Problem 269 - A Complete Resource Book in Chemistry for JEE Main

Question

The conjugate base of \(\mathrm{OH}^{-}\)is (a) \(\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{O}^{2}\) (c) \(\mathrm{O}^{-}\) (d) \(\mathrm{O}_{2}\)

Step-by-Step Solution

Answer

The conjugate base of \\(\mathrm{OH}^{-}\\) is (b) \\(\mathrm{O}^{2-}\\).

Step 1: Understanding Conjugate Base and Acids

A conjugate base is what remains after an acid loses a proton (H⁺) in an acid-base reaction. Conversely, a conjugate acid is what forms when a base gains a proton.

Step 2: Identifying the Acid-Base Pair

In this problem, we start with the hydroxide ion, \(\mathrm{OH}^{-}\). To find its conjugate base, we need to consider what forms when it loses a proton (H⁺).

Step 3: Removing a Proton from \\(\mathrm{OH}^{-}\\)

The hydroxide ion \(\mathrm{OH}^{-}\) needs to lose a proton to become its conjugate base. When it loses \(H^{+}\), it forms \(\mathrm{O}^{2-}\).

Step 4: Selecting the Correct Option

From the options provided: (a) \(\mathrm{H}_2 \mathrm{O}\), (b) \(\mathrm{O}^{2-}\), (c) \(\mathrm{O}^{-}\), and (d) \(\mathrm{O}_2\), we see that the correct conjugate base of \(\mathrm{OH}^{-}\) is \(\mathrm{O}^{2-}\).

Key Concepts

Conjugate Acids and Bases

In chemistry, the concept of conjugate acids and bases helps us understand acid-base reactions better. When an acid and a base react, they exchange protons (H⁺ ions) in a process known as proton transfer. This reaction results in the formation of conjugate pairs.

• A conjugate base is formed when an acid loses a proton. For example, when hydrochloric acid ( HCl ) loses a proton, it forms its conjugate base, the chloride ion ( Cl^{-} ).
• Conversely, a conjugate acid is formed when a base gains a proton. For instance, when ammonia ( NH_3 ) gains a proton; it forms ammonium ( NH_4^{+} ).

This interplay between acids and bases is fundamental to understanding how substances behave and react with each other in different environments, allowing chemists to predict possible reaction products.

Hydroxide Ion

The hydroxide ion ( OH^{-} ) is a base commonly involved in acid-base reactions. It consists of one oxygen and one hydrogen atom with a negative charge.

• The negative charge on the hydroxide ion is responsible for its strong ability to act as a base by accepting protons from acids.
• This makes it a common participant in neutralizing acid reactions, where it forms water. For instance, when hydrochloric acid (HCl) reacts with hydroxide ions ( OH^{-} ), the products are water ( H_2O ) and chloride ions ( Cl^{-} ).

Understanding the hydroxide ion's role in chemistry is crucial for predicting reaction outcomes and manipulating chemical processes in industries and laboratories.

Acid-Base Reactions

Acid-base reactions are chemical reactions that occur when acids and bases interact, typically resulting in the exchange of protons. These reactions are fundamental in many processes, including digestion, industrial manufacturing, and even environmental systems.

• In these reactions, the acid donates a proton to the base. This donation creates two new species: a conjugate acid and a conjugate base.
• An example of an acid-base reaction is the reaction between sulfuric acid ( H_2SO_4 ) and sodium hydroxide ( NaOH ). Here, sodium hydroxide (a base) reacts with sulfuric acid (an acid) to produce water ( H_2O ) and sodium sulfate ( Na_2SO_4 ).

Acid-base reactions are essential to both biological and chemical systems, and understanding them allows chemists to predict and control the properties of the substances involved. They play a critical role in various phenomena, including pH balance, metabolic pathways, and the workings of batteries.