Problem 15 - Chemistry The Central Science In Si Units

Question

(a) Give the conjugate base of the following Brønsted Lowry acids: \((\mathbf{i}) \mathrm{H}_{2} \mathrm{PO}_{4}^{-},(\mathbf{i i}) \mathrm{HBr}\). (b) Give the conjugate acid of the following Brønsted-Lowry bases: \((\mathbf{i}) \mathrm{CN}^{-},(\mathbf{i i}) \mathrm{HSO}_{4}^{-}\).

Step-by-Step Solution

Answer

(a) \(\text{Conjugate bases: } \mathrm{HPO}_{4}^{2-}, \mathrm{Br}^{-}\); (b) \(\text{Conjugate acids: } \mathrm{HCN}, \mathrm{H}_2\mathrm{SO}_{4}\).

Step 1: Identify the Conjugate Base Definition

The conjugate base of a Brønsted-Lowry acid is formed by removing one proton (H⁺) from the acid. This will result in a species with one less positive charge.

Step 2: Find the Conjugate Base of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

Remove one \(\text{H}^+\) ion from \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\). This gives \(\mathrm{HPO}_{4}^{2-}\), which is the conjugate base.

Step 3: Find the Conjugate Base of \(\mathrm{HBr}\)

Remove one \(\text{H}^+\) ion from \(\mathrm{HBr}\). This gives \(\mathrm{Br}^{-}\), which is the conjugate base.

Step 4: Identify the Conjugate Acid Definition

The conjugate acid of a Brønsted-Lowry base is formed by adding one proton (H⁺) to the base. This addition of a proton results in a species with one more positive charge.

Step 5: Find the Conjugate Acid of \(\mathrm{CN}^{-}\)

Add one \(\text{H}^+\) ion to \(\mathrm{CN}^{-}\). This gives \(\mathrm{HCN}\), which is the conjugate acid.

Step 6: Find the Conjugate Acid of \(\mathrm{HSO}_{4}^{-}\)

Add one \(\text{H}^+\) ion to \(\mathrm{HSO}_{4}^{-}\). This gives \(\mathrm{H}_2\mathrm{SO}_{4}\), which is the conjugate acid.

Key Concepts

Brønsted-Lowry acids

Brønsted-Lowry acids are substances that can donate a proton, represented as \( ext{H}^+\), to another compound. In simpler terms, they actively give away a proton to facilitate a chemical reaction. This act of donating protons makes them central players in proton transfer reactions.
In the context of conjugate acid-base pairs, a Brønsted-Lowry acid, after losing a proton, turns into a conjugate base. For instance, when \( \mathrm{H}_2 \mathrm{PO}_4^- \) donates a proton, it transforms into \( \mathrm{HPO}_4^{2-} \), its conjugate base. Here, \( \mathrm{HBr} \) changes to \( \mathrm{Br}^- \) upon losing a proton. Such transformations highlight the dynamic nature of acids in chemical reactions.
Key properties of Brønsted-Lowry acids include:

• Act as proton donors
• Form conjugate bases upon donating a proton
• Play pivotal roles in acid-base reactions

Brønsted-Lowry bases

Brønsted-Lowry bases are substances that can accept a proton from another compound. When they gain this proton, they transform into their conjugate acids. This transformation demonstrates their role as proton acceptors in chemical reactions. For example, when \( \mathrm{CN}^- \) accepts a proton, it becomes \( \mathrm{HCN} \), its conjugate acid. Similarly, \( \mathrm{HSO}_4^- \) becomes \( \mathrm{H}_2\mathrm{SO}_4 \) after gaining a proton.
Here are a few characteristics of Brønsted-Lowry bases:

• Serve as proton acceptors
• Form conjugate acids upon accepting a proton
• Essential components in neutralizing acids in reactions

By understanding these properties, you can better appreciate how bases interact with acids during proton transfer processes.

proton transfer reactions

Proton transfer reactions are a fundamental type of chemical reaction involving the transfer of protons between a donor and an acceptor. In this context, the donor is the Brønsted-Lowry acid, while the acceptor is the Brønsted-Lowry base. The transferred proton changes one substance into its conjugate base and the other into its conjugate acid.
These reactions are crucial in many biological and chemical processes. For example, during digestion, stomach acids donate protons to substances in food, aiding in their breakdown. In laboratory settings, these reactions are central to titrations, where acids and bases neutralize each other.
Key concepts to remember about proton transfer reactions include:

• Involve the transfer of protons between acids and bases
• Result in the formation of conjugate acid-base pairs
• Influence the pH and reactivity of solutions

Understanding proton transfer reactions allows us to predict the outcomes of acid-base interactions in various contexts.