22. Consider a pH 8.00 solution of NaF, K-147 10 Calculate [F1 for this solution

Question

22. Consider a pH 8.00 solution of NaF, K-147 10 Calculate [F1 for this solution. a. b. What would be the solubility of Ca, K+" 3.9·w". this solution of NaF? c. What would be the pH of this solution if it was half-titrated by a strong acid? d. What would be the approximate pH of this solution i t was fully trated by an equal volume of acid? Assume that the approximation is valid (in reality it is not, but the pH obtained is very cdlose). 23. BONUS QUESTION. Determine Eoll and Go for the following reaction (10 points): Fe+ (aq) + Zn(s) Fe(s) + Zrte (a) E0.440 v Zn2-(aq) + 2e- Zn (s)

Explanation / Answer

a

F- + H2O <-> HF + OH-

Kb = [HF][OH-]/[F-]

1.47*10^-11 = x*x/(M-x)

x = [OH-] = 10^-pOH =10^-(14-pOH = 10^-6

1.47*10^-11 = (10^-6)(10^-6)/(M-10^-6)

M = (10^-6)(10^-6) / (1.47*10^-11) + 10^-6

M = 0.0680

b)

Ksp = [Ca+2][F-]^2

3.9*10^-11 = S * (0.0680^2)

S = (3.9*10^-11)/(0.0680^2)

S = 8.43*10^-9 M

c

pH for this solution when half titrated

F- + H+ = HF

pOH = pKb + log(HF/F-)

in half point, HF = F-

pOH = -log(1.47*10^-11) = 10.83

pH = 14-10.83

pH = 3.17

d

approximate pH in equivalence point

that is, when HF is present

Ka = X*x/(M-x)

10^-3.17 = x*x/(0.0680 - x)

x = 0.00645

pH = -log(0.00645) = 2.20 approx

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