is there difference between pka and pH?

[Smooth Operater]

is there difference between pka and pH? I wonder what is the difference? does pH always equal to pKa? Thanks!

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[jhuplaw]

pka is the acid dissociation constant and ph is a measure of acidity. the only relationship between the two that i can remember is the henderson-hasselbalch equation:

ph = pka + log(A-/HA)

 

[haavoc]

pH = pKa when concentrations of the conjugate base and its conjugate acid are equal, i.e., pH = pKa + log(1) --> pH = pKa b/c log(1) = 0