Question

Define basicity of an acid. Give an example each for monobasic, dibasic and tribasic acids.

Short answer

Provide examples of monobasic, dibasic, and tribasic acids and explain the basicity of an acid. The basicity of an acid is the number of hydrogen ions (H+) it can donate or the number of hydroxyl ions (OH-) an acid can accept. Examples for each type of acid are: 1. Monobasic acid: Hydrochloric acid (HCl) is a monobasic acid that can donate only one hydrogen ion (H+) per molecule. 2. Dibasic acid: Sulfuric acid (H2SO4) is a dibasic acid that can donate two hydrogen ions (H+) per molecule. 3. Tribasic acid: Orthophosphoric acid (H3PO4) is a tribasic acid that can donate three hydrogen ions (H+) per molecule.

Step-by-step solution

Define Basicity of an Acid

The basicity of an acid is the number of hydrogen ions (H+) it can donate or the number of hydroxyl ions (OH-) that an acid can accept. In other words, it tells us how many moles of OH- ions are required to neutralize one mole of an acid.

Monobasic Acid Example

A monobasic acid is an acid that can donate only one hydrogen ion (H+) per molecule. An example of a monobasic acid is Hydrochloric acid (HCl). In a chemical reaction, HCl donates 1 proton to the solution: HCl(aq) -> H+(aq) + Cl^(-)(aq) For each molecule of HCl, only one H+ ion is formed.

Dibasic Acid Example

A dibasic acid is an acid that can donate two hydrogen ions (H+) per molecule. An example of a dibasic acid is Sulfuric acid (H2SO4). In a chemical reaction, H2SO4 donates 2 protons to the solution: H2SO4(aq) -> 2H+(aq) + SO4^2-(aq) For each molecule of H2SO4, two H+ ions are formed.

Tribasic Acid Example

A tribasic acid is an acid that can donate three hydrogen ions (H+) per molecule. An example of a tribasic acid is Orthophosphoric acid (H3PO4). In a chemical reaction, H3PO4 donates 3 protons to the solution: H3PO4(aq) -> 3H+(aq) + PO4^3-(aq) For each molecule of H3PO4, three H+ ions are formed.

Key concepts

Monobasic Acids

Monobasic acids are the simplest type of acids in terms of their ability to dissociate and donate protons (hydrogen ions, H+). As indicated by the prefix 'mono-', these acids only release one hydrogen ion per molecule during dissociation. Let's take a closer look at Hydrochloric acid (HCl), a commonly mentioned monobasic acid.

When HCl is dissolved in water, it undergoes a straightforward dissociation process:
\[ HCl(aq) \rightarrow H^+(aq) + Cl^-(aq) \]
Each HCl molecule provides one H+ to the solution, making the chemical equation a one-to-one ratio. The ability of HCl to donate a single proton makes it a strong acid, as it completely dissociates in water. This concept is crucial for understanding acid-base reactions and is particularly important in stoichiometric calculations involving neutralization reactions.

Dibasic Acids

Dibasic acids step up the complexity by being capable of releasing two hydrogen ions per molecule. The prefix 'di-' signifies the presence of two ionizable hydrogen atoms. A prime example is Sulfuric acid (H2SO4), which exhibits dibasic characteristics.

The dissociation of H2SO4 can be depicted as follows:
\[ H2SO4(aq) \rightarrow 2H^+(aq) + SO4^{2-}(aq) \]
What's important to note is that in the case of dibasic acids like H2SO4, the release of hydrogen ions may occur in stages. The first dissociation is often complete and strong, resulting in a full release of one H+, but the second H+ may release differently, sometimes incompletely or weaker, depending on the acid's strength and environmental conditions. Understanding these multi-stage dissociations is important for predicting the behavior of acids in different chemical environments and for calculating the pH of solutions.

Tribasic Acids

Tribasic acids are even more complex, with the ability to donate three hydrogen ions per molecule. They are recognized by the 'tri-' prefix. Orthophosphoric acid (H3PO4) serves as an exemplary tribasic acid, often used to illustrate this concept.

The stepwise dissociation of H3PO4 in water is shown here:
\[ H3PO4(aq) \rightarrow 3H^+(aq) + PO4^{3-}(aq) \]
As with dibasic acids, the dissociation of tribasic acids such as H3PO4 typically occurs in distinct stages. Each hydrogen ion is released sequentially, with the first ion generally dissociating more readily than the subsequent ones. This staged dissociation affects the acid's buffering capabilities and is a fundamental aspect of acid strength and the pH levels of solutions. Tribasic acids are crucial in the formation of phosphate buffers and play significant roles in biological systems and industrial processes.