Apentix/AP Chemistry/Unit 8: Acids and Bases/Question
AP Chemistryeasymcq1 pt

For carbonic acid, Ka1 = 4.3 × 10⁻⁷ and Ka2 = 5.6 × 10⁻¹¹. Why is Ka2 so much smaller?

A.The second proton sits on a more electronegative atom
B.Carbonic acid decomposes to CO₂ before the second step can occur
C.Successive Ka values always increase for polyprotic acids
D.Removing a positive proton from the already negative HCO₃⁻ ion costs electrostatic energy

Explanation

Core Concept

The first ionization strips H⁺ from a neutral H₂CO₃ molecule. The second must pull a positive proton away from an already negative HCO₃⁻ ion, and that attraction makes the loss far less favorable. Separating charge costs energy, so Ka2 sits orders of magnitude below Ka1.

Correct Answer

DRemoving a positive proton from the already negative HCO₃⁻ ion costs electrostatic energy

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