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Today’s lesson: one idea in 3D, and the trap the MCAT sets around it.
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Your Red Pen Day: 25 minutes.
Day 1 is open. Days 2–90 come with the Pass.
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Today’s passage, timed, the way test day feels. Pick, then let the red pen correct you.
Open today’s passageMake it right
For each miss, write the one detail that would make your answer right. Then drill the trap that caught you.
One Trap Bank drillNever twice
The red pen review brings back yesterday’s misses, and the ones from 3 and 7 days ago, until you get each right three times in a row.
Open the red pen reviewTomorrow: a new lesson, a new passage, and the same 25 minutes.
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3,122 questions, so “today’s passage” never runs out.
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Try today’s idea on a course question.
From the coursefrom the course, Chem/Phys
Acetic acid (pKa 4.8) is more acidic than phenol (pKa 10), which is more acidic than ethanol (pKa 16). What best explains why phenol is more acidic than ethanol?
Pick one. The red pen does the rest.
The deciding lineAn acid is stronger when its conjugate base is more stable; delocalizing a negative charge by resonance stabilizes the base.
Why C: In phenoxide, the negative charge on oxygen is delocalized over the aromatic ring by resonance; ethoxide's charge stays on oxygen. The more stable conjugate base makes phenol the stronger acid.
Why each choice fails
- ARight effect, wrong mechanism: acidity here is explained by the stability of the conjugate base, not by hydrogen bonding of the acid.
- BSays more than the data: only the O–H hydrogen is acidic; the ring C–H bonds are not.
- CHolds: resonance-stabilized phenoxide.
- DLook-alike terms: both acids donate from an O–H bond with the same oxygen atom; atom size differs only between elements.
This is 1 of 3,122 questions in the Pass, all corrected like this one.
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