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Okay, I'm a gen chem buff and usually destroy PS on practice tests. But like most others I have some acid/base/buffers anxiety but am still relatively good at them. This one passage-less problem on a past kaptest really bugs me as I can't seem to recall what I am missing here...
When 10mL of 1M K3PO4 solution is titrated with 1M HCl, the pH corresponding to the hydrophosphate/dihydrophosphate buffer region is found to be "X". What is the dissociation constant of dihydrophosphate?
A. 10^(1-X)
B. -log10^-X
C. 10^-X
D. 10^(1+X)
How I went about it...
pH = X = pKa + log(b/a)....pKa ---> -logKa
then raise everything onto 10 cause of the logs...
10^X = 10^(-logKa) + 10^log(b/a)
log rules from like 7th grade...(10^logA = A)
10^X = 1/Ka + (b/a)
easy parts over, now with the confusion...the answer is C. Ka = 10^-X
I see that somewhere, somehow "b/a" had to have been assumed 0..?
10^X = 1/Ka + 0 -----> Ka = 10^-X
wtf am I missing here
When 10mL of 1M K3PO4 solution is titrated with 1M HCl, the pH corresponding to the hydrophosphate/dihydrophosphate buffer region is found to be "X". What is the dissociation constant of dihydrophosphate?
A. 10^(1-X)
B. -log10^-X
C. 10^-X
D. 10^(1+X)
How I went about it...
pH = X = pKa + log(b/a)....pKa ---> -logKa
then raise everything onto 10 cause of the logs...
10^X = 10^(-logKa) + 10^log(b/a)
log rules from like 7th grade...(10^logA = A)
10^X = 1/Ka + (b/a)
easy parts over, now with the confusion...the answer is C. Ka = 10^-X
I see that somewhere, somehow "b/a" had to have been assumed 0..?
10^X = 1/Ka + 0 -----> Ka = 10^-X
wtf am I missing here

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