Problem 3 - Chemistry and Chemical Reactivity

Question

What are the products of each of the following acid-base reactions? Indicate the acid and its conjugate base and the base and its conjugate acid. (a) \(\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (b) \(\mathrm{HSO}_{4}^{-}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (c) \(\mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{F}^{-} \rightarrow\)

Step-by-Step Solution

Answer

(a) \( \mathrm{NO}_3^- + \mathrm{H}_3O^+ \). (b) \( \mathrm{SO}_4^{2-} + \mathrm{H}_3O^+ \). (c) \( \mathrm{H}_2O + \mathrm{HF} \).

Step 1: Identify Reactants in (a)

In the reaction \( \mathrm{HNO}_3 + \mathrm{H}_2O \rightarrow \), \( \mathrm{HNO}_3 \) is the acid because it donates a proton (\( \mathrm{H}^+ \)), and \( \mathrm{H}_2O \) is the base since it accepts a proton.

Step 2: Write Products for (a)

When \( \mathrm{HNO}_3 \) donates a proton to \( \mathrm{H}_2O \), it forms the conjugate base \( \mathrm{NO}_3^- \). The \( \mathrm{H}_2O \), having gained a proton, forms the conjugate acid \( \mathrm{H}_3O^+ \). Thus, the products are \( \mathrm{NO}_3^- + \mathrm{H}_3O^+ \).

Step 3: Identify Reactants in (b)

In \( \mathrm{HSO}_4^- + \mathrm{H}_2O \rightarrow \), \( \mathrm{HSO}_4^- \) is the acid, donating a proton, while \( \mathrm{H}_2O \) acts as the base, accepting the proton.

Step 4: Write Products for (b)

When \( \mathrm{HSO}_4^- \) donates a proton to \( \mathrm{H}_2O \), it forms \( \mathrm{SO}_4^{2-} \) (conjugate base). \( \mathrm{H}_2O \) becomes \( \mathrm{H}_3O^+ \) (conjugate acid). So, the products are \( \mathrm{SO}_4^{2-} + \mathrm{H}_3O^+ \).

Step 5: Identify Reactants in (c)

In \( \mathrm{H}_3O^+ + \mathrm{F}^- \rightarrow \), \( \mathrm{H}_3O^+ \) acts as the acid, donating a proton. \( \mathrm{F}^- \) is the base as it accepts the proton.

Step 6: Write Products for (c)

When \( \mathrm{H}_3O^+ \) donates a proton to \( \mathrm{F}^- \), it forms \( \mathrm{H}_2O \) (conjugate base). \( \mathrm{F}^- \), when it gains a proton, becomes \( \mathrm{HF} \) (conjugate acid). Therefore, the products are \( \mathrm{H}_2O + \mathrm{HF} \).

Key Concepts

Conjugate Acid-Base Pairs

In acid-base reactions, reacting species are acids and bases, which transform into their respective conjugates. Here, the acid is the proton donor, and the base is the proton acceptor. Conjugate pairs are directly linked by this proton exchange. This concept is essential to understand the relationship between acids and their conjugate bases, as well as bases and their conjugate acids.

Consider the reaction of nitric acid (\( \mathrm{HNO}_3 \)) with water \( (\mathrm{H}_2O) \). \( \mathrm{HNO}_3 \) donates a proton to \( \mathrm{H}_2O \), creating \( \mathrm{NO}_3^- \) and \( \mathrm{H}_3O^+ \):

• \( \mathrm{HNO}_3 \) (acid) transforms into \( \mathrm{NO}_3^- \) (conjugate base)
• \( \mathrm{H}_2O \) (base) transforms into \( \mathrm{H}_3O^+ \) (conjugate acid)

Similar conjugate relationships are found in other reactions:- \( \mathrm{HSO}_4^- \) with water yields \( \mathrm{SO}_4^{2-} \) and \( \mathrm{H}_3O^+ \)- \( \mathrm{H}_3O^+ \) with \( \mathrm{F}^- \) yields \( \mathrm{H}_2O \) and \( \mathrm{HF} \). Understanding these pairs assists in predicting the outcome of acid-base reactions.

Proton Transfer

Proton transfer is the heart of any acid-base reaction. It involves the movement of protons (\( \mathrm{H}^+ \)) from an acid to a base. This exchange alters the identity of the substances involved, creating new compounds as products.

Imagine the transfer between sulfurous acid ion \( (\mathrm{HSO}_4^-) \) and water. When \( \mathrm{HSO}_4^- \) donates its proton, it becomes \( \mathrm{SO}_4^{2-} \), while \( \mathrm{H}_2O \) acquires the proton, forming \( \mathrm{H}_3O^+ \). This kind of transfer shows how acids and bases modify each other:- Acids donate protons to become conjugate bases.- Bases accept protons to become conjugate acids.
These transfers are not confined to laboratory settings but occur in natural and industrial processes alike, influencing various chemical balances in ecosystems and human metabolism.

Reaction Products

The culmination of proton transfers in acid-base reactions leads to the formation of distinct reaction products. These products are characterized by their conjugate acid-base nature, representing the chemical shift that occurs in the exchange.

In the reaction of hydronium ion \((\mathrm{H}_3O^+)\) with fluoride \((\mathrm{F}^-)\), the products are water \((\mathrm{H}_2O)\) and hydrogen fluoride \((\mathrm{HF})\):

• \( \mathrm{H}_3O^+ \) gives up a proton to form \( \mathrm{H}_2O \) (conjugate base)
• \( \mathrm{F}^- \) accepts the proton to become \( \mathrm{HF} \) (conjugate acid)

Such transformations are integral for the synthesis of various compounds. They ensure the availability of substances in desirable forms and concentrations, which are crucial in chemical industry and environmental chemistry.
Understanding reaction products helps in anticipating the impact of specific reactions, crucial for controlling chemical processes.