded through the wood ashes to create lye.
[holds up a bottle]
Tyler Durden: This is lye – the crucial ingredient. The lye combined with the melted fat of the bodies, till a thick white soapy discharge crept into the river. May I see your hand, please?
[Tyler licks his lips until they’re gleaming wet – he takes the Narrator’s hand and kisses the back of it]
Narrator: What is this?
Tyler Durden: This…
[pours the lye on the Narrator’s hand]
Tyler Durden: ... is chemical burn.

SeventhSense's avatar

The first rule of Fight Club is we don’t talk about Fight Club.~

filmfann's avatar

@SeventhSense You sure? I thought that was the second rule.

SeventhSense's avatar

Doh! stop!

cazzie's avatar

Funny how this question got away from me. I MAKE soap. Soap is saponified oils (fats)...long chain fatty acids, what ever you want to call them.

To make soap from oils (fats..etc..) you make a strong alkali solution (high pH), usually with Sodium Hydroxide, otherwise known as lye. Everything is measured out very accurately and the chemistry tables are checked to make sure the balance is right so that there won’t be too much lye in the mix, ending up in a very harsh soap. In fact, most of us soap makers use a small percent extra of oil in our recipes to make sure the soap is mild and doesn’t strip the skin mantle.

So, when you take lye (NaOH) and add it to long chain fatty acids, it pulls those chains apart and create an entirely new substance. Soap, or soap salt. (chemically speaking, the resulting bar is made up of a soap salt, glycerine and usually some left over water and perhaps some perfume or essential oils and colourant like oxides of some sort.)

The soap salt will have a specific name, depending on the oil (fat etc) used in the mix. For example, I might use Olive oil, so saponified olive oil is called Sodium Olivate. Palm oil is called Sodium Palmate. I use veggie stuff in my soap, but you can see on the shelf at the grocery store stuff made with animal fat. It will have Sodium Tallowate (usually cow fat) listed and sometimes Sodium Lardate (pig fat).

MOST of the liquid soap you find is actually detergent, but some liquid soaps are real soaps and you can tell by reading the ingredient list. Liquid soap is made with Potassium Hydroxide instead of Sodium Hydroxide, so a saponified oil in a liquid soap might be called Potassium Cocoate (coconut fat or oil) it may just say,... the saponified oils of…. and then list the names of the oils used.

I hope this helps, and I realise this is half a year late.

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