Difference Between Amphiprotic and Polyprotic

The key difference between amphiprotic and polyprotic is that amphiprotic refers to the ability to both donate and accept protons, whereas polyprotic refers to the ability to donate or accept more than one proton.

The terms amphiprotic and polyprotic are used as adjectives to describe chemical compounds. These terms describe the ability or inability to donate/accept protons. In these terms, “-protic” means protons, which are the H⁺ ions that can be removed from a chemical compound.

CONTENTS

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

What is Amphiprotic?

Amphiprotic refers to the ability of a chemical compound to donate or accept protons. Specifically, amphiprotic chemical compounds are able to both donate and accept protons to or from other compounds. In this context, we refer to H⁺ ions as protons. Amphiprotic compounds can be either an acid or a base. Therefore, these compounds have both acidic and basic characteristics.

Examples for amphiprotic chemical compounds include amino acids, which contains amine groups and carboxylic groups, proteins which are made up of amino acids, and water, which contains protons and lone electron pairs on oxygen atom which can act as a proton acceptor.

What is Polyprotic?

Polyprotic refers to the ability of a chemical compound to donate more than one proton. Here, “poly” means many and “-protic” means proton donating. There are two types of polyprotic chemical species as polyprotic acids and polyprotic bases.

Polyprotic acids are capable of releasing more than one proton per molecule. Polyprotic bases are chemical species that are capable of accepting more than one proton per molecule. For example, sulfuric acid, phosphoric acid, carbonic acid, sulfurous acid, etc. are polyprotic acids. Phosphate ion, sulfate ion, carbonate ion, etc. are examples for polyprotic bases.

What is the Difference Between Amphiprotic and Polyprotic?

The terms amphiprotic and polyprotic refer to the removal of protons from chemical compounds. The key difference between amphiprotic and polyprotic is that amphiprotic refers to the ability to both donate and accept protons, whereas polyprotic refers to the ability to donate or accept more than one proton.

Moreover, amphiprotic chemical species can donate or accept one or more protons per molecule whereas polyprotic chemical species can donate or accept more than one proton per molecule. Some examples for amphiprotic chemical compounds include amino acids, proteins and water, while examples for polyprotic chemical species include phosphoric acid, sulfurous acid, sulfuric acid, and phosphate ion.

The following table summarizes the difference between amphiprotic and polyprotic chemical species.

Summary – Amphiprotic vs Polyprotic

The terms amphiprotic and polyprotic refer to the removal of protons from chemical compounds. The key difference between amphiprotic and polyprotic is that amphiprotic refers to the ability to both donate and accept protons whereas polyprotic refers to the ability to donate or accept more than one proton. Some examples for amphiprotic chemical compounds include amino acids, proteins and water while some examples for polyprotic chemical species include phosphoric acid, sulfurous acid, sulfuric acid, and phosphate ion.

Reference:

1. Helmenstine, Anne Marie. “Amphiprotic Definition in Chemistry.” ThoughtCo, Feb. 11, 2020, Available here.
2. “11.11: Amphiprotic Species.” Chemistry LibreTexts, Libretexts, 7 Feb. 2020, Available here.
3. “Polyprotic Acids And Bases.” Chemistry LibreTexts, Libretexts, 5 June 2019, Available here.

Image Courtesy:

1. “Amino Acid ball” By GYassineMrabetTalk✉This W3C-unspecified vector image was created with Inkscape. – Own work (Public Domain) via Commons Wikimedia
2. “Phosphoric3” By Petergans (talk) – A species distribution diagram as described in Section 2.4, Public Domain) via Commons Wikimedia