0
$\begingroup$

is phenolate a strong or weak base? I have read somewhere that it would be a weak base. However, since phenolate is the conjugate base of phenol, which is a weak acid, I would think that phenolate is a strong base. My general understanding is that strong conjugate base or acid is formed from a weak acid or base, respectively. Could someone help me?

$\endgroup$
5
  • 2
    $\begingroup$ "I have read somewhere that it would be a weak base." Please tell us where. Without that knowledge we can not know the context within which the comment was made, and this can not answer your question fully. Yes, phenolate would normal be consider a reasonably strong base due to the reason you give. But the original might have been a comparison with sodium hydride, or in a strange solvent, or something else - we need to know. $\endgroup$
    – Ian Bush
    Oct 7, 2023 at 12:45
  • 2
    $\begingroup$ Evaluate it quantitatively. Take the phenol acidity constant and compute the phenolate basicity constant. Then make conclusion. $\endgroup$
    – Poutnik
    Oct 7, 2023 at 13:03
  • 1
    $\begingroup$ There are levels upon levels upon levels of different meanings for "strong" and "weak", and on top of that there are more levels. Are you big or small? A Stentor can grow to 2mm, which makes it a giant among ciliates. On the other hand, an adult Indian elephant is pretty small compared to Taj Mahal. Same thing here. $\endgroup$ Oct 7, 2023 at 13:17
  • 1
    $\begingroup$ The old name for phenol is carbolic acid, does that sound like a weak acid? $\endgroup$
    – Waylander
    Oct 7, 2023 at 17:50
  • $\begingroup$ Phenol is a stronger acid than water meaning its conjugate base is weaker than OH- but stronger than bases such as acetate, bicarbonate or ammonia? that have stronger conjugate acids. [ Do the math to be sure.] Your reasoning is fine but you forget that water is an acid too and acid strengths are relative to its strength. $\endgroup$
    – jimchmst
    Oct 7, 2023 at 19:28

1 Answer 1

2
$\begingroup$

Whether a base is considered strong or weak depends heavily on context. It is thus much better to consider the relative strength of acids and of bases rather than making absolute statements that one acid is strong or weak. This is best done by comparing the pKa values of acids (or conjugate acids in the case of bases). Phenol has a pKa of about 10.0 so it is a stronger acid than water (pKa 15.7), but weaker than acetic acid (pKa 4.8). You are correct that when comparing two acids, the stronger acid has the weaker conjugate base and vice versa. Therefore, we would expect phenolate (conjugate base of phenol) to be a stronger base than the acetate (conjugate base of acetic acid), but a weaker base than hydroxide (the conjugate base of water).

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.