The key difference between monoprotic and diprotic acid is that monoprotic acids are able to donate one hydrogen atom or proton to their aqueous solution, whereas diprotic acids are able to donate two hydrogen atoms or protons to their aqueous solution.
Monoprotic and diprotic acid compounds are two significant groups of acidic substances. These compounds are able to release protons to their aqueous solutions.
CONTENTS
1. Overview and Key Difference
2. What is a Monoprotic Acid
3. What is a Diprotic Acid
4. Monoprotic vs Diprotic Acid in Tabular Form
5. Summary – Monoprotic vs Diprotic Acid
What is a Monoprotic Acid?
A monoprotic acid is an acid composed of one ionizable hydrogen atom per molecule. This type of acid can donate only one proton or hydrogen atom from one molecule of acid to its aqueous solution. On the other hand, the acids that can donate more than one proton or hydrogen atom to the aqueous solution are known as polyprotic acids. These polyprotic acids can be further classified into groups based on the number of protons that are donated by each molecule. For example, if one acid molecule donates two protons or hydrogen atoms, it’s known as diprotic acid; if three are donated, it’s known as triprotic acid, and so on.
Typically, the electrical charge of a monoprotic acid can jump to one higher level before it can give the proton away. Moreover, we can predict that any acid having one hydrogen atom per molecule is a monoprotic acid. Therefore, all the single-hydrogen acids are monoprotic. However, not all monoprotic acids have only one hydrogen atom. For example, there can be compounds with more than one hydrogen atom per molecule, but they might be able to release only one hydrogen atom.
Furthermore, since only one hydrogen atom is donated, we can easily predict and calculate the pH of a monoprotic acid. In contrast, a monoprotic base can accept only one proton or hydrogen atom. Some examples of monoprotic acids include hydrochloric acid, nitric acid, acetic acid, etc.
What is a Diprotic Acid?
Diprotic acid molecules are acids that can donate two protons or hydrogen atoms per molecule. This type of acid is able to donate two protons to its aqueous solution. The opposite term for diprotic is monoprotic (meaning one proton or hydrogen atom per molecule). Some common examples of diprotic acids include sulfuric acid, carbonic acid, and oxalic acid.
Figure 01: Glycine is a Diprotic Acid (This curve shows the pH values at which the two protons are donated to the aqueous solution)
Diprotic acids are able to yield two H+ ions per acid molecule. Therefore, these acids can increase the hydrogen ion concentration of solutions and, thereby, decrease the pH value due to high acidity. We can identify a diprotic acid by titrating it with a sodium hydroxide solution having a known concentration.
What is the Difference Between Monoprotic and Diprotic Acid?
The key difference between monoprotic and diprotic acid is that monoprotic acids are able to donate one hydrogen atom or proton to their aqueous solution, whereas diprotic acids are able to donate two hydrogen atoms or protons to their aqueous solution. Hydrochloric acid, nitric acid, and acetic acid are examples of monoprotic acids, while sulfuric acid, carbonic acid, and oxalic acid are examples of diprotic acids. All in all, monoprotic acids are more acidic than diprotic acids.
The below infographic presents the differences between monoprotic and diprotic acid in tabular form for side-by-side comparison.
Summary – Monoprotic vs Diprotic Acid
The key difference between monoprotic and diprotic acid is that monoprotic acids are able to donate one hydrogen atom or proton to their aqueous solution, whereas diprotic acids are able to donate two hydrogen atoms or protons to their aqueous solution.
Reference:
1. Helmenstine, Anne Marie. “Monoprotic Acid Definition.” ThoughtCo, Aug. 27, 2020.
Image Courtesy:
1. “Glycine titration curve” By Zlir'a – Own work (CC0) via Commons Wikimedia
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