Use the Henderson-Hasselbalch equation, eq. (3), to calculate the pH expected for a buffer solution prepared from this acid and its conjugate base, assuming: the mass of the weak acid is 0.2 g and the mass of the conjugate base is 0.2 g will be added to 25 mL of water. Also assume the molar mass of the weak acid is 234 and its conjugate base is the sodium salt.

Explanation:

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In this case, given the Henderson-Hasselbach equation, it is possible for us to compute the pH by firstly computing the concentration of the acid and the conjugate base; for this purpose we assume that the volume of the total solution is 0.025 L and the molar mass of the sodium base is 234 - 1 + 23 = 256 g/mol as one H is replaced by the Na:

And the concentrations are:

Then, considering that the Ka of this acid is 2.5x10⁻⁵, we obtain for the pH:

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