Interpretation:
The percentages of neutral and protonated forms present in a solution of 0.0010M pyrimidine at pH = 7.3 are to be calculated if the pKa of pyrimidinium ion is 1.3.
Concept introduction:
pH And pKa are related by Henderson-Hasselbalch equation as
Knowing pH and pKa values, the ratio between the two forms and from which their percentages can be determined.
To calculate:
The percentages of neutral and protonated forms present in a solution of 0.0010M pyrimidine at pH = 7.3, if the pKa of pyrimidinium ion is 1.3.
Answer:
At pH = 7.3, almost 100% pyrimidine molecules exist in the neutral form.
Explanation:
Deprotonation of the ammonium ion of a base can be represented as,
The Henderson-Hasselbalch can be written as
Substituting the values of pH and pKa, we get
Thus the concentration of neutral form is 106 times more than the protonated form. Hence almost 100% pyrimidine molecules exist in the neutral form.
Conclusion:
At pH = 7.3, almost 100% pyrimidine molecules exist in the neutral form.
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Chapter 24 Solutions
Organic Chemistry
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