Problem 23 - Chemistry and Chemical Reactivity

Question

Dissolving \(\mathrm{K}_{2} \mathrm{CO}_{3}\) in water gives a basic solution. Write a balanced equation showing how this can occur.

Step-by-Step Solution

Answer

The balanced equation: \( \mathrm{K}_2\mathrm{CO}_3(s) + \mathrm{H}_2\mathrm{O}(l) \rightarrow 2\mathrm{K}^+(aq) + \mathrm{HCO}_3^-(aq) + \mathrm{OH}^-(aq) \).

Step 1: Identify Substance Dissolving

We start with the compound potassium carbonate, which is represented by the chemical formula \(\mathrm{K}_2\mathrm{CO}_3\). This compound will dissolve in water.

Step 2: Dissolution in Water

When potassium carbonate dissolves in water, it dissociates into its ions. The chemical equation for this dissolution is: \[ \mathrm{K}_2\mathrm{CO}_3(s) \rightarrow 2\mathrm{K}^+(aq) + \mathrm{CO}_3^{2-}(aq) \] where \(\mathrm{K}^+\) is the potassium ion and \(\mathrm{CO}_3^{2-}\) is the carbonate ion.

Step 3: Identify Basic Nature

The carbonate ion \(\mathrm{CO}_3^{2-}\) reacts with water to form a weak acid and a hydroxide ion. The reaction is: \[ \mathrm{CO}_3^{2-}(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{HCO}_3^-(aq) + \mathrm{OH}^-(aq) \] the \(\mathrm{OH}^-\) ion makes the solution basic.

Step 4: Overall Reaction

Combining the two reactions from steps 2 and 3, the full process occurring in solution is as follows: \[ \mathrm{K}_2\mathrm{CO}_3(s) + \mathrm{H}_2\mathrm{O}(l) \rightarrow 2\mathrm{K}^+(aq) + \mathrm{HCO}_3^-(aq) + \mathrm{OH}^-(aq) \]

Key Concepts

Potassium Carbonate

Potassium carbonate, known chemically as \(\mathrm{K}_2\mathrm{CO}_3\), is a white, water-soluble salt. It is comprised of two potassium (\(\mathrm{K}^+\)) ions and one carbonate (\(\mathrm{CO}_3^{2-}\)) ion. This compound is commonly used in applications such as glass making, soap production, and as a buffering agent in laboratories.

When potassium carbonate is introduced to water, it fully dissolves, breaking apart into its constituent ions. This process is important because it sets the stage for subsequent reactions that occur in solution, giving rise to particular characteristics, such as the solution's basic nature. Understanding this dissolution process is key to predicting the behavior of \(\mathrm{K}_2\mathrm{CO}_3\) in aqueous environments.

Dissolution

Dissolution is the process by which a solute— such as potassium carbonate— dissociates into ions when mixed with a solvent like water. For \(\mathrm{K}_2\mathrm{CO}_3\), the dissolution can be represented by the chemical equation:

• \(\mathrm{K}_2\mathrm{CO}_3(s) \rightarrow 2\mathrm{K}^+(aq) + \mathrm{CO}_3^{2-}(aq)\)

This equation shows that the solid potassium carbonate separates into two potassium ions and one carbonate ion upon dissolving in water.

Such dissociation is crucial for further reactions and often influences the characteristics of the solution. In the context of potassium carbonate, this dissolution leads to a basic solution, which is significant, especially in chemical applications and studies.
The knowledge about dissolution helps predict how compounds will behave when going into solutions and is foundational in chemistry.

Carbonate Ion

The carbonate ion \(\mathrm{CO}_3^{2-}\) plays a critical role once potassium carbonate dissolves in water. This ion is a polyatomic anion, meaning it carries a negative charge and consists of more than one atom. In solution, one of its primary actions is to interact with water molecules.

Through this interaction, the carbonate ion can react with water to form bicarbonate \(\mathrm{HCO}_3^-\) and hydroxide ions \(\mathrm{OH}^-\), as shown in the reaction:

• \(\mathrm{CO}_3^{2-}(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{HCO}_3^-(aq) + \mathrm{OH}^-(aq)\)

This equilibrium reaction is key because it explains how a seemingly neutral carbonate solution can become basic. The production of \(\mathrm{OH}^-\) ions in water results in this property, which is why understanding the behavior of the carbonate ion is so vital.

Hydroxide Ion

The presence of the hydroxide ion \(\mathrm{OH}^-\) in a solution is what gives it a basic nature. When \(\mathrm{K}_2\mathrm{CO}_3\) dissolves in water, not only do the constituent ions form, but reactions occur that generate \(\mathrm{OH}^-\) ions.

This ion, being negatively charged, is a strong indicator of basicity. It arises in the reaction where the carbonate ion reacts with water to form both bicarbonate and hydroxide ions.

• \(\mathrm{CO}_3^{2-}(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{HCO}_3^-(aq) + \mathrm{OH}^-(aq)\)

The hydroxide ion's presence increases the pH of the solution, a simple numerical measure of how "basic" or "acidic" a solution is.
The more \(\mathrm{OH}^-\) ions, the higher the pH, illustrating the basic nature of the potassium carbonate solution. Understanding hydroxide ions is crucial for interpreting reactions in aqueous chemistry, especially reactions involving salts.