At pH 7.4 which of the following bases exist mostly (more than 50%) in their protonated form? (pKaH values: methylamine 10.6, aniline 4.6, pyridine 5.2, imidazole 7.0, piperidine 11.1)

Amethylamine
Baniline
Cimidazole
Dpiperidine

Answer: A, D

A base is more than 50 percent protonated when pH < pKaH. Fractions protonated at pH 7.4: methylamine 0.9994, piperidine 0.9998, imidazole 0.28 (7.0 < 7.4), aniline 0.0016. So only methylamine and piperidine.

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At pH 7.4 which of the following bases exist mostly (more than 50%) in their protonated form? (pKaH values: methylamine 10.6, aniline 4.6, pyridine 5.2, imidazole 7.0, piperidine 11.1)

Answer: A, D

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