Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: ginger on 06/04/2004 07:34:45
-
In simple terms could someone please answer the following question.
If sodium carbonate + water is used as a base to sap a fatty acid, will it produce glycerine as a byproduct of the reaction the same way sodium hydroxide or potassium hydroxide will
Thanks
Ginger
-
Saponification is the hydrolysis of the ester linkages between fatty acids and glycerol. The process requires the presence of a strong base (hence, as you correctly assert, KOH (potassium hydroxide) or NaOH (sodium hydroxide) :
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fchemistry.about.com%2Flibrary%2Fgraphics%2Fsoap.gif&hash=7149f7b019c2a2708b83b6eb691a4584)
To my knowledge there is no reason why sodium carbonate will not work, although it might be possible to heat the hell out of it to drive off the CO2. The result will be NaO which you can dampen to produce NaOH.
chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
Hi Chris
Thanks for that. Much appreciated:-)) I know that Marseilles Soap is made with sodium carbonate and they boil it in big kettles (cauldrons) but as they sell it in it's basic form as a laundry soap, I was unsure as to whether glycerin was a product of the reaction. Thanks again
Ginger
Life is not measured by the number of breaths we take, but by the moments
that take our breath away
-
What is happening chemically when I make soap? I dissolve lye crystals in water and when that cools, fat (grease from bacon, sausages...) is added.
-
The reaction is as shown above. Lye (the sodium hydroxide - NaOH) breaks the ester linkage bonding the fatty acid and the glycerol together.
The base 'adds water' (H2O) or hydrolyses the ester link -O- to regenerate the fatty acid and the alcohol (glycerol). The fatty acid reacts with the base (sodium hydroxide) to produce the sodium salt of the fatty acid.
So if the fat were animal fat, in other words a triglyceride like your bacon fat which comprises 3 palmitic (fatty) acids (containing chains of 16 carbon atoms) stuck to glycerol, when you add the sodium hydroxide you get sodium palmitate (the sodium salt) and glycerol.
The soap works by using the charged polar end of the molecule (the COO - part) to stick to water, and the non-polar organic fatty tail to stick to oils. This way it can bring oil and water together and enable water to mix with fat.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
Thanks Chris, that's really interesting; I've been wondering about it for a while. Any idea how I could make soap that lathers when used?
After I make the soap, it sits for a day or two until it's hard enough to cut into bars, then it's cured in the open air for about six weeks. When it's becoming solid, is it just because the polar ends are still connecting, or is the water evaporating? Why does it need to cure for so long? If I use it before it's ready, it burns. And what is the effect when I add things like flower petals, spice, oatmeal, pumpkin, lemon rind, and that sort of thing?
-
Saponification is the hydrolysis of the ester linkages between fatty acids and glycerol. The process requires the presence of a strong base (hence, as you correctly assert, KOH (potassium hydroxide) or NaOH (sodium hydroxide) :
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fchemistry.about.com%2Flibrary%2Fgraphics%2Fsoap.gif&hash=7149f7b019c2a2708b83b6eb691a4584)
To my knowledge there is no reason why sodium carbonate will not work, although it might be possible to heat the hell out of it to drive off the CO2. The result will be NaO which you can dampen to produce NaOH.
chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
Hi Chris
Thanks for that. Much appreciated:-)) I know that Marseilles Soap is made with sodium carbonate and they boil it in big kettles (cauldrons) but as they sell it in it's basic form as a laundry soap, I was unsure as to whether glycerin was a product of the reaction. Thanks again
Ginger
Life is not measured by the number of breaths we take, but by the moments
that take our breath away
-
What is happening chemically when I make soap? I dissolve lye crystals in water and when that cools, fat (grease from bacon, sausages...) is added.
-
The reaction is as shown above. Lye (the sodium hydroxide - NaOH) breaks the ester linkage bonding the fatty acid and the glycerol together.
The base 'adds water' (H2O) or hydrolyses the ester link -O- to regenerate the fatty acid and the alcohol (glycerol). The fatty acid reacts with the base (sodium hydroxide) to produce the sodium salt of the fatty acid.
So if the fat were animal fat, in other words a triglyceride like your bacon fat which comprises 3 palmitic (fatty) acids (containing chains of 16 carbon atoms) stuck to glycerol, when you add the sodium hydroxide you get sodium palmitate (the sodium salt) and glycerol.
The soap works by using the charged polar end of the molecule (the COO - part) to stick to water, and the non-polar organic fatty tail to stick to oils. This way it can bring oil and water together and enable water to mix with fat.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
Thanks Chris, that's really interesting; I've been wondering about it for a while. Any idea how I could make soap that lathers when used?
After I make the soap, it sits for a day or two until it's hard enough to cut into bars, then it's cured in the open air for about six weeks. When it's becoming solid, is it just because the polar ends are still connecting, or is the water evaporating? Why does it need to cure for so long? If I use it before it's ready, it burns. And what is the effect when I add things like flower petals, spice, oatmeal, pumpkin, lemon rind, and that sort of thing?