neutralisation (saponification) of stearic acid - calculation

Formulating

neutralisation (saponification) of stearic acid - calculation

Posted by magdziurek on February 11, 2016 at 6:37 pm

Hi !

My goal is to create lotion with NaoH /stearic acid as emulsifier.

My oil phase is:

15% mineral oil

20% isopropyl myristate

I need to calculate how much NaOH is needed to saponify 5% stearic acid.

Chemical reaction will be as follow:

C₁₇H₃₅COOH + NaOH ⇒ C₁₇H₃₅COONa + H₂O

My question is should I included saponification value for stearic acid or treat this calculation as normal proportion:

284.4772 g/mol - 40 g/mol

5% - x

Second option as I have mentioned is taking into account saponification value for stearic acid which is between 206 and 212, so let’s say for calculation purpose we will take 209.

So then I would have to recount amount KOH for the NaOH.

It seems to be easy, but I think I am lost here !

Any help ?

Dilfre replied 8 years, 8 months ago 4 Members · 8 Replies
8 Replies

Bobzchemist

Member
February 11, 2016 at 7:11 pm

1) If this confuses you, why not just use pre-made sodium stearate? Working with NaOH isn’t all that safe, and you don’t safe money making it from scratch until you start making batches larger than 500 kilos.

2) Sodium Stearate is a lousy emulsifier. You will need at least one, but preferably two or more co-emulsifiers to make a stable formula. Why not just use one of the polymeric emulsifiers and save yourself massive levels of aggravation?

3) Honestly, now that I think about it, if this sort of calculation confuses you, it is not safe for you to be formulating at all, even if you only use your lotions on yourself. I very strongly recommend that you stick with pre-made, pre-tested lotion bases, or better yet, learn much more about chemistry and lab safety before doing any of this sort of work.
belassi

Member
February 11, 2016 at 7:15 pm

Doesn’t sound like anything I would want to put on myself, but if you really want to do that calculation, simply use http://soapcalc.net/calc/SoapCalcWP.asp
magdziurek

Member
February 11, 2016 at 10:10 pm

Belassi - Many thanks, however this calculator does not apply to my case I have pure stearic acid and I am not using any oil containing tryglycerides.

Bobzchemist - My goal is learning indeed, I understand that you have lot of experience but I start to formulate and would like to understand from basic and not using pre made stuff. I will make another batch with addition of anionic emulsifier to obtain more stable emulsion.

Regarding to calculation - I think this is simple calculation as below, but if someone could confirm or correct me would be great !

284.4772 g/mol - 40 g/mol

5g - x

x=0.703 g pure NaOH
belassi

Member
February 11, 2016 at 10:13 pm

If you bother to actually check the calculator I gave you, you will find stearic acid listed there.
magdziurek

Member
February 11, 2016 at 10:42 pm

Hi,

Of course I meant addition of nonionic emulsifier.

Belassi - I have seen this calculator but I need to choose oils - mineral and isopropyl myristate and I could not find it on the list of oils there..
belassi

Member
February 11, 2016 at 11:36 pm

For good reason. Mineral oil, for instance, cannot be saponified. The isopropyl myristate should not be saponified but added after saponification is complete. I am beginning to think that you don’t have the knowledge at this moment, to go ahead with this project. I recommend bringing someone into your plans who understands these things.
magdziurek

Member
February 12, 2016 at 8:28 am

Yes I know that I want to saponify my stearic acid not oils as they do not have any tryglicerides. Anyway thanks for all responses.
Dilfre

Member
July 9, 2016 at 1:56 am

At mendrulandia page there is a very good saponicalculator, is in spanish and is easy to use. Regards

http://calc.mendrulandia.es/