Problem 29 - General Chemistry: Principles and Modern Applications

Question

In this chapter, we described an acid as a substance capable of producing \(\mathrm{H}^{+}\) and a salt as the ionic compound formed by the neutralization of an acid by a base. Write ionic equations to show that sodium hydrogen sulfate has the characteristics of both a salt and an acid (sometimes called an acid salt).

Step-by-Step Solution

Answer

Sodium hydrogen sulfate \(\mathrm{NaHSO}_4\) can behave as both an acid and a salt. As an acid, it splits into \(\mathrm{H}^{+}\) and \(\mathrm{SO}_4^{2-}\) when in an aqueous solution: \(\mathrm{HSO}_4^{-} (aq) \rightarrow \mathrm{H}^{+} (aq) + \mathrm{SO}_4^{2-} (aq)\). As a salt, it can be formed through the neutralization of sulfuric acid (\(H_2SO_4\)) by sodium hydroxide (\(NaOH\)), as shown by: \(H_2SO_4 (aq) + 2NaOH (aq) \rightarrow 2H_2O (l) + NaHSO_4 (aq)\).

Step 1: Understanding the Molecular Structure

The molecular formula for sodium hydrogen sulfate is \(NaHSO_4\). It is made up of a sodium ion \(\mathrm{Na}^{+}\) and a hydrogen sulfate ion \(\mathrm{HSO}_4^{-}\).

Step 2: Behavior as an Acid

As an acid, it should be capable of producing \(\mathrm{H}^{+}\) when dissolved in water. The ionic equation reflecting this is: \(\mathrm{HSO}_4^{-} (aq) \rightarrow \mathrm{H}^{+} (aq) + \mathrm{SO}_4^{2-} (aq)\). This equation shows that when hydrogen sulfate ion is in an aqueous solution, it splits into \(\mathrm{H}^{+}\) and \(\mathrm{SO}_4^{2-}\). This justifies it as an acid.

Step 3: Behavior as a Salt

A salt is formed by the neutralization of an acid by a base. This can be demonstrated by showing the reaction of sulfuric acid (\(H_2SO_4\)) and sodium hydroxide (\(NaOH\)), a base. The ionic equation would be: \(H_2SO_4 (aq) + 2NaOH (aq) \rightarrow 2H_2O (l) + Na_2SO_4 (aq)\). If you remove one hydrogen from the reactant side, you end up with sodium hydrogen sulfate (\(NaHSO_4\)) instead of sodium sulfate (\(Na_2SO_4\)), showing it can be derived from a neutralization reaction.

Key Concepts

Ionic Equations

Ionic equations are a crucial tool in chemistry used to show the details of chemical reactions, especially those happening in aqueous solutions. In these equations, substances are usually presented in their ionic forms because many compounds dissociate into ions in water. This can help illustrate what happens at the molecular level, particularly in reactions involving acids and bases.
For example, when sodium hydrogen sulfate (\(NaHSO_4\)) is dissolved in water, it acts as an acid by dissociating into \(\mathrm{H}^{+}\), \(\mathrm{Na}^{+}\), and \(\mathrm{SO}_4^{2-}\) ions. This dissociation is represented by the ionic equation:

• \(\mathrm{HSO}_4^{-} (aq) \rightarrow \mathrm{H}^{+} (aq) + \mathrm{SO}_4^{2-} (aq)\)

Understanding these reactions at the ionic level allows students to see how molecules interact in solutions and changes that occur during chemical reactions.

Acid Salts

An acid salt is a type of salt that forms when a partially neutralized multivalent acid contains replaceable hydrogen atoms. Unlike typical salts, which fully neutralize an acid, acid salts retain some acidity and have hydrogen ions available for donation.
In the case of sodium hydrogen sulfate (\(NaHSO_4\)), it behaves as an acid salt because it can release a \(\mathrm{H}^{+}\) ion in water. It stems from a partial reaction of sulfuric acid \((H_2SO_4)\) with a base like sodium hydroxide \((NaOH)\). This partial reaction makes \(NaHSO_4\) both a salt and an acid due to its chemical composition.
Therefore, sodium hydrogen sulfate can act in two roles:

• As an acid, donating hydrogen ions.
• As a salt, having emerged from a neutralization process that was not fully complete.

These characteristics highlight the dual property of acid salts to serve various chemical functions.

Neutralization Reaction

Neutralization reactions are foundational to understanding how acids and bases interact. These reactions occur when an acid and a base combine to produce a salt and water. In its simplest form, it can be written as an equation:
\[ \mathrm{Acid} + \mathrm{Base} \rightarrow \mathrm{Salt} + \mathrm{Water} \]
This type of reaction perfectly illustrates the creation of sodium hydrogen sulfate, an acid salt. When sulfuric acid \((H_2SO_4)\), a strong acid, reacts with sodium hydroxide \((NaOH)\), a strong base, a typical neutralization reaction takes place. If the reaction is stopped before full completion, it results in sodium hydrogen sulfate:

• \(H_2SO_4 (aq) + NaOH (aq) \rightarrow H_2O (l) + NaHSO_4 (aq)\)

This showcases that even incomplete neutralization can lead to the formation of acid salts, like \(NaHSO_4\). The sodium hydrogen sulfate retains the potential to behave as an acid, further exemplifying the fascinating dynamics in acid-base chemistry.