Question

The strongest Bronsted base in the following anion is: (a) \(\mathrm{CN}^{-}\) (b) \(\mathrm{Cl}^{-}\) (c) \(\mathrm{I}^{-}\) (d) \(\mathrm{Br}^{-}\)

Short answer

The strongest Bronsted base among the given anions is \text{(a) \text{CN}^-}.

Step-by-step solution

Understanding Bronsted Bases

A Bronsted base is a substance that accepts a proton (H+). An anion can be a Bronsted base if it has the ability to accept a proton. Generally, the strength of a Bronsted base is inversely related to the strength of its conjugate acid.

Identifying the Conjugate Acids

To determine the strength of the given anions as Bronsted bases, identify their conjugate acids. For CN-, it's HCN; for Cl-, it's HCl; for I-, it's HI; and for Br-, it's HBr.

Comparing Acid Strengths

The strength of the anions as bases depends on the strength of their conjugate acids. Weaker acids have stronger conjugate bases. Among HCN, HCl, HI, and HBr, HCN is the weakest acid.

Concluding the Strongest Bronsted Base

Since HCN is the weakest acid, its conjugate base, CN-, is the strongest Bronsted base among the options given.

Key concepts

Understanding Acid-Base Reactions

Acid-base reactions are fundamental processes in chemistry where an acid reacts with a base to form a salt and usually water. A basic understanding of acids and bases is crucial for students as these reactions are prevalent in both laboratory settings and everyday life.

In these reactions, an acid is characterized by its ability to donate a proton (a hydrogen ion, H+), while a base is defined by its ability to accept a proton. When an acid donates its proton, it becomes a conjugate base, and when a base accepts a proton, it transforms into a conjugate acid.

This transfer of protons is central to many biological and environmental systems. For example, our blood maintains a pH level through a delicate balance of acid-base reactions, and the acidity of soil can affect plant growth. Understanding the strength of acids and bases helps predict the direction and extent of chemical reactions and is a pivotal concept in chemistry education.

What are Conjugate Acid-Base Pairs?

Conjugate acid-base pairs are directly related to Bronsted-Lowry acid-base theory. They comprise two substances that transform into each other by the gain or loss of a proton.

To clarify this concept, consider the reaction between an acid such as hydrochloric acid (HCl) and a base such as ammonia (NH3). HCl donates a proton to NH3, creating the salt ammonium chloride (NH4Cl). In this process, NH3 becomes NH4+ (the conjugate acid of NH3), and HCl becomes Cl- (the conjugate base of HCl).

Key Points of Conjugate Pairs:

• The acid and its conjugate base differ by one proton.
• The base and its conjugate acid also differ by the presence of one proton.
• The strength of a conjugate base is inversely proportional to its conjugate acid.

This inverse relationship allows students to predict the result of acid-base reactions and understand the chemical behavior of substances within an acid-base context. Recognizing these pairs helps in balancing chemical equations and in designing chemical reactions for various applications.

Proton Acceptors in Chemistry

In chemistry, proton acceptors are better known as bases according to the Bronsted-Lowry theory. This theory expands on the concept of bases beyond substances that produce hydroxide ions in water, to include any species that can accept a proton.

A proton acceptor could be a simple ion like hydroxide (OH-), a larger molecule like ammonia (NH3), or even an anion like cyanide (CN-). The knack of these bases to accept protons makes them critically important in many chemical reactions, including buffering systems, which regulate pH in biological and environmental systems.

When analyzing different proton acceptors, the key characteristics to consider include: electron density, the stability of the base once it accepts the proton, and its ability to donate the accepted proton in the reverse reaction. These factors influence both the strength and reactivity of the base, making some proton acceptors like CN- much stronger bases compared to others such as Cl-.