Question

(a) Give the conjugate base of the following Bronsted-Lowry the following Brønsted-Lowry bases: (i) \(\mathrm{SO}_{4}^{2-}\), (ii) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) -

Short answer

The conjugate base of \(\mathrm{SO}_{4}^{2-}\) is \(\mathrm{HSO}_{4}^{-}\) and the conjugate base of \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) is \(\mathrm{CH}_{3} \mathrm{NH}_{3}^{+}\).

Step-by-step solution

(i) Conjugate base of \(\mathrm{SO}_{4}^{2-}\)

To find the conjugate base of sulfate ion (\(\mathrm{SO}_{4}^{2-}\)), we first need to add a proton (H+) to the base: \[\mathrm{SO}_{4}^{2-} + \mathrm{H}^{+} \rightarrow \mathrm{HSO}_{4}^{-}\] So, the conjugate base of \(\mathrm{SO}_{4}^{2-}\) is \(\mathrm{HSO}_{4}^{-}\).

(ii) Conjugate base of \(\mathrm{CH}_{3} \mathrm{NH}_{2}\)

To find the conjugate base of methylamine (\(\mathrm{CH}_{3} \mathrm{NH}_{2}\)), we again need to add a proton (H+) to the base: \[\mathrm{CH}_{3} \mathrm{NH}_{2} + \mathrm{H}^{+} \rightarrow \mathrm{CH}_{3} \mathrm{NH}_{3}^{+}\] So, the conjugate base of \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) is \(\mathrm{CH}_{3} \mathrm{NH}_{3}^{+}\).

Key concepts

Bronsted-Lowry Theory

The Brønsted-Lowry theory is a fundamental concept in acid-base chemistry that defines acids as proton donors and bases as proton acceptors. According to this theory, an acid-base reaction involves the transfer of a proton (H+) from the acid to the base. This proton transfer results in the formation of a conjugate base, which is what remains of the acid after it has donated the proton, and a conjugate acid, which is the base that has accepted the proton.

For example, when a substance like hydrogen chloride (HCl) donates a proton, it becomes its conjugate base, chloride ion (Cl-). Meanwhile, the receiver of that proton, often water (H2O), becomes its conjugate acid, hydronium ion (H3O+). The Brønsted-Lowry theory helps to predict the outcomes of acid-base reactions by identifying the potential conjugate acid-base pairs.

Sulfate Ion

The sulfate ion (\( \text{SO}_4^{2-} \) is a polyatomic anion composed of one sulfur atom and four oxygen atoms, carrying a net charge of -2. It is ubiquitous in nature and is part of many biological and geological processes. When discussing acid-base chemistry, the sulfate ion can act as a base.

According to the Brønsted-Lowry theory, if the sulfate ion accepts a proton, it becomes the hydrogen sulfate ion (\( \text{HSO}_4^- \)), which is its conjugate acid. This conversion indicates that the sulfate ion can participate in acid-base reactions and has the ability to form different compounds depending on the presence of protons. In solution, for instance, the balance between sulfate and hydrogen sulfate can greatly affect the pH level and chemical behavior of the system.

Methylamine

Methylamine (\( \text{CH}_3\text{NH}_2 \) is an organic compound with a simple structure where a methyl group (CH3-) is bonded to an amino group (NH2). It is a weak base in acid-base chemistry, meaning that it has a tendency to accept protons from acids. This property allows it to interact with acids forming salts.

Through the lens of the Brønsted-Lowry theory, when methylamine accepts a proton, it transforms into its conjugate acid, methylammonium (\( \text{CH}_3\text{NH}_3^+ \)). Methylamine’s ability to accept a proton and form its conjugate acid is an important characteristic in various chemical reactions, including biological pathways, industrial synthesis, and environmental processes.

Acid-Base Chemistry

Acid-base chemistry is a branch of chemical science that focuses on the properties and behavior of acids and bases. It encompasses the study of pH, pKa, equilibrium constants, buffer systems, and titration, among other topics. It's crucial for understanding many biological systems, industrial processes, and environmental phenomena.

Using the Brønsted-Lowry theory as a basis, we analyze reactions by looking at the transfer of protons between species. This understanding of proton exchange helps chemists to design reactions, predict product formation, and control experimental conditions for desired outcomes in both academic and industry settings. In the context of the classroom, acid-base chemistry is often explored through the reactions of household acids and bases, allowing students to grasp these concepts through tangible experiments.