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in Chemistry by (20 points)

A buffer solution contains 0.384 M KHCO3 and 0.239 M Na2CO3 . If 0.0464 moles of potassium hydroxide are added to 225.0 mL of this buffer, what is the PH of the resulting solution? (Assume the volume does not change upon adding potassium hydroxide.)

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1 Answer

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Calculate moles of bicarbonate and carbonate:
HCO3¯: (0.384 mol/L)(0.2250 L) = 0.0864 mol
CO32¯: (0.239 mol/L)(0.2250 L) = 0.053775 mol

The hydroxide reacts with the acid (the bicarbonate):
HCO3¯ decreases: 0.0864 - 0.0464 = 0.0400 mol
CO32¯ increases: 0.053775 + 0.0464 = 0.100175 mol

Need pKa of bicarbonate:
Ka of HCO3¯ is the same as the Ka2 of H2CO3.
Ka of HCO3¯ = 4.7 x 10¯11
pKa = 10.252

Use Henderson-Hasselbalch Equation:
pH = 10.328 + log (0.100 / 0.04)
pH = 10.328 + 0.398 = 10.726

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