A buffer solution is made using a weak acid, HA. If the pH of the buffer is 1.0 × 101 and the ratio of A– to HA is 10, what is the pKa of HA?

http://www.jiskha.com/display.cgi?id=1374195842

To find the pKa of HA, we need to use the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the pKa of the weak acid and the ratio of its conjugate base to the weak acid.

The Henderson-Hasselbalch equation is given by:

pH = pKa + log([A-]/[HA])

In this case, we are given the pH, which is 1.0 × 10^1, and the ratio of [A-] to [HA], which is 10. Let's substitute these values into the equation:

1.0 × 10^1 = pKa + log(10)

Since log(10) = 1, the equation simplifies to:

1.0 × 10^1 = pKa + 1

Now, let's isolate pKa by subtracting 1 from both sides:

pKa = 1.0 × 10^1 - 1

pKa = 10 - 1

pKa = 9

Therefore, the pKa of HA is 9.