Question

Identify the Bronsted-Lowry acid and base in each of the following neutralization reactions: (a) \(\mathrm{HI}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{I}^{-}(a q)\) (b) \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\mathrm{HS}^{-}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{~S}(a q)+\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}(a q)\)

Short answer

(a) Acid: HI, Base: H2O. (b) Acid: HC2H3O2, Base: HS-.

Step-by-step solution

Identify the Acid and Base in Reaction (a)

In the reaction \(\mathrm{HI}(a q) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{3} \mathrm{O}^{+}(a q) + \mathrm{I}^{-}(a q)\), identify which species donates a proton (\(\text{H}^+\)) and which one accepts it.\ \ - \(\mathrm{HI}\) donates a proton to form \(\mathrm{I}^{-}\), acting as the Bronsted-Lowry acid.\ \ - \(\mathrm{H}_{2} \mathrm{O}\) accepts the proton to become \(\mathrm{H}_{3} \mathrm{O}^{+}\), acting as the Bronsted-Lowry base.

Identify the Acid and Base in Reaction (b)

In the reaction \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q) + \mathrm{HS}^{-}(a q) \rightarrow \mathrm{H}_{2} \mathrm{S}(a q) + \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}(a q)\), identify the proton donor and acceptor: \ \ - \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) donates a proton and converts into \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\), acting as the Bronsted-Lowry acid.\ \ - \(\mathrm{HS}^{-}\) accepts the proton and forms \(\mathrm{H}_{2} \mathrm{S}\), acting as the Bronsted-Lowry base.

Key concepts

Acid-Base Reactions

In chemistry, an acid-base reaction is a process where an acid and a base interact to form new chemical substances. This type of reaction is fundamental in understanding the behavior of acids and bases in various chemical contexts. According to the Bronsted-Lowry theory, acids are species that donate protons (H⁺ ions), while bases are those that accept protons.

To visualize this, consider the reaction between hydriodic acid (HI) and water (H₂O). In this reaction,

• HI donates a proton to water, which is why HI is the acid.
• Water accepts this proton to form hydronium ions (H₃O⁺), hence acting as the Bronsted-Lowry base.

Understanding acid-base reactions involves recognizing these roles. Identifying which molecules donate or accept protons is key in naming the substances in the reaction as acids or bases.

Neutralization Reactions

Neutralization reactions occur when an acid reacts with a base to produce water and a salt. This type of reaction typically leads to the 'neutralization' of the acid and base properties, resulting in products that are neither strongly acidic nor basic. It is a critical concept in chemistry for applications like titrations, where the concentration of a solution is determined by reacting it with a solution of known concentration.

Take, for instance, the example of the acetic acid (HC₂H₃O₂) reacting with the hydrogen sulfide ion (HS⁻). Here:

• Acetic acid donates a proton to HS⁻, resulting in the formation of hydrosulfuric acid (H₂S).
• This exchange leads to the formation of acetate ions (C₂H₃O₂⁻) along with H₂S, which are unlike the strong acid and base we started with, thus neutralizing each other's effects.

Neutralization is an essential part of managing pH in various solutions and everyday products.

Proton Transfer Reactions

Proton transfer reactions are central to the Bronsted-Lowry theory. They involve the movement of protons (H⁺ ions) from one substance to another, dictating the role of acids and bases in a chemical reaction. The key feature of these reactions is the exchange of protons between reactants. Looking at a specific example, in the reaction

• Between HI and H₂O, the proton (H⁺) is transferred from HI to H₂O. This transfer creates hydronium ions (H₃O⁺) and iodide ions (I⁻).
• Similarly, in the other reaction, the proton is transferred from HC₂H₃O₂ to HS⁻, leading to the formation of H₂S and acetate ions.

Understanding proton transfer is essential in mastering concepts of acidity and basicity, as it directly influences chemical behavior. The Bronsted-Lowry acid-base model emphasizes this transfer, making it more versatile than other acid-base theories.