Question

1) Rank the following titrations in order of increasing pH at the halfway point to equivalence (1 = lowest pH and 5 = highest pH).

100.0 mL of 0.100 M KOH by 0.100 M HCl

100.0 mL of 0.100 M HC₃H₅O₂ (K_a = 1.3 x 10^-5) by 0.100 M NaOH

100.0 mL of 0.100 M C₂H₅NH₂ (K_b = 5.6 x 10^-4) by 0.100 M HCl

100.0 mL of 0.100 M HF (K_a = 7.2 x 10^-4) by 0.100 M NaOH

200.0 mL of 0.100 M H₂NNH₂ (K_b = 3.0 x 10^-6) by 0.100 M HCl

Answer 1

Position 1: Titration of H2NNH2 and HCl, is the weakest base (smallest Kb) with a strong acid.

Position 2: Titration of C2H5NH2 and HCl, is the weakest base (highest Kb) with strong acid.

Position 3: Titration of KOH and HCl, acid and strong base, the pH is equal to 7.

Position 4: Titration of HF and NaOH, is the weakest acid (greater Ka) with a strong base.

Position 5: Titration of HC3H5O2 and NaOH, weaker acid (lower Ka) and strong base.

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