What is the Pka for potassium phosphate?

1 Answer
anor277
Jan 6, 2016

#pK_a# #=# #-log_(10)K_a#

Explanation:

#H_3PO_4 + H_2O rarr H_2PO_4^(-) + H_3O^+# #K_(a1) = 7.25xx10^(-3)#

#H_2PO_4^(-) + H_2O rarr HPO_4^(2-) + H_3O^+# #K_(a2) = 6.31xx10^(-8)#

#HPO_4^(2-) + H_2O rarr PO_4^(3-) + H_3O^+# #K_(a3) = 4.8xx10^(-13)#

I assume the one you want is for potassium dihydrogen phosphate, #K^+""^(-)OP(=O)(OH)_2#, i.e. #H_2PO_4^(2-)#.

#pK_(a2)# #=# #7.20#. See this link for a discussion of this acid-base behaviour.

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