Question

Write the conjugate base for each of the following. a. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) b. \(\mathrm{HCO}_{3}^{-}\) c. HF d. \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Short answer

The conjugate bases for the given acids are: a. \( \mathrm{H}_{2} \mathrm{PO}_{4}^{-} \) b. \( \mathrm{CO}_{3}^{2-} \) c. F- d. \( \mathrm{HSO}_{4}^{-} \)

Step-by-step solution

Find the conjugate base for H3PO4

To find the conjugate base, we will remove one proton (H+) from the acid. \( \mathrm{H}_{3} \mathrm{PO}_{4} \) will lose a proton to form \( \mathrm{H}_{2} \mathrm{PO}_{4}^{-} \) as the conjugate base.

Find the conjugate base for HCO3-

To find the conjugate base, we will remove one proton (H+) from the acid. \( \mathrm{HCO}_{3}^{-} \) will lose a proton to form \( \mathrm{CO}_{3}^{2-} \) as the conjugate base.

Find the conjugate base for HF

To find the conjugate base, we will remove one proton (H+) from the acid. HF will lose a proton to form F- as the conjugate base.

Find the conjugate base for H2SO4

To find the conjugate base, we will remove one proton (H+) from the acid. \( \mathrm{H}_{2} \mathrm{SO}_{4} \) will lose a proton to form \( \mathrm{HSO}_{4}^{-} \) as the conjugate base.

Key concepts

Acid-Base Chemistry

Acid-base chemistry revolves around the substances that donate and accept protons, categorized as acids and bases, respectively. This area is fundamental to understanding reactions in chemistry, as it dictates how different substances interact and change during a reaction.

For instance, in the textbook problem where students are required to identify the conjugate base, they are essentially looking at the other half of an acid-base reaction. The creation of a conjugate base occurs when an acid donates a proton (H+), fundamentally altering its chemical structure. This not only explains what species are present after a reaction, but also gives insight into the strength of acids and bases, with strong acids producing weaker conjugate bases, and vice versa.

Brønsted-Lowry Theory

The Brønsted-Lowry theory provides a more specific way to view acid-base reactions, focusing on the transfer of protons. According to this theory, an acid is defined as a proton donor and a base as a proton acceptor.

In our exercise example, the compounds like \( \mathrm{H}_{3}\mathrm{PO}_{4} \), \( \mathrm{HCO}_{3}^{-} \), HF, and \( \mathrm{H}_{2} \mathrm{SO}_{4} \) are recognized as acids because they each donate a proton. After the donation, the remaining species is called the 'conjugate base' of the initial acid. The Brønsted-Lowry theory thus helps students visualize the transformation that acids undergo during chemical reactions, highlighting the reversible nature of these reactions.

Chemical Equilibrium

Chemical equilibrium is the state in which the concentrations of all reactants and products remain constant over time, as the forward and reverse reactions occur at equal rates. This is a crucial concept when dealing with acid-base reactions, especially when considering the dissociation of weak acids or bases in solution.

When writing the conjugate base for acids in the exercise, we can imply that, in a reversible acid-base reaction, the acid will continuously cycle between donating and accepting protons with its conjugate base being formed and reformed in equilibrium. Understanding this dynamic balance aids students in grasping the subtle nuances of reaction directionality and the system's response to changes, in accordance with Le Chatelier's principle.

Proton Transfer Reactions

Proton transfer reactions are at the heart of acid-base chemistry. They involve the movement of protons from one molecule (the acid) to another (the base). The simplicity of the concept belies its complexity; the rate, direction, and products of proton transfer reactions depend on various factors including the nature of the acid and base, their concentrations, and the solvent.

In the exercise, understanding proton transfer reactions is key to identifying the conjugate base. When a substance like \( \mathrm{HCO}_{3}^{-} \) loses a proton, it undergoes a transformation into \( \mathrm{CO}_{3}^{2-} \), showcasing a fundamental proton transfer. This interaction allows students to better comprehend how molecules change during chemical reactions and lays the groundwork for exploring reaction mechanisms.