Buffers, chemical reactions, and the like

(I have a very, very shallow understanding of the topic, so please bear with me!)

So I've been reading up on buffers. From my understanding, they involve weak acids/bases paired with their corresponding salt (e.g. citric acid/sodium citrate). I also learned that acid + base = water + salt. 

In beauty circles, people use bentonite clay with ACV to bring the clay's pH down. I came up with the idea to add lactic acid instead, both to lower the clay's pH and to give the mask some exfoliating function. So I prepared a montmorillonite mask and added 10% lactic acid to it, which caused the stuff to bubble profusely. I tested the pH, which came around to ~5.5. I then added citric acid to bring the pH down to ~3.8. My skin is accustomed to acids, so the mask didn't feel any different from other clay masks.

The clay in question is CosBlue.

My questions are:

1. Was the lactic acid rendered useless by the chemical reaction?
2. If neutralized, did the lactic acid turn to sodium lactate?
3. Basic bonus question: Is 'buffer' = 'pH adjuster' in terms of cosmetic formulation?


  • PerryPerry Administrator, Professional Chemist
    Could you list all the ingredients in your formula?  Without that information it's difficult to answer. For example, you don't mention water. Without water how are you taking pH?

    But in general, a weak acid compound like lactic acid is going to exist in a solution of water as both the acid and its conjugate base (lactate). The lower the pH, the more the equilibrium equation shifts away from the lactate to the acid.

    Image result for lactic acid equilibrium equation 

    Here is a good basic review of acid and base chemistry.
  • Hi Perry, thanks for taking the time to answer. 

    The formula is 60% clay, 10% lactic acid, and 30% distilled water.

    Thanks for the link as well, it's going to be a very helpful. 
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