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 10 6 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 24.5, Problem 7P

Interpretation Introduction

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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