Soap Making

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Annelisew
Posts: 2
Joined: Sun Aug 29, 2021 3:28 am
Occupation: Student

Soap Making

Post by Annelisew »

Hi Science Buddies,
I performed the experiment on soap making from ‘The Chemistry of Clean : Make Your Own Soap to Study Soap Synthesis’, but I’m having trouble with explaining the chemistry behind the purification.
I understand that after each round of salt purification the pH will decrease as NaOH is removed. But I’m struggling to explain why the pH initially increases after the first purification.
I did the experiment 5x and it always increased the first time.
I’d really appreciate any help given as to why the pH increases before decreasing. Thank you so much!! :D
ctactawong
Expert
Posts: 26
Joined: Thu Apr 30, 2020 7:56 am
Occupation: Other Adult

Re: Soap Making

Post by ctactawong »

Hello,

I think this is a very good question. It's important to understand why the observations did not match the theory. Could there be other chemicals in the oil and salt that you used? They may introduce additional reactions or act as buffer which could also change pH. I would suggest repeating the experiment with different brand of oil and salt.

It would be helpful if you can post your data.
Annelisew
Posts: 2
Joined: Sun Aug 29, 2021 3:28 am
Occupation: Student

Re: Soap Making

Post by Annelisew »

Thank you for your reply! I saw another forum on here about this exact experiment that said “the pH will be high after the first treatment, but it should decrease after the second or third time”, but they didn’t mention why.

Here are some of the results I got:
Trial 1
Crude Soap: pH8.5
Washed 1X: pH 9.8
Washed 2X: pH8.9
Washed 3X: pH 8.6
Washed 4X: pH 8.1
Washed 5X: pH7.8

Trial 4
Crude Soap: pH9.2
Washed 1X: pH 9.8
Washed 2X: pH9.5
Washed 3X: pH 9.2
Washed 4X: pH 8.6
Washed 5X: pH 8.5

My Calculation of the mean pH of the soap after each wash with NaCl
Crude Soap: pH9.26
Washed 1X: pH 9.90
Washed 2X: pH8.80
Washed 3X: pH 8.52
Washed 4X: pH 8.20
Washed 5X: pH7.96

Thank you so much! :)
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