A buffer is prepared containing 0.300 molar boric acid and 0.500 molar dihydrogen borate. What is its pH? (pKa = 9. 27)
Question
A buffer is prepared containing 0.300 molar boric acid and 0.500 molar dihydrogen borate. What is its pH?
(pKa = 9. 27)
Solution
To solve this problem, we can use the Henderson-Hasselbalch equation, which is used to estimate the pH of a buffer solution. The equation is as follows:
pH = pKa + log([A-]/[HA])
where:
- pH is the pH of the buffer,
- pKa is the acid dissociation constant,
- [A-] is the concentration of the base (in this case, dihydrogen borate),
- [HA] is the concentration of the acid (in this case, boric acid).
Given in the problem, we have:
- pKa = 9.27,
- [A-] = 0.500 M (concentration of dihydrogen borate),
- [HA] = 0.300 M (concentration of boric acid).
Substituting these values into the Henderson-Hasselbalch equation, we get:
pH = 9.27 + log(0.500/0.300)
To simplify this, we first calculate the value of the log term:
log(0.500/0.300) = log(1.67) ≈ 0.22
Then we substitute this back into the equation:
pH = 9.27 + 0.22 = 9.49
So, the pH of the buffer solution is approximately 9.49.
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