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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...

Titration of Polyprotic Acids with a Strong Base

Titration of Polyprotic Acids with a Strong Base

Titration of a polyprotic acid, which contains multiple ionizable protons, involves distinct dissociation steps, each with its own dissociation constant (Ka). Each successive Ka is weaker than the previous one. In the titration of a polyprotic acid like sulfurous acid with a strong base such as sodium hydroxide, the base first neutralizes the initial ionizable proton, forming an intermediate species (e.g., hydrogen sulfite ions). This step's titration curve resembles that of a weak monoprotic...

Types of Enols and Enolates

Types of Enols and Enolates

Aldehydes and ketones form enols, although only about 1% of the enol is present at the equilibrium for simple monocarbonyl compounds. The enol form is undetectable for acetaldehyde, present as only 1.5 × 10−4 % of acetone, and present as only 1.2% of cyclohexanone. Two kinds of regioisomeric enols are possible for unsymmetrical ketones, and their net composition is 1% at equilibrium. This instability is due to the lower bond energy of C=C than the C=O group. The additional instability of enols...

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...

Acidity and Basicity of Alcohols and Phenols

Acidity and Basicity of Alcohols and Phenols

Like water, alcohols are weak acids and bases. This is attributed to the polarization of the O–H bond making the hydrogen partially positive. Moreover, the electron pairs on the oxygen atom of alcohol make it both basic and nucleophilic. Protonation of an alcohol converts hydroxide, a poor leaving group, into water—a good one. The two acid–base equilibria corresponding to ethanol are depicted below.

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:

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Related Experiment Video

Updated: Jun 19, 2026

Sigma's Non-specific Protease Activity Assay - Casein as a Substrate

Sigma's Non-specific Protease Activity Assay - Casein as a Substrate

Published on: September 17, 2008

THE pH STABILITY OF PROTYROSINASE AND TYROSINASE.

T H Allen¹, A B Otis, J H Bodine

¹Zoological Laboratory, The State University of Iowa, Iowa City.

The Journal of General Physiology

|October 30, 2009

Summary

Protyrosinase is unstable above pH 7.30 and below pH 4.80. Tyrosinase is more stable, with stability ranges determined by pH, impacting enzyme research.

Area of Science:

Biochemistry
Enzymology

Background:

Understanding enzyme stability is crucial for biochemical applications.
Protyrosinase and tyrosinase are key enzymes in melanin biosynthesis.
Their pH-dependent stability influences their activity and utility.

Purpose of the Study:

To construct pH stability diagrams for protyrosinase and tyrosinase.
To determine the optimal pH ranges for the stability of both enzymes.
To investigate the pH-induced transformation of protyrosinase to tyrosinase.

Main Methods:

Enzyme assays were performed across a range of pH values.
Stability was assessed by measuring residual enzyme activity.
pH stability diagrams were generated to visualize stability profiles.

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The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes

The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes

Published on: May 25, 2018

Defining Substrate Specificities for Lipase and Phospholipase Candidates

Defining Substrate Specificities for Lipase and Phospholipase Candidates

Published on: November 23, 2016

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Last Updated: Jun 19, 2026

Sigma's Non-specific Protease Activity Assay - Casein as a Substrate

Sigma's Non-specific Protease Activity Assay - Casein as a Substrate

Published on: September 17, 2008

The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes

The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes

Published on: May 25, 2018

Defining Substrate Specificities for Lipase and Phospholipase Candidates

Defining Substrate Specificities for Lipase and Phospholipase Candidates

Published on: November 23, 2016

Main Results:

Protyrosinase demonstrates instability above pH 7.30, with irreversible conversion to tyrosinase beyond pH 9.30.
Protyrosinase is less stable at acidic pH, being destroyed below pH 4.80.
Tyrosinase exhibits greater stability, remaining unaffected until pH drops below 4.10.

Conclusions:

pH significantly impacts the stability and interconversion of protyrosinase and tyrosinase.
Protyrosinase has a narrower optimal pH range for stability compared to tyrosinase.
High pH-generated tyrosinase is comparable to tyrosinase produced via other methods.