Question

(a) Which of the following is the stronger Bronsted-Lowry acid, HBrO or HBr? (b) Which is the stronger Bronsted-Lowry base, \(F^{-}\) or \(C l^{-}\) ?

Short answer

HBrO is the stronger Bronsted-Lowry acid, and \(Cl^{-}\) is the stronger Bronsted-Lowry base.

Step-by-step solution

Analyze Acids

Let's begin by analyzing both HBrO and HBr. HBrO is a hypobromous acid, while HBr is a hydrogen bromide. The difference between the two acids is that HBrO has an oxygen atom connected to the bromine atom, while HBr does not. This difference in structure will impact their ability to donate protons.

Compare Acid Strength

The acidic strength can be compared by considering the stability of the resulting conjugate base. A stronger acid has a more stable conjugate base. When HBrO and HBr lose a proton, their conjugate bases will be BrO- and Br-, respectively. The stability of these ions can be determined by examining the electronegativity and size of the atoms involved. For HBrO, the negative charge is distributed between the oxygen and bromine atoms, whereas in HBr, the negative charge is localized on the bromine atom. Oxygen is more electronegative than bromine, so it can better stabilize the negative charge. Therefore, BrO- is more stable than Br-, making HBrO a stronger acid than HBr. **Answer:** HBrO is the stronger Bronsted-Lowry acid. **(b) Which is the stronger Bronsted-Lowry base, \(F^{-}\) or \(Cl^{-}\)?**

Analyze Bases

Let's analyze \(F^{-}\) and \(Cl^{-}\). Both are halide ions. When these anions act as bases, they would gain a proton, forming the corresponding conjugate acids HF and HCl, respectively. We will compare their basic strength based on the stability of their conjugate acids.

Compare Base Strength

The basic strength can be compared by considering the strength of the resulting conjugate acid. A weaker conjugate acid corresponds to a stronger base. Now, we need to compare the acid strength of HF and HCl. A stronger acid has a weaker anion, so the weaker acid will have a stronger anion, which will be the stronger base. Fluorine is more electronegative than chlorine and smaller in size. In general, acid strength increases with increasing electronegativity and decreasing size. Therefore, HF should be a stronger acid than HCl, which means that its anion, \(F^{-}\), is a weaker base. **Answer:** \(Cl^{-}\) is the stronger Bronsted-Lowry base.

Key concepts

Acid-Base Reactions

Understanding acid-base reactions is essential in the study of chemistry. An acid-base reaction involves a transfer of protons (H⁺) from acids to bases. In the Brønsted-Lowry theory, an acid is defined as a substance that can donate a proton, while a base is a substance that can accept a proton. When an acid donates a proton, it forms its conjugate base, and when a base accepts a proton, it forms its conjugate acid.

The strength of an acid or base depends on its ability to donate or accept protons, which is directly related to the stability of its conjugate base or acid. For instance, when HBrO loses a proton to become BrO^-, it is considered a stronger acid if BrO^- is more stable. Similarly, when F^- gains a proton to form HF, F^- is a weaker base if HF is a stronger acid. Acid-base reactions are therefore equilibrium processes, where the direction of the reaction favors the formation of the weaker acid and base from the stronger counterparts.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are directly related to the concept of acid-base reactions. In such a pair, the acid and base differ by the presence or absence of a proton. Every acid has a corresponding conjugate base that is formed when the acid donates a proton, and every base has a corresponding conjugate acid that is formed when the base accepts a proton.

Let's consider the reaction between HBrO and HBr once again. HBrO, when donating a proton, becomes BrO^-, which is its conjugate base. HBr, on the other hand, donates a proton to become Br^-, its conjugate base. An important aspect of these pairs is that the strength of an acid is inversely related to the strength of its conjugate base. This inverse relationship is a crucial factor in predicting the direction of acid-base reactions and the equilibrium state. When comparing conjugate bases, BrO^- and Br^-, we see that the more stable conjugate base, which has delocalized charges and greater electronegativity, often comes from the stronger acid.

Electronegativity and Acid Strength

Electronegativity plays a significant role in determining the strength of acids and bases. Electronegativity is the measure of an atom's ability to attract electrons in a bond. In the context of acidity, the more electronegative an atom attached to a proton is, the more it can stabilize the negative charge after the proton is donated. As a result, acids with highly electronegative atoms, such as fluoride in HF, are generally stronger.

In the comparison between HBrO and HBr, the oxygen in HBrO has a high electronegativity which helps stabilize the negative charge on its conjugate base BrO^-. This stabilization makes HBrO a stronger acid. Similarly, looking at the base strength of F^- compared to Cl^-, F^- is less basic than Cl^- because fluorine is more electronegative and thus forms a stronger acid when it accepts a proton (HF). This understanding of electronegativity and acid strength helps predict and explain the behavior of different substances in acid-base reactions.