I have a container with harmala acetate salt that has been dissolved in water. I start adding sodium carbonate. After a few grams, it turns milky and freebase harmala starts precipitating. Measure the ph: 10. So I add some more sodium carbonate, dissolve it, measure ph again: 10. Add more, measure: 10. Why is it that I can easily increase the ph of plain water to above 11, but when I do the same with water with harmala, it won’t go beyond 10? Thanks.

Sounds like chemical buffering to me…constant pH within a range, at some point one incremental molecule will dramatcally change pH…in this case, upward.

Thanks for the response. So I guess my question is: how high do I need to get the ph if I want to precipitate all the harmalas?

You might want to peruse this: https://wiki.dmt-nexus.me/Main_Page

Rule of 2.
pKa + 2 = >99% free base.

The above, plus this should answer your question: https://wiki.dmt-nexus.m..._and_Physical_Properties