What is the Pka for potassium phosphate?

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What is the Pka for potassium phosphate?

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Answer 1 · 2016-01-06T19:55:44

$p K_{a}$ $pK_a$ $=$ $=$ $- {log}_{10} K_{a}$ $-log_(10)K_a$

Explanation:

$H_{3} P O_{4} + H_{2} O \to H_{2} P O_{4}^{-} + H_{3} O^{+}$ $H_3PO_4 + H_2O rarr H_2PO_4^(-) + H_3O^+$ $K_{a 1} = 7.25 \times 10^{- 3}$ $K_(a1) = 7.25xx10^(-3)$

$H_{2} P O_{4}^{-} + H_{2} O \to H P O_{4}^{2 -} + H_{3} O^{+}$ $H_2PO_4^(-) + H_2O rarr HPO_4^(2-) + H_3O^+$ $K_{a 2} = 6.31 \times 10^{- 8}$ $K_(a2) = 6.31xx10^(-8)$

$H P O_{4}^{2 -} + H_{2} O \to P O_{4}^{3 -} + H_{3} O^{+}$ $HPO_4^(2-) + H_2O rarr PO_4^(3-) + H_3O^+$ $K_{a 3} = 4.8 \times 10^{- 13}$ $K_(a3) = 4.8xx10^(-13)$

I assume the one you want is for potassium dihydrogen phosphate, $K^{+}^{-} O P (= O) {(O H)}_{2}$ $K^+""^(-)OP(=O)(OH)_2$ , i.e. $H_{2} P O_{4}^{2 -}$ $H_2PO_4^(2-)$ .

$p K_{a 2}$ $pK_(a2)$ $=$ $=$ $7.20$ $7.20$ . See this link for a discussion of this acid-base behaviour.

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What is the Pka for potassium phosphate?

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