Problem 4 - 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) \(\mathrm{HClO}_{4}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (b) \(\mathrm{NH}_{4}^{+}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (c) \(\mathrm{HCO}_{3}^{-}+\mathrm{OH}^{-} \rightarrow\)

Step-by-Step Solution

Answer

(a) Products: ClO4^- and H3O^+; (b) Products: NH3 and H3O^+; (c) Products: CO3^2- and H2O.

Step 1: Identify Reactants for Reaction (a)

The given reaction is \[\text{HClO}_{4} + \text{H}_{2}\text{O} \rightarrow \]Here, \(\text{HClO}_{4}\) is the acid and \(\text{H}_{2}\text{O}\) is the base that will accept a proton from the acid.

Step 2: Determine Products of Reaction (a)

In the reaction \[\text{HClO}_{4} + \text{H}_{2}\text{O} \rightarrow \]\(\text{HClO}_{4}\) donates a proton to \(\text{H}_{2}\text{O}\), forming \(\text{ClO}_{4}^{-}\) and \(\text{H}_{3}\text{O}^{+}\). \(\text{ClO}_{4}^{-}\) is the conjugate base of \(\text{HClO}_{4}\), and \(\text{H}_{3}\text{O}^{+}\) is the conjugate acid of \(\text{H}_{2}\text{O}\).

Step 3: Identify Reactants for Reaction (b)

The given reaction is \[\text{NH}_{4}^{+} + \text{H}_{2}\text{O} \rightarrow \]Here, \(\text{NH}_{4}^{+}\) is acting as the acid and \(\text{H}_{2}\text{O}\) is acting as the base.

Step 4: Determine Products of Reaction (b)

During the reaction \[\text{NH}_{4}^{+} + \text{H}_{2}\text{O} \rightarrow \]\(\text{NH}_{4}^{+}\) donates a proton to \(\text{H}_{2}\text{O}\), resulting in \(\text{NH}_{3}\) and \(\text{H}_{3}\text{O}^{+}\). Here, \(\text{NH}_{3}\) is the conjugate base of \(\text{NH}_{4}^{+}\), and \(\text{H}_{3}\text{O}^{+}\) is the conjugate acid of \(\text{H}_{2}\text{O}\).

Step 5: Identify Reactants for Reaction (c)

The given reaction is \[\text{HCO}_{3}^{-} + \text{OH}^{-} \rightarrow \]In this case, \(\text{HCO}_{3}^{-}\) is the acid and \(\text{OH}^{-}\) is the base.

Step 6: Determine Products of Reaction (c)

In the reaction \[\text{HCO}_{3}^{-} + \text{OH}^{-} \rightarrow \]\(\text{HCO}_{3}^{-}\) donates a proton to \(\text{OH}^{-}\), forming \(\text{CO}_{3}^{2-}\) and \(\text{H}_{2}\text{O}\). \(\text{CO}_{3}^{2-}\) is the conjugate base of \(\text{HCO}_{3}^{-}\), and \(\text{H}_{2}\text{O}\) is the conjugate acid of \(\text{OH}^{-}\).

Key Concepts

Conjugate Acid-Base Pairs

In acid-base chemistry, understanding conjugate acid-base pairs is fundamental. When an acid donates a proton (+), the product becomes a base. This product is called the conjugate base of the original acid. Similarly, when a base accepts a proton, it forms its conjugate acid. It's a simple, yet powerful, concept that explains many chemical behaviors. For instance, in the reaction \[ \text{HClO}_{4} + \text{H}_{2}\text{O} \rightarrow \text{ClO}_{4}^{-} + \text{H}_{3}\text{O}^{+} \], \( \text{HClO}_{4} \) is the acid giving up a proton and the \(\text{ClO}_{4}^{-}\) becomes its conjugate base. \(\text{H}_{2}\text{O}\) accepts a proton to form \(\text{H}_{3}\text{O}^{+}\), which is its conjugate acid. Identifying these pairs is crucial when analyzing reactions.

Proton Transfer

Proton transfer is the heart of an acid-base reaction. Essentially, it involves the movement of a proton from the acid to the base. This transfer transforms the acid into its conjugate base and the base into its conjugate acid.
Understanding this is key because it highlights the dynamic nature of chemical reactions, where protons are continually exchanged. In the reaction \[\text{NH}_{4}^{+} + \text{H}_{2}\text{O} \rightarrow \text{NH}_{3} + \text{H}_{3}\text{O}^{+} \], \(\text{NH}_{4}^{+}\) acts as an acid donating a proton to \(\text{H}_{2}\text{O}\). The outcome is \(\text{NH}_{3}\) and \(\text{H}_{3}\text{O}^{+}\), showing how proton transfer drives the chemical process.

Chemical Reactions

Every chemical reaction involves the transformation of substances through breaking and forming bonds. In acid-base reactions, these transformations focus on proton transfers. They are a subset of a broader category of reactions called exchange reactions, where substances exchange components.
These reactions are fundamental in many biological and industrial processes. For example, managing pH levels in solutions often involves acid-base reactions. An understanding of the basic mechanism, like the one involving \(\text{HCO}_{3}^{-}\) and \(\text{OH}^{-}\), is necessary for predicting outcomes and managing conditions in the lab. It illustrates how chemical reactions can be controlled by manipulating reactants.

Reaction Products Identification

Identifying reaction products is vital for understanding and predicting chemical reactions. After an acid-base reaction, recognizing the resulting products involves determining the new forms of the original acid and base. For instance, in the reaction \[\text{HCO}_{3}^{-} + \text{OH}^{-} \rightarrow \text{CO}_{3}^{2-} + \text{H}_{2}\text{O} \],\(\text{CO}_{3}^{2-}\) is identified as the conjugate base of \(\text{HCO}_{3}^{-}\) and \(\text{H}_{2}\text{O}\) as the conjugate acid of \(\text{OH}^{-}\). This helps in understanding the nature and ratio of substances formed. Correct identification allows chemists to anticipate the properties of products, a foundational skill in both industrial applications and scientific research.