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YellowGold

Naproxen is known to be a weak acid. In order to calculate its ka and pka, use the equation of getting the ph of weak acid which is ph= -1/2 log [(Ka)(Mwa)]. The Ka value is 3.18x10^-5. The pKa can be obtained through pKa = - log Ka. The pKa is 4.5. 

sebassandin

Answer:

[tex]Ka=6.43x10^{-5}[/tex]

[tex]pKa=4.19[/tex]

Explanation:

Hello,

In this case, the pH provides the concentration of hydrogen in its dissociation:

[tex]Naproxen\rightleftharpoons H^++Naproxen^-[/tex]

Thus, such concentration is:

[tex][H^+]=10^{-4.2}=6.31x10^{-5}M[/tex]

Thus, the Ka, by means of the dissociation law of mass action:

[tex]Ka=\frac{(6.31x10^{-5})^2}{1.25x10^{-4}-6.31x10^{-5}}=6.43x10^{-5}[/tex]

Hence the pKa is:

[tex]pKa=-log(Ka)=-log(6.43x10^{-5})=4.19[/tex]

Best regards.

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