Asked by Matt

I'm a tad confused by the question, The protonation constant for the acid HA has the value K=2*10^6.

(a) what is the principal species at pH 6.00?

(b) what is the principal species at pH 9.00?

(c) what is the quotient [A-]/[HA] at pH 6.3 and 7.5?
Answered by Devron
In solution:

HA <----> H^+ +A^-

Ka=[H^+][A^-]/[HA]

I've never heard the question asked this way either, but I think for A and B, the author of the question wants to know if A^-/H^+ or HA are the dominant species. The lower the pH, the more A^- you have; the higher the pH, the less A^- you have. This should be enough so that you can answer the first two by yourself.


For C:

Use the Henderson-Hasselbach equation

pH=pka-+log[A^-/HA]

pka=-log[Ka]

Solve for [A^-/HA] ratio:

10^(pH-pka)=[A^-/HA]



Answered by DrBob222
I must confess that I've never heard the term "protonation constant" used. Logic tells me this might be the reciprocal of Ka, the dissociation constant but I don't know that. Can you shed some light? If we can define what the protonation constant is I can help.
Answered by Anonymous
2) At 298K, what are the molarities of pure water?
Answered by DrBob222
Look up the density of water at 25C and use that to calculate the mass of 1000 mL. Ifound density at 25 C = 0.99705 g/mL; therefore 1000 mL has a mass of 997.05g.Then mols H2O = grams/molar mass = 997.05/18.015 = about 55.35 M
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