Difference Between Ampholyte and Amphoteric

The key difference between ampholyte and amphoteric is that the term amphoteric means the ability of a molecule to act as an acid or a base whereas an ampholyte is a molecule, which is amphoteric.

We come across molecules, which we categorize as basic, acidic or neutral. Basic solutions show pH values higher than 7 and the acidic solutions show pH values, which are lower than 7. Solutions having pH value 7 are the neutral solutions. There are some molecules, which differ from this normal categorization. Ampholytes are one such molecule. They have both acidic and basic chemical nature.

CONTENTS

1. Overview and Key Difference
2. What is Ampholyte
3. What is Amphoteric
4. Side by Side Comparison – Ampholyte vs Amphoteric in Tabular Form
5. Summary

What is Ampholyte?

An ampholyte is a molecule having both basic and acidic groups. The best and most widely occurring common example for ampholyte is amino acids. We know that all the amino acids have –COOH, -NH₂ groups and a –H bonded to a carbon. The carboxylic group (-COOH) acts as the acidic group in the amino acid, and the amine (-NH₂) group acts as the basic group. Other than these, there is a –R group in every amino acid. The R group differs from one amino acid to another. The simplest amino acid with R group being H is glycine.

However, the R group in some amino acids contains additional carboxylic groups or amine groups. For instance, lysine, histidine, and arginine are amino acids having additional amine groups. And aspartic acids, glutamic acids contain additional carboxylic groups. Further, some of them contain –OH groups, which can act as a base or acid under certain circumstances (tyrosine). Due to both acidic and basic groups, they generally have at least two pKa values (if there is more than one –NH₂ group or –COOH group, then there will be more than two pKa values). Therefore, the titration curves of ampholytes are complex than the normal titration curves.

Occurrence

In various systems, ampholytes occur in various charged forms depending on the pH. For instance, in an acidic solution, the amine group of the amino acids will occur in the positively charged from, and the carboxyl group will exist as –COOH. In a basic pH solution, the carboxyl group will exist in the form of carboxylate anion (-COO-), and the amino group will be present as –NH₂.

In human bodies, pH is close to 7.4. Hence, in this pH, amino acids present as zwitterions. Here, the amino group undergoes protonation and has a positive charge, whereas the carboxyl group has a negative charge. Therefore, the net charge of the molecule is zero. At this point, the molecule reaches its isoelectric point.

What is Amphoteric?

The term amphoteric means the ability of a molecule, ion or any other complex compound to act as a base and an acid. There are some molecules, which have both these properties under certain circumstances. Moreover, there are some metal oxides and hydroxides, which are amphoteric.

For instance, zinc oxide (ZnO), aluminum oxide (Al₂O₃), aluminum hydroxide (Al(OH)₃), and lead oxides are amphoteric. In acidic mediums, they act as bases, and in basic mediums, they act as acids. The most common and well known amphoteric molecule are amino acids, which we can observe in all the biological systems.

What is the Difference Between Ampholyte and Amphoteric?

An ampholyte is a molecule having both basic and acidic groups and the term amphoteric means the ability of a molecule, ion or any other complex compound to act as a base and an acid. The key difference between ampholyte and amphoteric is that the term amphoteric means the ability of a molecule to act as an acid or a base whereas an ampholyte is a molecule which is amphoteric.

Furthermore, Zinc oxide, aluminum oxide, aluminum hydroxide, and lead oxides are amphoteric, which have different behaviors in acidic and basic solutions. However, these are not ampholytes because they do not have acidic and basic groups in those molecules. Anyway, amino acid is an ampholyte, which has both acidic and basic groups present in one molecule. Hence, it is amphoteric as well.

Summary – Ampholyte vs Amphoteric

Amphoteric means the ability of a molecule to act as an acid or a base. Ampholytes are molecules which are amphoteric. Therefore, ampholytes have both acidic and basic groups. Hence, the key difference between ampholyte and amphoteric is that the term amphoteric means the ability of a molecule to act as an acid or a base whereas an ampholyte is a molecule which is amphoteric.

Reference:

1. Helmenstine, Anne Marie, Ph.D. “Amphoteric Definition and Examples.” ThoughtCo, Jun. 22, 2018. Available here
2. Libretexts. “Amphoteric.” Chemistry LibreTexts, National Science Foundation, 20 Feb. 2017. Available here  

Image Courtesy:

1.”Amino acid zwitterions”By TimVickersvector (CC BY 3.0) via Commons Wikimedia 
2.”Amphoteric”By Tem5psu – Own work, (CC BY-SA 3.0) via Commons Wikimedia