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Author Topic: NaOH + NaCl  (Read 28895 times)

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nature boy

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NaOH + NaCl
« on: October 03, 2010, 11:09:52 PM »

Hello to everyone!
I'm making soap for quite some time. Lately i started to add table salt to the process to create harder soaps. I dissolved common table salt in distilled water and then add NaOH.
After continuous stirring the solution is cloudy with a texture like floating liquid particles (so i'm not 100% sure about the complete NaOH dissolving). The same result when add salt to the water  after NaOH dissolving (but the salt didn't dissolved well). The both finished products (soaps) has good desirable properties. I think is better to add the salt after NaOH so to be sure that NaOH has completely dissolved in the water. I don't like to add the salt at the end of saponification as others do, the soap took a texture with little white spots.
I want to know what actually happens when add common table salt (NaCl) to NaOH solution or vice-versa.
Thank you.
« Last Edit: October 08, 2010, 05:22:24 AM by Borek »
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nj_bartel

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Re: NaOH + NaCl
« Reply #1 on: October 04, 2010, 08:03:18 AM »

Nothing happens chemically, but the dissolved NaOH will reduce the amount of NaCl that can dissolve in solution (because NaOH is more soluble than NaCl, and there's a common ion effect with the sodium ion).  What may be happening is that you're causing the NaCl to crash out of solution when you add the NaOH.  You couldn't solve this problem by working in the reverse order though (adding NaCl to NaOH).

What you could do is use another highly soluble salt that doesn't have a common ion with NaOH, such as CaCl2.
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nature boy

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Re: NaOH + NaCl
« Reply #2 on: October 04, 2010, 12:02:24 PM »

Thank you very much for your reply nj_bartel !
Really helpful and interesting!
Be well.
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orgopete

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Re: NaOH + NaCl
« Reply #3 on: October 05, 2010, 05:05:34 AM »

Interesting question. I think nj answered it pretty well. However, I don't think CaCl2 would necessarily be a good addition. I am going to assume a good property of a soap is solubility. I am going to guess calcium salts are less soluble.

I am more interested in the rational for the addition in the first place. I think as nj_bartel pointed out, NaCl is going to have limited solubility. I further presume that a reasonably concentrated solution of NaOH is used to reduce the removal of water in making soap. So, is NaCl added to absorb water and speed setting of soap into bars or to add more water to the finished soap?
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nature boy

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Re: NaOH + NaCl
« Reply #4 on: October 05, 2010, 10:32:20 AM »

"So, is NaCl added to absorb water and speed setting of soap into bars"

That's true - but it's not the reason to add salt. In traditional soapmaking there is a procedure known as "salting out" (well known to chemists), used for the separation of the glycerin where the soap mass is treated with brine. But if you don't want to separate the glycerin, the adding of salt maybe reduces glycerin's properties and makes the soap harder and more stable.
Also I have read that CaCl2 reduces the lathering of soaps.
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orgopete

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Re: NaOH + NaCl
« Reply #5 on: October 05, 2010, 12:06:33 PM »

Thank you for the explanations. Some of us have too much book learning and not enough practical knowledge.

I presume calcium chloride or salt is the same as washing in hard water, less lather. If you put it into soap, you don't need to start with hard water to get the same effect. A new marketing angle, "You don't need a water softener, our soap can make soft water seem like hard". I suppose you will skip that.
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nj_bartel

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Re: NaOH + NaCl
« Reply #6 on: October 05, 2010, 01:27:25 PM »

Calcium chloride was very intentionally referred to as "such as" and not "use this"  :P
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nature boy

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Re: NaOH + NaCl
« Reply #7 on: November 24, 2010, 03:11:41 AM »

Hi to all.
I'm coming back to this thread to ask if the addition of NaCl is possible to weaken or strengthen the NaOH solution.
Thanks.
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cupid.callin

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Re: NaOH + NaCl
« Reply #8 on: November 24, 2010, 04:22:05 AM »

Mind me asking but "Which one is Stronger electrolyte? NaCl or NaOH?? "
Because the one which is weaker electrolyte will be effected by common ion effect ... no matter which one is added to solution first ... I GUESS!!!

And all salts (like NaCl) are strong electrolyte and every strong base(NaOH) is also strong electrolyte.
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AWK

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