Question

Define salt hydrolysis. Explain the hydrolysis of potassium carbonate by giving ionic equations.

Short answer

Answer: When potassium carbonate undergoes hydrolysis in water, the solution becomes more basic due to the increase in hydroxide ion (OH⁻) concentration. This occurs as the carbonate ion (CO₃²⁻) reacts with water molecules, forming bicarbonate ion (HCO₃⁻) and hydroxide ion (OH⁻).

Step-by-step solution

Define Salt Hydrolysis

Salt hydrolysis is a process in which a salt's ions interact with water molecules to form new compounds, resulting in a change in pH. This process typically occurs when an acidic or basic salt dissociates in water, causing the water molecules to either donate or accept protons, thus effectively altering the acidity or alkalinity of the solution.

Identify the ions in potassium carbonate

Potassium carbonate (K₂CO₃) is an ionic compound formed by the combination of two potassium ions (K⁺) and one carbonate ion (CO₃²⁻) in a crystal lattice. When dissolved in water, potassium carbonate dissociates into its individual ions: 2K⁺ and CO₃²⁻.

Write the hydrolysis ionic equations

When potassium carbonate is dissolved in water, the ions interact with water molecules. The potassium ions do not hydrolyze because they come from a strong base (potassium hydroxide, KOH) and do not react with water. However, the carbonate ion (CO₃²⁻) undergoes hydrolysis by accepting protons from water molecules: CO₃²⁻(aq) + H₂O(l) ⇌ HCO₃⁻(aq) + OH⁻(aq) In this reaction, the carbonate ion (CO₃²⁻) picks up a hydrogen ion (H⁺) from water, forming bicarbonate ion (HCO₃⁻) and hydroxide ion (OH⁻). The above equation shows that the hydrolysis of carbonate ion results in an increase in hydroxide ion concentration, causing the solution to become more basic.

Key concepts

Potassium Carbonate

Potassium carbonate, with the chemical formula \(K_2CO_3\), is a white, water-soluble salt. It is composed of two potassium ions \(K^{+}\) and one carbonate ion \(CO_3^{2-}\).
When potassium carbonate is dissolved in water, it dissociates into its constituent ions. These ions play a significant role in the behavior of the solution, particularly in processes like hydrolysis. Understanding the nature of these ions is crucial to grasping how potassium carbonate influences the pH of its solutions.

Ionic Equations

Ionic equations are important for understanding chemical reactions in solution. They show each ion's involvement in the reaction.
For potassium carbonate, the ionic equation illustrating its dissociation in water is:

• \(K_2CO_3 (s) \rightarrow 2K^+ (aq) + CO_3^{2-} (aq)\)

This equation tells us that potassium carbonate splits into two potassium ions and one carbonate ion when dissolved. These ionic forms are essential because they participate in further interactions, specifically hydrolysis. Ionic equations provide clarity on which ions are reactive and convey the exact process occurring in solution.

Hydrolysis Reaction

The hydrolysis reaction involves the interaction of ions with water, leading to a change in the solution's pH. In the context of potassium carbonate, hydrolysis occurs primarily with the carbonate ion \(CO_3^{2-}\).
The hydrolysis process can be understood through the equation:

• \(CO_3^{2-} (aq) + H_2O (l) \leftrightarrow HCO_3^- (aq) + OH^- (aq)\)

Here, the carbonate ion accepts a proton from a water molecule, producing bicarbonate \(HCO_3^-\) and hydroxide ions \(OH^-\). This exchange ultimately results in the formation of a more basic (alkaline) solution. Understanding this step by step enables students to appreciate how ionic interactions in water can modify the chemical environment.

Acidity and Alkalinity

Acidity and alkalinity refer to the concentration of hydrogen ions \(H^+\) and hydroxide ions \(OH^-\) in a solution, which determines its pH.
The hydrolysis of potassium carbonate markedly influences the alkalinity of the solution due to the production of hydroxide ions. When \(CO_3^{2-}\) ions pick up a proton from water, \(OH^-\) ions are released, raising the pH and increasing the solution's basic nature.
This process is crucial when considering the applications of potassium carbonate in various industries such as glass and ceramics, where control over pH is essential. Grasping how potassium carbonate influences acidity and alkalinity provides insight into its roles and applications.

Proton Transfer

Proton transfer is a central concept in understanding salt hydrolysis. It refers to the movement of hydrogen ions \(H^+\), often between ions and water molecules.
In the case of potassium carbonate hydrolysis, the carbonate ion \(CO_3^{2-}\) grabs a hydrogen ion from water, transforming into bicarbonate \(HCO_3^-\) and leaving behind a hydroxide ion \(OH^-\). This transfer is a key mechanism driving the reaction.
The increase in hydroxide ions, a result of proton transfer, elevates the basic quality of the solution. Recognizing proton transfer events is vital, as they deeply influence the dynamics of reactions in aqueous environments.