A hydrogen electrode placed in a buffer solution of CH3COONa and CH3COOH in the ratio's x:y and y:x has electrode potential values E1 and E2 volts, respectively, at 25°C. The pKa value of acetic acid

Question

A hydrogen electrode placed in a buffer solution of CH3COONa and CH3COOH in the ratio's x:y and y:x has electrode potential values E1 and E2 volts, respectively, at 25°C. The pKa value of acetic acid is

Prashant Kotian · Accepted Answer

Correct answer: C. E = -0.059 * pH. For ratio x:y, pH1 = pKa + log(x/y), so E1 = -0.059 * (pKa + log(x/y)). For ratio y:x, pH2 = pKa + log(y/x), so E2 = -0.059 * (pKa - log(x/y)). Adding these gives E1 + E2 = -0.059 * 2 * pKa = -0.118 * pKa. Thus, pKa = -(E1 + E2) / 0.118. Therefore, correct answer is C.

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