Question

Write the formula for the conjugate base of each acid. (a) \(\mathrm{HCl}\) (b) \(\mathrm{H}_{2} \mathrm{SO}_{3}\) (c) \(\mathrm{HCHO}_{2}\) (d) HF

Short answer

The conjugate bases are (a) Cl-, (b) HSO3-, (c) CHO2-, and (d) F-.

Step-by-step solution

Definition of Conjugate Base

A conjugate base is formed by the removal of a proton (H+) from an acid. Remember that the conjugate base of an acid will always have one less hydrogen atom and will possess a negative charge as compared to the original acid molecule.

Identify Conjugate Base of HCl

Remove a proton from hydrochloric acid (HCl) to get its conjugate base. HCl loses an H+ ion to form Cl-, which is the conjugate base of HCl.

Identify Conjugate Base of H2SO3

Remove a proton from sulfurous acid (H2SO3) to get its conjugate base. H2SO3 loses an H+ ion to form HSO3-, which is the conjugate base of H2SO3.

Identify Conjugate Base of HCHO2

Remove a proton from formic acid (HCHO2) to get its conjugate base. HCHO2 loses an H+ ion to form CHO2-, which is the conjugate base of HCHO2.

Identify Conjugate Base of HF

Remove a proton from hydrofluoric acid (HF) to get its conjugate base. HF loses an H+ ion to form F-, which is the conjugate base of HF.

Key concepts

Acid-Base Chemistry

Acid-base chemistry is a foundational concept within the field of chemistry, focusing on the properties and behaviors of acids and bases. At its core, it's about the exchange of protons (H⁺) between substances. When we talk about acids, we often refer to substances that can donate a proton, while bases are those that can accept a proton.

This exchange is essential for many chemical reactions and biological processes. In the context of conjugate bases, it's crucial to understand that when an acid donates its proton, what remains is called its 'conjugate base'. This conjugate base is integral in reacting further to potentially form its conjugate acid by accepting a proton. For example, after hydrochloric acid (HCl) donates a proton, the chloride ion (Cl^-) becomes its conjugate base; it's ready to accept a proton if available.

Proton Transfer Reactions

Proton transfer reactions are the core of many chemical processes, especially in acid-base chemistry. These reactions are characterized by one substance (the acid) passing a proton to another substance (the base). The ability to transfer a proton is a fundamental property that defines acids and bases within the Brønsted-Lowry framework.

Understanding this concept helps clarify how conjugate bases are formed. The reaction of an acid like sulfurous acid (H₂SO₃) with a base involves the transfer of a proton from the acid to the base, resulting in the formation of the conjugate base (HSO₃^-). These reactions can be reversible, with the newly formed bases capable of accepting the proton back, thus behaving as Brønsted-Lowry bases.

Brønsted-Lowry Acids and Bases

According to the Brønsted-Lowry theory, an acid is any substance that can donate a proton, whereas a base is any substance that can accept a proton. This approach extends the category of acids and bases beyond those that simply generate hydrogen or hydroxide ions in water.

For example, hydrogen fluoride (HF) is a Brønsted-Lowry acid because it has the potential to donate a proton to form its conjugate base, fluoride (F^-). Similarly, after the proton is donated, the remaining molecule is capable of accepting a proton, qualifying it as a Brønsted-Lowry base. This acid-base pair, HF and F^-, is tightly linked by their ability to transform into each other through the gain or loss of a proton.