Dental Admissions Test (DAT) Practice Test

What is the pKa value of a weak acid if its Ka is 1.0 x 10^-5?

1. 2

2. 5

3. 9

4. 10

The correct answer is: 10

The pKa value of a weak acid is equal to the negative logarithm of its Ka value. In this case, if the Ka value is 1.0 x 10^-5, then the pKa value would be -log (1.0 x 10^-5) = 5. Therefore, option D is the correct answer. The other options, A, B, and C, are incorrect because they either do not take into account the negative sign or they do not account for the given Ka value. Option A would be correct if the Ka value was 1.0 x 10^2, option B would be correct if the Ka value was 1.0 x 10^-1, and option C would be correct if the Ka value was 1.0 x 10^-9. However, since the Ka value given is 1.0 x 10^-5, none of these options are correct. Option D is the only one that correctly calculates the pKa value of a weak acid with a Ka value of 1.0 x 10^-5.