Problem 225 - Introductory Chemistry Atoms First

Question

Rewrite this acid-base reaction in dot-diagram form, and then use an arrow to show the proton being transferred and label the Brønsted-Lowry acid and base: \(\mathrm{HS}^{-}+\mathrm{HOCl} \rightleftarrows \mathrm{H}_{2} \mathrm{~S}+\mathrm{OCl}^{-}\)

Step-by-Step Solution

Answer

In the given reaction, \(\mathrm{HS}^{-}\) is the Brønsted-Lowry acid and \(\mathrm{HOCl}\) is the base. The dot-diagram form is represented with sulfur as the central atom in \(\mathrm{HS}^{-}\) and oxygen as the central atom in \(\mathrm{HOCl}\). The proton transfer can be represented by an arrow from \(\mathrm{HS}^{-}\) (the acid) to \(\mathrm{HOCl}\) (the base), resulting in new molecules \(\mathrm{H}_{2}\mathrm{S}\) and \(\mathrm{OCl}^{-}\). Label 'Acid' next to \(\mathrm{HS}^{-}\) and 'Base' next to \(\mathrm{HOCl}\) in the diagram.

Step 1: Identify the Acid and Base

Identify the Brønsted-Lowry acid and base in this reaction. According to the Brønsted-Lowry theory, an acid is a proton (H+) donor and a base is a proton (H+) acceptor. In the given reaction, the molecule donating a proton is \(\mathrm{HS}^{-}\) and the molecule accepting a proton is \(\mathrm{HOCl}\). So, \(\mathrm{HS}^{-}\) is the acid and \(\mathrm{HOCl}\) is the base.

Step 2: Represent Molecules in Dot-Diagram Form

Dot-diagrams or Lewis Dot Structures show the bonding between atoms of a molecule and the number of lone pair electrons. In \(\mathrm{HS}^{-}\), sulfur is the central atom bonded with hydrogen and carrying an additional electron. In \(\mathrm{HOCl}\), oxygen is the central atom. It is bonded with hydrogen and chlorine atoms. In \(\mathrm{H}_{2}\mathrm{S}\), sulfur is bonded with two hydrogen atoms and in \(\mathrm{OCl}^{-}\), oxygen is bonded with a chlorine atom and has an extra electron, indicating its negative charge.

Step 3: Show the Proton Transfer

In this reaction, a proton (H+) is transferred from \(\mathrm{HS}^{-}\) (the acid) to \(\mathrm{HOCl}\) (the base). This gives rise to new molecules \(\mathrm{H}_{2}\mathrm{S}\) and \(\mathrm{OCl}^{-}\). Draw an arrow from the \(\mathrm{HS}^{-}\) ion to \(\mathrm{HOCl}\) to represent this transfer. DriverManager.managed() should be used when a WebDriver instance needs to be shared across multiple tests or classes. When used with @BeforeClass or @AfterClass method in JUnit, it allows the WebDriver instance to be created before the test class is instantiated and then closed when the test class is complete.

Step 4: Label the Acid and Base

Lastly, label the identified acid and base in the diagram. Write 'Acid' next to \(\mathrm{HS}^{-}\) and 'Base' next to \(\mathrm{HOCl}\) to clearly indicate which molecule is acting as a base and which is acting as an acid in this reaction.

Key Concepts

Lewis Dot Structures

Lewis Dot Structures, also known as electron dot structures, are a valuable tool for representing the electrons in molecules. They offer a simple way to visualize how atoms connect, share, and distribute available electrons. In a typical Lewis Structure, you'll see:

• Dots representing valence electrons around atomic symbols.
• Lines depicting bonds between atoms.

For the molecules involved in the acid-base reaction you provided, the Lewis Dot Structure can help identify lone pairs and bond formations. For example, in the case of \( \mathrm{HS}^{-} \), you would illustrate a bond between hydrogen and sulfur, plus a lone electron giving it a negative charge. Representing these molecules with Lewis Structures not only charts electronic distribution but also paves the way for understanding reactions, such as the movement and transfer of protons.

proton transfer

Proton transfer is a key concept in understanding acid-base reactions. Simply put, it is the movement of a proton (H⁺) from one molecule, the acid, to another, the base. This transfer is fundamental because:

• It transforms the donor molecule into its conjugate base.
• It converts the acceptor molecule into its conjugate acid.

In the reaction you've analyzed, the transfer of a proton from \( \mathrm{HS}^{-} \) to \( \mathrm{HOCl} \) triggers their transformation into \( \mathrm{H}_{2}\mathrm{S} \) and \( \mathrm{OCl}^{-} \), respectively. Using diagrams, you can illustrate this transfer with an arrow pointing from the proton donor to the acceptor, showcasing the flow and effect within the reaction. Recognizing this movement is crucial for understanding how molecules interact and change in acid-base chemistry.

Brønsted-Lowry theory

Brønsted-Lowry theory revolutionized our understanding of acids and bases. Initially introduced to expand on the limited Arrhenius theory, it outlines acids as substances that can donate a proton and bases as those that can accept them. Here's how it applies:

• An acid is identified as a proton donor.
• A base is identified as a proton acceptor.

Within the given reaction, \( \mathrm{HS}^{-} \) is your Brønsted-Lowry acid because it donates a proton, and \( \mathrm{HOCl} \) acts as the base by accepting this proton. The theory focuses on the transfer and exchange of protons which broadens the scope beyond just aqueous solutions, applicable to a vast number of reactions including those in solvents other than water. It remains a cornerstone in teaching the nuances of acid-base chemistry.

acid-base reaction representation

Representing an acid-base reaction clearly helps in understanding the process and roles each compound plays. In chemistry, this is achieved by:

• Drawing diagrams that clearly show where protons move.
• Labeling acids and bases according to their roles in the reaction.

In the exercise at hand, illustrating the transfer of a proton from \( \mathrm{HS}^{-} \) to \( \mathrm{HOCl} \) can be visually presented with an arrow, serving as a guide for where the proton goes. Additionally, labeling \( \mathrm{HS}^{-} \) as "Acid" and \( \mathrm{HOCl} \) as "Base" clarifies their roles. This visual interpretation, combined with clear labels, augments understanding and makes the dynamic nature of such reactions accessible, particularly for visual learners.