For a drug that is a weak base with a pKa of 8.4, the predominant species at pH 7.4 will be: 

Question

For a drug that is a weak base with a pKa of 8.4, the predominant species at pH 7.4 will be:

BlackTom AI · Accepted Answer

First, let's identify what the question is asking: at pH 7.4, for a drug that is a weak base with a pKa of its conjugate acid (8.4), which form is predominant?
Option 1: Positively charged. This is the correct choice. For a weak base, the protonated form (BH+) is positively charged. Since pH 7.4 is one unit below the conjugate acid pKa of 8.4, Henderson–Hasselbalch for bases tells us the ratio of unprotonated base (B) to protonated form (BH+) is [B]/[BH+] = 10^(pH - pKa) = 10^(7.4 - 8.4) = 10^(-1) = 0.1. That means most molecules are in the BH+ form, i.e., positively charged.
Option 2: Uncharged. This would require a larger fraction of B relative to BH+. The calculated ratio (0.1) means only about one part B for ten parts BH+, so the uncharged form is not predominant at pH 7.4.
Option 3: Negatively charged. Protonation of a base yields BH+. Deprotonation to form a negatively charged species would require the molecule to lose a proton below neutral pH, which is not supported by the base’s behavior here. The equilibrium at pH 7.4 does not favor a negative charge for a weak base with pKa 8.4.
Option 4: Zwitterionic. A zwitterion would require simultaneous positive and negative charges on different sites in the same molecule. The Henderson–Hasselbalch data here do not indicate formation of a structure carrying both charges; the dominant form is simply BH+ (positively charged) with the neutral base being minority.
In summary, because the solution pH is lower than the base’s conjugate acid pKa, the equilibrium favors protonation to BH+, yielding a positively charged predominant species. The other options misinterpret protonation balance, charge state, or the possibility of internal charge separation.

For a drug that is a weak base with a pKa of 8.4, the predominant species at pH 7.4 will be:  Single choice

Similar Questions

Salbutamol (structure below, pKa 9.3):

Salbutamol (structure below, pKa 9.3):

Which of the following regarding the influence of pH on drug passage through membranes is INCORRECT?

Salbutamol (structure below, pKa 9.3):

Aspirin is a weak acid drug (pKa 3.5) and propranolol is a weak base (pKa 9.5). Which ONE of the following statements regarding their in vivo disposition is correct?

According to Xenophanes, what should be avoided at a symposium?

What is "kottabos"?

Why are there so many naked figures in vase iconography?

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler

For a drug that is a weak base with a pKa of 8.4, the predominant species at pH 7.4 will be: Single choice

Similar Questions

Salbutamol (structure below, pKa 9.3):

Salbutamol (structure below, pKa 9.3):

Which of the following regarding the influence of pH on drug passage through membranes is INCORRECT?

Salbutamol (structure below, pKa 9.3):

Aspirin is a weak acid drug (pKa 3.5) and propranolol is a weak base (pKa 9.5). Which ONE of the following statements regarding their in vivo disposition is correct?

According to Xenophanes, what should be avoided at a symposium?

What is "kottabos"?

Why are there so many naked figures in vase iconography?

More Practical Tools for Students Powered by AI Study Helper

Making Your Study Simpler

For a drug that is a weak base with a pKa of 8.4, the predominant species at pH 7.4 will be:  Single choice