If Ka = 1.0 × 10^-5, what is pKa?

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Multiple Choice

If Ka = 1.0 × 10^-5, what is pKa?

Explanation:
pKa is the negative base-10 logarithm of Ka, so pKa = -log10(Ka). With Ka = 1.0 × 10^-5, log10(Ka) = log10(1.0) + log10(10^-5) = 0 - 5 = -5. Therefore, pKa = -(-5) = 5. This value means Ka corresponds to 1.0 × 10^-5, since a pKa of 5 is the negative log of 10^-5. The other numbers would imply different Ka values (for example, a pKa of -5 would require Ka = 10^5, a pKa of 9 would require Ka = 10^-9, and a pKa of 14 would require Ka = 10^-14).

pKa is the negative base-10 logarithm of Ka, so pKa = -log10(Ka). With Ka = 1.0 × 10^-5, log10(Ka) = log10(1.0) + log10(10^-5) = 0 - 5 = -5. Therefore, pKa = -(-5) = 5.

This value means Ka corresponds to 1.0 × 10^-5, since a pKa of 5 is the negative log of 10^-5. The other numbers would imply different Ka values (for example, a pKa of -5 would require Ka = 10^5, a pKa of 9 would require Ka = 10^-9, and a pKa of 14 would require Ka = 10^-14).

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