Question

What would be the equilibrium pH if 200 milligrams of Hydrofluoric acid (HF) were dissolved in 1 liter of

solution? The pK a for the acid is equal to 3.2. (Hint: Convert pKa to Ka)

HF <-- -> H + + F

Answer 1

Question #61566 – Chemistry – Organic Chemistry

2. What would be the equilibrium pH if 200 milligrams of Hydrofluoric acid (HF) were dissolved in 1 liter of solution? The pKa for the acid is equal to 3.2. (Hint: Convert pKa to Ka)

Solution:

$$HF \ll H + F$$ $$[H^+] = [F^-] + [OH^-]$$ $$C_{HF} = [HF] + [F^-]$$ $$K_a = [H^+][F^-]/[HF]$$ $$[H^+] = K_a C_{HF} / (H^+ + K_a) + K_W / [H^+]$$ $$C_{HF} = 0.2 / (20 \times 1) = 0.01 \text{ mol/l}$$ $$K_a = 10^{-3.2} = 6.3 \times 10^{-4}$$ $$[H^+] = 0.00222 \text{ mol/l}$$ $$pH = 2.65$$

Answer: $pH = 2.65$

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