1. During the titration of an unknown weak acid with NaOH, it was determined tha
ID: 985240 • Letter: 1
Question
1.
During the titration of an unknown weak acid with NaOH, it was determined that the pH=4.36 after 16.24 mL of 0.0984 F NaOH was added. This pH and volume was measured before the equivalence point occurred.
Calculate the moles of conjugate base (A-) produced from the addition of base.
2.
During the titration of an unknown weak acid with NaOH, it was determined that the pH=4.36 after 16.24 mL of 0.0984 F NaOH was added. This pH and volume was measured before the equivalence point occurred.
In the previous question you calculated the moles of conjugate base.
Now, calculate the moles of weak acid (HA) that remains in solution if 0.5123 g of weak acid was used in the titration. Assume that the molecular weight of the acid is 100.18 g.
3.
During the titration of an unknown weak acid with NaOH, it was determined that the pH=4.36 after 16.24 mL of 0.0984 F NaOH was added. This pH and volume was measured before the equivalence point occurred.
In the previous questions you calculated the moles of conjugate base and the moles of weak acid that remain.
Now, calculate the pKa of the weak acid.
Explanation / Answer
1. No of moles of NaOH added = 0.0984*(16.24/1000) = 0.0016 mol
No of moles of NaOH added = No of moles of conjugate base(A-) = 0.0016 mol
2.
No of mole of weak acid used = 0.5123/100.18 = 0.0051 mol
No of mole of weak acid remains = 0.0051 - 0.0016 = 0.0035 mol
3. pH = pka + log(conjugate base / acid)
4.36 = x + log(0.0016/0.0035)
x = pka of buffer = 4.7
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