Calculate the pH of a 0.21 M solution of NaA (K_a for HA is 2.1 × 10^-4) at 25°C. A) 11.82 B) 5.50 C) 8.50 D) 3.00 E) 2.18

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NaA is a salt of a weak acid (HA) and a strong base (NaOH). The solution will be basic. The pH can be calculated using the formula for the hydrolysis of the anion A⁻: pH = 14 - 0.5(pKa - log C), where pKa = -log(Ka) and C is the concentration of the salt. Here, pKa = -log(2.1 × 10⁻⁴) ≈ 3.68. Substituting the values, pH ≈ 14 - 0.5(3.68 - log(0.21)) ≈ 8.50.

Calculate the PH of a 0