ACT Science Practice Question #1805 (Hard (580)) | Test Citadel
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ACT Science Difficulty: Hard (580)

Digital ACT Science Practice Question #1805

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At 30.0 mL of added NaOH, the solution acts as an effective chemical buffer because: Experiment Context (Dual Equivalence Points of Oxalic Acid): A 20.0 mL sample of 0.10 M oxalic acid (H2C2O4, diprotic) was titrated with 0.10 M NaOH. The reaction proceeds in two distinct deprotonation stages: Table 17: - 0.0 mL NaOH: pH = 1.30 - 10.0 mL NaOH: pH = 1.25 (Half-equivalence 1, pKa1) - 20.0 mL NaOH: pH = 2.85 (First Equivalence Point) - 30.0 mL NaOH: pH = 4.27 (Half-equivalence 2, pKa2) - 40.0 mL NaOH: pH = 8.40 (Second Equivalence Point) - 50.0 mL NaOH: pH = 12.10 (Excess Base)
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Buffer region: conjugate acid and base concentrations are equal.

Masterclass Solution & Distractor Trap Analysis

At the second half-equivalence point (30 mL), [HA-] = [A2-], creating maximum buffer capacity at pH = pKa2....

Distractor Analysis: Trap choice eliminates careless test-takers who confuse roots with coordinates...

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