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Author: Subject: calculating required pH
Jhiggins94
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calculating required pH

hi, i have a query and im hoping someone on here could point me in the right direction.
how would one calculate the pH required to make a compound soluble in a given solvent?
say i was extracting a compound from a reaction mixture into a non polar, i wanted to form the freebase, how would i know how high to raise the pH?
any info would be greatly appreciated
horuse10
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You have to check the pKa of your compound of interest to calculate the right pH

Generaly use an excess of acid or base to drive of the compound out of your phase 1 to your phase 2, it doesn't really matter.

The only exception is if you compound can react with the excess of base or acid, in this situation you have to be careful of how much you add and monitor carefully the pH
Jhiggins94
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ok so if the compound had a pKa of 8.2 how would the pH correspond to that ?
so if in doubt just add acid/base dropwise untill it ceases to precipitate or all goes into solution (depending on disired result) then add a touch more?
horuse10
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pH=pKa+log([A-]/[AH])

With this formula you can calculate the proportion of acidic and basic forms with the pKa and a give pH

In practice your approch is right, just add a little more

 Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » calculating required pH Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues