Soaps are sodium or
potassium salts of fatty acids, prepared in a chemical reaction called
saponification. Originally soap was made by boiling lard or other animal fat
together with lye (sodium hydroxide) or potash (potassium hydroxide), as a
result of which crude soap and glycerol was formed. Nowadays animal fat is more
often replaced with all kinds of plant oils and butters such as olive oil,
coconut oil, castor oil, palm oil, cocoa butter, shea butter etc. Yet, still
sodium and potassium hydroxide are used in the process of soap making.
I am no expert on soap
making so I will leave writing great blog posts about soap making to those that
have years of experience with this craft. I am rather new to this topic and
have recently made my very first soap. This post is not about the properties of
soap making oils, or instructions on how to make soap. Actually you can find
all of this information on great websites such as:
What I do want to
write about in this post is something I was wondering about while making my
very first soap - does it make a difference whether I
use sodium hydroxide or potassium hydroxide to make my soap?
Anyone who took some
basic chemistry classes in high school probably remember that both sodium
hydroxide and potassium hydroxide are caustic bases formed from an alkali metal
ionically bound to a hydroxide group. Potassium is heavier then sodium, therefore
potassium hydroxide has a higher atomic weight then sodium hydroxide. Both
sodium and potassium hydroxide react with water generating heat (exothermic
reaction). The difference between these two hydroxides is that potassium
hydroxide reacts with water slightly less exothermic. Another difference is
that potassium hydroxide is more soluble in water then sodium hydroxide (121 g
of potassium hydroxide will dissolve in 100 ml of water compared to only 100 g
of sodium hydroxide in the same amount of water). Also potassium hydroxide is
cheaper then sodium hydroxide.
Getting back to my
question, does it matter if I use sodium or potassium hydroxide to make soap?
Will it give me the same results?
After a bit of research I learned that sodium
hydroxide is used to make bar or solid soap, whereas potassium hydroxide is
used to make liquid soap. Potassium hydroxide doesn't make a hard bar of soap
unless you use animal fat (lard, tallow etc). According to some people liquid
soap can also be made using sodium hydroxide (I've seen the recipes and the
outcome), but supposedly it doesn't make as nice of a soap as potassium
hydroxide. You can also mix sodium hydroxide with potassium hydroxide and make
what is called a hybrid soap. This gives a nice creamy soap. This difference
between soap made from potassium and sodium hydroxide can be somewhat explained
by the fact that sodium hydroxide soaps form crystals that clump together
giving harder soaps, whereas potassium soaps form strands leaving them more
liquid
Since we are already talking about soaps and sodium and potassium hydroxide I wanted to make it clear that real soap always has to be made from one of them! I often stumble across blog posts where people ask can you substitute the lye (sodium hydroxide) for something else in the soap. The answer is no. Yes, you can you sodium lauryl sulphate as for example the brand Lush does in some of its "soaps" (don't get me wrong I love most of their products). Its just that lets make it clear that something made form a detergent (like sodium lauryl sulphate) is not real soap anymore. Its just a detergent in a solid form.
And for those which are a bit afraid of a chemical like sodium hydroxide or potassium hydroxide let me assure you that if the soap is produced in a proper way all of the hydroxide is neutralised and in its place a salt is formed (to make sure the soap is completely neutralised pH papers are used).
Here a photo of glycerine melt and pour soap, which I have recently made
So excited that you're blogging again! This was a very informative post.
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DeleteCan u explain,does potassium hydroxide have any good benefits than sodium hydroxide to the human when using the liquid soap that contain KOH than NaOH ?
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