AAMC FL Practice Exam

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Study for the AAMC FL Exam. Prepare with comprehensive flashcards and multiple-choice questions, each equipped with hints and explanations. Gear up for your medical school entrance exam!

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What formula is used to calculate pKa?

pKa = log [Ka]
pKa = Ka / 10
pKa = - log ka
pKa = Ka + 1

The correct answer is: pKa = - log ka

The correct formula to calculate pKa is derived from the relationship between the acid dissociation constant (Ka) and its negative logarithm. The formula expressed as pKa = -log(Ka) indicates that pKa represents the negative logarithm of the acid dissociation constant. This relationship is fundamentally important in acid-base chemistry because it provides a convenient way to express the strength of an acid: the lower the pKa, the stronger the acid. Understanding pKa is crucial because it reflects how easily an acid donates protons (H⁺ ions) in solution. A strong acid has a high Ka value and consequently a low pKa value. Conversely, a weak acid features a low Ka and a higher pKa. This logarithmic scale makes it easier to compare the relative strengths of various acids. In this context, the other choices do not accurately represent the calculation of pKa. For instance, the first choice incorrectly suggests a direct logarithmic relationship that is not aligned with the definition of pKa, while the second and fourth choices do not reflect standard practices in chemistry for converting between Ka and pKa. Understanding these relationships is vital for tackling problems involving acid-base equilibria and predicting the behavior of acids in different solutions.