Question

Distinguish between a monoprotic, a diprotic, and a triprotic acid. Give an example of each.

Short answer

Monoprotic: HCl, Diprotic: H2SO4, Triprotic: H3PO4.

Step-by-step solution

Understand the Concept of Protic Acids

Protic acids are defined based on the number of protons (hydrogen ions) they can donate. Understanding the difference among monoprotic, diprotic, and triprotic acids is essential.

Identify Monoprotic Acids

Monoprotic acids are acids that can donate only one proton (H+ ion) per molecule. An example of a monoprotic acid is hydrochloric acid (HCl). When HCl dissolves in water, it releases one H+ ion.

Identify Diprotic Acids

Diprotic acids have the ability to donate two protons per molecule. An example of a diprotic acid is sulfuric acid (H2SO4). In water, H2SO4 can release two H+ ions in two steps.

Identify Triprotic Acids

Triprotic acids can donate three protons per molecule. An example of a triprotic acid is phosphoric acid (H3PO4). It releases three H+ ions in three steps when dissolved in water.

Key concepts

Monoprotic Acid

A monoprotic acid is an acid that donates only one proton (or hydrogen ion, H+) per molecule during the process of dissociation. This is the simplest form of protic acids. For example, when hydrogen chloride (HCl) dissociates in water, it releases one hydrogen ion (H+) and one chloride ion (Cl-). This process is represented by the equation:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
Monoprotic acids are often strong acids, meaning they dissociate completely in water. Common examples include:

• Hydrochloric acid (HCl)
• Nitric acid (HNO3)
• Acetic acid (CH3COOH) - although this one is a weak acid

Understanding monoprotic acids is crucial, as they serve as foundational examples when learning about more complex acids.

Diprotic Acid

Diprotic acids are acids that can donate two protons (H+ ions) per molecule. They release these protons in two different steps. For instance, sulfuric acid (H2SO4) is a common diprotic acid. When it dissolves in water, the dissociation occurs in two stages:
First dissociation step:
\[ \text{H}_2\text{SO}_4 \rightarrow \text{H}^+ + \text{HSO}_4^- \]
Second dissociation step:
\[ \text{HSO}_4^- \rightarrow \text{H}^+ + \text{SO}_4^{2-} \]
Diprotic acids have unique properties and behaviors, particularly in solutions because their second proton is often released at a different rate or under different conditions than the first. Other examples of diprotic acids include carbonic acid (H2CO3) and oxalic acid (H2C2O4).
Diprotic acids often have varied applications in industries and labs, making them important to understand.

Triprotic Acid

Triprotic acids can donate three protons per molecule. They go through three stages of dissociation. Phosphoric acid (H3PO4) is a classic example. In water, it dissociates in the following steps:
First dissociation step:
\[ \text{H}_3\text{PO}_4 \rightarrow \text{H}^+ + \text{H}_2\text{PO}_4^- \]
Second dissociation step:
\[ \text{H}_2\text{PO}_4^- \rightarrow \text{H}^+ + \text{HPO}_4^{2-} \]
Third dissociation step:
\[ \text{HPO}_4^{2-} \rightarrow \text{H}^+ + \text{PO}_4^{3-} \]
Each ionization step occurs successively, each removing an additional proton. The sequential release means that triprotic acids can create a variety of different ionic species in solution. Other triprotic acids include citric acid and boric acid. These acids are typically used in fertilizers and food products, reflecting their versatility in different fields.

Acid Donation

Acid donation refers to the process by which an acid releases its hydrogen ions (H+) into a solution. This behavior is critical in determining the acid’s strength and classification. There are key factors to consider:

• Strength of the Acid: Strong acids, like HCl, completely ionize in water, donating all available protons, while weak acids only partially ionize.
• Proton Availability: Monoprotic acids will donate one proton, diprotic acids two protons in two steps, and triprotic acids three protons in three steps.
• Environmental Influence: The pH and the nature of the solvent can influence how readily an acid donates its protons.

Understanding acid donation is crucial for predicting the behavior of acids in various chemical reactions and environments, affecting everything from biological systems to industrial processes.