Problem 16 - A Complete Resource Book in Chemistry for JEE Main

Question

When \(\mathrm{K}_{2} \mathrm{O}\) is added to water, the solution is basic because it contains a significant concentration of (a) \(\mathrm{OH}^{-}\) (b) \(\mathrm{K}^{+}\) (c) \(\mathrm{O}^{3}\) (d) \(\mathrm{O}_{2}^{2-}\)

Step-by-Step Solution

Answer

The solution is basic because it contains a significant concentration of (a) {OH^-}.

Step 1: Understanding Potassium Oxide Reaction with Water

Potassium oxide ({K_2O}) is a metal oxide that reacts with water to form a basic solution. The key to solving this problem is to determine the products of this reaction.

Step 2: Chemical Equation Formation

When {K_2O} is added to water ({H_2O}), it dissolves and reacts to form potassium hydroxide ({KOH}). The balanced chemical equation for the reaction is: {K_2O + H_2O ightarrow 2KOH}.

Step 3: Analyzing the Product

The key product of the reaction is potassium hydroxide ({KOH}), which is an ionic compound that dissociates in water. When it dissociates, it forms potassium ions ({K^+}) and hydroxide ions ({OH^-}).

Step 4: Determining the Basic Component

The basic nature of a solution is due to the presence of hydroxide ions ({OH^-}). Since the solution contains a significant concentration of {OH^-} ions, the solution is basic.

Key Concepts

Potassium Oxide

Potassium oxide, with the chemical formula \(\mathrm{K}_2\mathrm{O}\), is an example of a basic oxide. Basic oxides typically consist of a metal element combined with oxygen. This compound is highly reactive, especially when it comes into contact with water.
When \(\mathrm{K}_2\mathrm{O}\) encounters water, it immediately reacts to form potassium hydroxide \(\mathrm{KOH}\). This transformation can be represented by the balanced chemical equation: \[\mathrm{K}_2\mathrm{O} + \mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{KOH}\].
In this reaction, each molecule of potassium oxide combines with a molecule of water, producing two molecules of potassium hydroxide. The swift reaction highlights the high reactivity of potassium oxide in aqueous environments.

• This compound is considered basic because its reaction product leads to the formation of a base in water.
• Potassium oxide acts as a source of hydroxide ions once it dissolves.

Basic Solutions

Basic solutions—often referred to as alkaline solutions—are characterized by their high pH levels, which are greater than 7. This elevated pH level is a result of the concentration of hydroxide ions \(\mathrm{OH}^-\) in the solution.
The presence of these ions determines the basic nature by making the solution capable of accepting protons. Basic solutions can be recognized by their slippery feel and the ability to turn red litmus paper blue.
When potassium hydroxide \(\mathrm{KOH}\), formed from the reaction of potassium oxide and water, dissolves in water, it dissociates completely. This dissociation enhances the concentration of hydroxide ions, thereby increasing the pH.

• By increasing hydroxide ions, the solution becomes basic.
• Basic solutions play a vital role in chemical processes that neutralize acids.

Hydroxide Ions

Hydroxide ions \(\mathrm{OH}^-\) are negatively charged and are crucial in defining the characteristics of a basic solution. These ions result from the dissociation of bases in water, such as \(\mathrm{KOH}\).
The more hydroxide ions present, the more alkaline the solution becomes. This is because hydroxide ions readily accept protons, a key property contributing to their basicity.
In the context of the reaction between potassium oxide and water, the hydroxide ions stem from the dissociation of potassium hydroxide.

• Hydroxide ions are responsible for the basic result of \(\mathrm{K}_2\mathrm{O}\) in water.
• They serve a crucial function in various applications including neutralizing acids and in the formulation of soaps and cleaning agents.

Understanding hydroxide ions is essential in grasping why certain solutions behave as they do, especially in reactions involving metal oxides.