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?
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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.