At the auto-ionization constant of water is

CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases

Problem

At 50 ∘C50\,^\circ\text{C} the auto-ionization constant of water is Kw=5.48×10−14K_w = 5.48 \times 10^{-14}. Hydrofluoric acid (HF) has an acid dissociation constant Ka=6.8×10−4K_a = 6.8 \times 10^{-4} at this temperature. A chemist studies fluoride-containing solutions under these conditions. (1) Part 1: Calculate the base dissociation constant, KbK_b, for the fluoride ion at 50 ∘C50\,^\circ\text{C}. (2) Part 2: Determine the pH of a 0.10 M0.10\,\text{M} aqueous solution of sodium fluoride (NaF) at 50 ∘C50\,^\circ\text{C}. Assume ideal solution behavior. (3) Part 3: A separate 0.10 M0.10\,\text{M} solution of HF is also prepared at 50 ∘C50\,^\circ\text{C}. Calculate the percent ionization of HF in this solution, and compare it with the percent ionization of the fluoride ion solution calculated in part (b). Explain the relationship between the two results.

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