Question

What is an autoionization reaction? Write equations for the autoionization reactions of \(\mathrm{H}_{2} \mathrm{O}\) and of \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Short answer

Autoionization is a reaction where molecules self-ionize.Equations: \[ 2\textrm{H}_2O = \textrm{H}_3O^+ + \textrm{OH}^- \]\[ 2\textrm{H}_2SO_4 = \textrm{HSO}_4^- + \textrm{H}_3SO_4^+ \]

Step-by-step solution

Understand Autoionization

Autoionization is a process where a molecule spontaneously ionizes into ions without the addition of any external substances. It usually involves the transfer of a proton (H⁺) between two identical molecules.

Autoionization of Water (\textrm{H}_2O)

For water, the autoionization reaction involves two water molecules exchanging a proton. The equation for this reaction is:\[ 2\textrm{H}_2O \rightleftharpoons \textrm{H}_3O^+ + \textrm{OH}^- \]

Identify Autoionization of Sulfuric Acid (\textrm{H}_2SO_4)

Sulfuric acid can also undergo autoionization. The reaction involves the transfer of a proton from one \textrm{H}_2SO_4 molecule to another, forming \textrm{HSO}_4^- and \textrm{H}_3SO_4^+. The equation for this reaction is:\[ 2\textrm{H}_2SO_4 \rightleftharpoons \textrm{HSO}_4^- + \textrm{H}_3SO_4^+ \]

Key concepts

proton transfer

Proton transfer is a fundamental concept in chemistry, especially in reactions involving acids and bases. It essentially refers to the movement of a proton (H⁺) from one molecule to another. This process is key to understanding how autoionization works.
An example of proton transfer is the autoionization of water molecules where one water molecule donates a proton to another.
This event results in the formation of hydronium (H₃O⁺) and hydroxide (OH⁻) ions. Proton transfer reactions are essential components in many biological and chemical processes.

water autoionization

Water (H₂O) is unique in its ability to autoionize, which means it can ionize itself without any external substances.
During autoionization, two water molecules interact by transferring a proton from one to the other. The chemical equation representing this reaction is:
\[2\textrm{H}_2O \rightleftharpoons \textrm{H}_3O^+ + \textrm{OH}^-\]
In this reaction:

• One water molecule acts as a proton donor, forming hydroxide (OH⁻) ions.
• The other water molecule accepts the proton and becomes a hydronium ion (H₃O⁺).

Understanding this equation is crucial for grasping the concept of pH and acid-base equilibria in water.

sulfuric acid autoionization

Sulfuric acid (H₂SO₄) can also undergo autoionization, though it behaves differently compared to water.
In sulfuric acid, one molecule transfers a proton to another. This process results in the formation of hydrogen sulfate (\textrm{HSO}_4^-) and tri-hydrogen sulfate (\textrm{H}_3SO_4^+) ions. The chemical equation for this reaction is:
\[2\textrm{H}_2SO_4 \rightleftharpoons \textrm{HSO}_4^- + \textrm{H}_3SO_4^+\]
In this reaction:

• One \textrm{H}_2SO_4 molecule donates a proton.
• The other \textrm{H}_2SO_4 molecule accepts the proton, resulting in an ion pair.

This process is similar to water autoionization but takes place between sulfuric acid molecules. It’s important for students to understand that autoionization reactions are not just limited to water but can also occur in other compounds like sulfuric acid.