Chemistry

Problem

A 25.00 mL sample of a diprotic acid H₂A of unknown concentration is titrated with 0.100 M NaOH at 25 °C. The first sudden rise in pH occurs at a burette reading of 18.20 mL; the second occurs at 36.40 mL. The pH is carefully recorded at two additional key volumes: • 9.10 mL of NaOH added: pH = 2.90 • 27.30 mL of NaOH added: pH = 7.60 (a) Determine the molarity of the original H₂A solution. (b) Calculate

pK_{a1}

and

K_{a1}

for the first ionization step. (c) Calculate

pK_{a2}

and

K_{a2}

for the second ionization step. (d) Rank the strengths of H₂A, HA⁻, and A²⁻ as Brønsted acids. Justify the ranking using numerical evidence. (e) Sketch (no numerical scale required) the qualitative shape of the complete titration curve for this experiment, clearly indicating the buffer regions and both equivalence points. Annotate your sketch with the pH values calculated in parts (b) and (c). (a) Find the concentration of the original H₂A solution. (b) Determine

pK_{a1}

and

K_{a1}

. (c) Determine

pK_{a2}

and

K_{a2}

. (d) Rank H₂A, HA⁻, and A²⁻ in acid strength with justification. (e) Produce and annotate a qualitative sketch of the titration curve.

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