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Acid and Bases: Ka, pKa, and Relative Strengths

Acid and Bases: K_a, pK_a, and Relative Strengths

This lesson delves into a critical aspect of the relative strengths of acids and bases. The strength of an acid is evaluated by the acid dissociation into its conjugate base and a hydronium ion in water. The complete dissociation of a strong acid is confirmed with a very high concentration of hydronium ions. As a result, an incomplete dissociation process affirms a weak acid. Therefore, the equilibrium is in the forward direction for strong acids and backward for weak acids in these reactions.

Weak Base Solutions

Weak Base Solutions

Some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and so are classified as weak bases. These types of compounds are also abundant in nature and important commodities in various technologies. For example, global production of the weak base ammonia is typically well over 100 metric tons annually, being widely used as an agricultural fertilizer, a raw material for chemical synthesis of other...

Polyprotic Acids

Polyprotic Acids

Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:

Extraction: Effects of pH

Extraction: Effects of pH

Consider a neutral form of an amine, B, with a partition coefficient, K, in a liquid mixture containing organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes, and the charged form is usually more soluble in the aqueous phase. Suppose the conjugate acid form of the amine is soluble only in the aqueous phase while the base form is soluble in both phases. Then the distribution coefficient, D, can be given as the ratio of amine concentration in the...

Titration of a Polyprotic Acid

Titration of a Polyprotic Acid

A polyprotic acid contains more than one ionizable hydrogen and undergoes a stepwise ionization process. If the acid dissociation constants of the ionizable protons differ sufficiently from each other, then the titration curve for such polyprotic acid generates a distinct equivalence point for each of its ionizable hydrogens. Therefore, titration of a diprotic acid results in the formation of two equivalence points, whereas the titration of a triprotic acid results in the formation of three...

Solvating Effects

Solvating Effects

An understanding of the solvating effect helps rationalize the relation between solvation and acidity of the compound. In addition, this also explains the relative stability of conjugate bases for compounds with different pKa values. This lesson details, in-depth, the principle of solvating effects. The strength of an acid and the stability of its corresponding conjugate base are determined using pKa values. This observed relationship is a consequence of solvation, which is the interaction...

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Related Experiment Video

Updated: Jun 20, 2026

Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability

Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability

Published on: April 2, 2015

Predicting pKa.

Adam C Lee¹, Gordon M Crippen

¹Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109, USA.

Journal of Chemical Information and Modeling

|August 26, 2009

Summary

This summary is machine-generated.

Understanding the dissociation constant (pK(a)) is crucial for drug pharmacokinetics and molecular interactions. This study reviews experimental pK(a) data sources and analyzes current prediction methods for accuracy and validity.

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Determination of the Gas-phase Acidities of Oligopeptides

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Published on: June 24, 2013

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Last Updated: Jun 20, 2026

Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability

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Determination of the Gas-phase Acidities of Oligopeptides

Determination of the Gas-phase Acidities of Oligopeptides

Published on: June 24, 2013

Area of Science:

Biochemistry
Chemical Biology
Pharmacology

Background:

Physicochemical properties, specifically dissociation constants (pK(a)), are fundamental to understanding molecular behavior.
pK(a) values significantly influence drug pharmacokinetics and the interactions of proteins with other molecules.
Accurate pK(a) determination is essential for drug design and biological systems analysis.

Purpose of the Study:

To survey existing sources of experimental pK(a) values for small molecules and macromolecules.
To critically analyze current computational methods for predicting pK(a) values.
To evaluate the scope, statistical validity, predictive power, and accuracy of these prediction methods.

Main Methods:

Literature review of experimental pK(a) databases and resources.
Systematic analysis of various computational algorithms used for pK(a) prediction.
Comparative assessment of prediction methods based on statistical metrics and accuracy.

Main Results:

Identification of key experimental pK(a) data repositories.
Evaluation of the strengths and limitations of different pK(a) prediction approaches.
Assessment of the accuracy and reliability of current predictive models.

Conclusions:

The accurate prediction of pK(a) values remains a significant challenge in computational chemistry and drug discovery.
Understanding the limitations of existing prediction methods is vital for their appropriate application.
Further development of robust and accurate pK(a) prediction tools is needed.