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.

Question

Deduce expressions for the fractions of each type of species present in an aqueous solution of lysine as a function of pH and plot the appropriate speciation diagram. Use the following values of the acidity constants: pKa (H3Lys2+) = 2.18. pKa (H2Lys+) = 8.95, pKa(Hlys) = 10.53.

Answer 1

Question

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.

Expert Solution & Answer

Trending nowThis is a popular solution!

See solution

Check out sample textbook solution

Students have asked these similar questions

Deduce expressions for the fractions of each type of species present in an aqueous solution of lysine as a function of pH and plot the appropriate speciation diagram. Use the following values of the acidity constants: pKa (H3Lys2+) = 2.18. pKa (H2Lys+) = 8.95, pKa(Hlys) = 10.53.

Calculate (to the nearest 0.1%) the proportion of a dose of ebastine (pKa of conjugate acid = 10.3) that will be ionised at pH 7.7. You do not need to include "%" in your answer.

The pKb of the organic base nicotine (denoted Nic) is 5.98. Write the corresponding protonation reaction, the deprotonation reaction of the conjugate acid, and the value of pKa for nicotine.