# is pKa the same as pH?

Discussion in 'DAT Discussions' started by drzakisadiq, 07.28.08.

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1. ### drzakisadiq 2+ Year Member

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just wondering, a bit confused on terminology here.

3. ### Albuterol 7+ Year Member

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pKa = -log of [Ka]
pH = -log of [H+]

Ka is the acid dissociation constant = [H+][A-]/[HA]

pH= pKa when the conjugate base = weak acid at the half-way point on a titration curve

the lower the pKa the more acidic the solution is
the lower the pH the more acidic the solution is

4. ### drzakisadiq 2+ Year Member

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thanks, so if in a problem i were given the pKa, how would i convert that to pH?

5. ### PreDent2009 5+ Year Member

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They would also have to give you the concentration of the acid and its conjugate base so you could use the henderson hasselbach formula. Otherwise, it would be pretty impossible to derive the pKa. You can however tell whether the acid is strong or weak, etc.

6. ### Albuterol 7+ Year Member

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u can use the henderson-hasselbach equation
pH= pKa + log [conj base]/[wa]

im not sure of others but hopefully someone else knows.

7. ### doc3232 7+ Year Member

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You can compare the two, but they are not the same.
They are equal only if [HA] = [A-]