Calculate the ratio of NaF to HF required to create a buffer with pH = 3.90
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Calculate the ratio of NaF to HF required to create a buffer with pH = 3.90 Ka of HF is 6.8 × 10⁻⁴
Solution:
Whenever a problem says that there is a buffer, we can use Henderson-Hasselbach equation.
NaF is the base and HF is the conjugate acid (has one more hydrogen). Lets plug in the values and solve for the ratio.
3.90 = −log(6.8 × 10⁻⁴) + log([NaF]/[HF])
3.90 = 3.17 + log([NaF]/[HF])
0.73 = log([NaF]/[HF])
10^0.73 = [NaF]/[HF]
[NaF]/[HF] = 5.37
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