The following graph presents the titration curve of oxalic acid with sodium hydr

Question

The following graph presents the titration curve of oxalic acid with sodium hydroxide. (a) Explain what is the equivalent point and identity the volume of NaOH used at the equivalent point in the above the graph. Explain and show how do you determine the pK_a for oxalic acid from the above titration graph In "Disturbing Chemical Reaction at Equilibrium", we studied the following reversible exothermic reaction Fe^3+ (aq) + SCN^- (aq) leftrightarrow Fc(SCN)^2- (aq) + energy colorless colorless Amber (a) To a test tube that contained the mixtures of the reagents at equilibrium, you added additional 3-4 drops of 0.1M Fe^3+ solution, what color change do you expect to see? Indicate which direction (left or right) the equilibrium is shifted to (b) Again to this test tube you add additional 0.1M SCN^- solution to the mixture, what color change do you expect to see? Indicate which direction (left or right) the equilibrium is shifted to

Explanation / Answer

Q4.

a)

equivalence point --> th epoint in which [H+] = [OH-]

in this graph, it is when pH changes drastically, so about V = 30 mL

b)

for pKa, we need the half equivlaence point

since

pH = pK a+ log(A-/HA)

in the half point A- = HA so log(1) = 0

therefore

pH = pKa

at V = 30/2 = 15 mL

choose

pKa = 2 approx (the pH at V = 15 mL)

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