Question

Determine whether each pair is a conjugate acid-base pair. (a) \(\mathrm{NH}_{3}, \mathrm{NH}_{4}{ }^{+}\) (b) \(\mathrm{HCl}, \mathrm{HBr}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}, \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) (d) \(\mathrm{HCO}_{3}^{-}, \mathrm{NO}_{3}^{-}\)

Short answer

Conjugate acid-base pairs are: (a) \(NH_3, NH_4^+)\, (c) \(C_2H_3O_2^-, HC_2H_3O_2)\. Pairs (b) \(HCl, HBr)\ and (d) \(HCO_3^-, NO_3^-)\ are not conjugate acid-base pairs.

Step-by-step solution

Understanding Acid-Base Conjugate Pairs

A conjugate acid-base pair consists of two species that differ by the presence or absence of a proton (H+). The acid member of the pair has one extra proton compared to its conjugate base.

Evaluate Pair (a) \(NH_3, NH_4^+)\

Compare the two formulas to determine if they differ by one proton. \(NH_3\) can accept a proton (H+) to become \(NH_4^+\), therefore, they form a conjugate acid-base pair with \(NH_3\) as the base and \(NH_4^+\) as the acid.

Evaluate Pair (b) \(HCl, HBr)\

Examine the two species for a difference of one proton. Hydrochloric acid (HCl) and hydrobromic acid (HBr) are both acids. They do not form a conjugate pair as they are not one proton apart.

Evaluate Pair (c) \(C_2H_3O_2^-, HC_2H_3O_2)\

Check if the addition or removal of a proton connects the two chemical species. Acetate ion \(C_2H_3O_2^-\) can gain a proton to become acetic acid \(HC_2H_3O_2\), so they are a conjugate acid-base pair, with \(C_2H_3O_2^-\) as the base and \(HC_2H_3O_2\) as the acid.

Evaluate Pair (d) \(HCO_3^-, NO_3^-)\

Determine if these species differ by a proton. Bicarbonate ion \(HCO_3^-\) and nitrate ion \(NO_3^-\) cannot be a conjugate acid-base pair since there is no transfer of a proton between them.

Key concepts

Acid-Base Chemistry

Acid-base chemistry is a fundamental concept in chemistry that deals with the reactions between acids and bases.

Acids are substances that can donate protons (hydrogen ions, represented as H+), whereas bases are substances that can accept protons.

The strength of an acid or base is often described by the pH scale, which measures the concentration of hydrogen ions in a solution. A low pH indicates a strong acid, while a high pH denotes a strong base.

It's essential to recognize conjugate acid-base pairs, which are specific pairs of molecules or ions that transform into each other by gaining or losing a proton. This concept is vital for understanding the nuances of chemical reactions and the behavior of substances in different environments.

Proton Transfer Reactions

Proton transfer reactions, also known as acid-base reactions, are processes where a proton is relocated from one chemical species to another.

These reactions are crucial in various biochemical and industrial processes and are governed by the principle known as the Bronsted-Lowry theory. According to this theory, an acid is defined as a proton donor, and a base as a proton acceptor.

Understanding the direction of proton transfer can help predict the outcome of a chemical reaction. For example, if a substance with a tendency to donate a proton (an acid) reacts with one that readily accepts protons (a base), a proton transfer reaction will occur, leading to new products and the formation of a conjugate pair.

Chemical Species Difference

The term 'chemical species' refers to different forms of matter, such as atoms, molecules, ions, or radicals, that have distinct chemical structures and properties.

Differences in chemical species can dramatically affect how substances interact with each other in chemical reactions. For instance, in the context of acid-base chemistry, a conjugate acid differs from its conjugate base by one proton.

A thorough understanding of the unique features and behaviors of various chemical species enables chemists to predict and manipulate chemical reactions effectively. This knowledge is especially important when considering the reactivity and stability of substances in both natural and synthetic processes.