Which weak acid would be best to use when preparing a buffer solution with a pH of 8.50?
1) an acid with Ka=3.3x10^-9
2) an acid with Ka=5.0x10^-4
3) an acid with KA=6.3x10^-6
4) an acid with Ka=5.0x10^-7
5) an acid with Ka=4.0x10^-5
6) an acid with Ka=2.0x10^-10
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To determine the best weak acid to use when preparing a buffer solution with a pH of 8.50, we need to choose an acid with a pKa close to 8.50. The pKa is the negative logarithm of the acid dissociation constant (Ka).
To calculate the pKa from Ka, we use the formula: pKa = -log(Ka).
Let's calculate the pKa for each option:
Option 1: pKa = -log(3.3x10^-9)
Option 2: pKa = -log(5.0x10^-4)
Option 3: pKa = -log(6.3x10^-6)
Option 4: pKa = -log(5.0x10^-7)
Option 5: pKa = -log(4.0x10^-5)
Option 6: pKa = -log(2.0x10^-10)
Now, we compare the calculated pKa values with the desired pH of 8.50. The pKa value closest to 8.50 would be the ideal weak acid to use.
Comparing the pKa values:
Option 1: pKa ≈ 8.48
Option 2: pKa ≈ 3.3
Option 3: pKa ≈ 5.2
Option 4: pKa ≈ 6.3
Option 5: pKa ≈ 4.4
Option 6: pKa ≈ 9.70
Based on the calculated pKa values, the weak acid with an acid dissociation constant (Ka) of 3.3x10^-9 (Option 1) would be the best choice for preparing a buffer solution with a pH of 8.50.