Question

Identify each of the following reactions as being a neutralization, precipitation, or oxidation-reduction reaction. (a) $$ \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{CO}(g) \longrightarrow 2 \mathrm{Fe}(s)+3 \mathrm{CO}_{2}(g) $$ (b) $$ \mathrm{Na}_{2} \mathrm{SO}_{4}(a q)+\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(a q) \stackrel{\longrightarrow}{\mathrm{HgSO}_{4}(s)+2 \mathrm{NaNO}_{3}(a q)} $$ (c) $$ \mathrm{CsOH}(a q)+\mathrm{HClO}_{4}(a q) \stackrel{\longrightarrow}{\mathrm{Cs}^{+}(a g)}+2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{ClO}_{4}^{-}(a a) $$ (d) $$ \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(g)+\mathrm{Na}_{2} \mathrm{~S}(a q) \longrightarrow \mathrm{MgS}(s)+2 \mathrm{NaNO}_{3}(a q) $$

Short answer

(a) Oxidation-reduction, (b) Precipitation, (c) Neutralization, (d) Precipitation.

Step-by-step solution

Identify Reaction (a)

Review the reaction: \( \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{CO}(g) \longrightarrow 2 \mathrm{Fe}(s)+3 \mathrm{CO}_{2}(g) \). Notice that iron oxide \( (\mathrm{Fe}_2\mathrm{O}_3) \) is reduced to iron \( (\mathrm{Fe}) \), and carbon monoxide \( (\mathrm{CO}) \) is oxidized to carbon dioxide \( (\mathrm{CO}_2) \). So, this is an oxidation-reduction reaction.

Identify Reaction (b)

Examine the reaction: \( \mathrm{Na}_{2} \mathrm{SO}_{4}(aq) + \mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(aq) \longrightarrow \mathrm{HgSO}_{4}(s) + 2 \mathrm{NaNO}_{3}(aq) \). Here, a solid \( \mathrm{HgSO}_{4} \) is formed from two aqueous solutions, indicating formation of a precipitate. Hence, this reaction is a precipitation reaction.

Identify Reaction (c)

Look at the reaction: \( \mathrm{CsOH}(aq) + \mathrm{HClO}_{4}(aq) \longrightarrow \mathrm{Cs}^{+}(aq) + 2 \mathrm{H}_{2}\mathrm{O}(l) + \mathrm{ClO}_{4}^{-}(aq) \). The reaction involves an acid and a base forming water, characteristic of a neutralization reaction.

Identify Reaction (d)

Review the reaction: \( \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(g) + \mathrm{Na}_{2} \mathrm{~S}(aq) \longrightarrow \mathrm{MgS}(s) + 2 \mathrm{NaNO}_{3}(aq) \). A solid \( \mathrm{MgS} \) forms from aqueous solutions, indicating this is a precipitation reaction.

Key concepts

Oxidation-Reduction Reactions

An oxidation-reduction reaction, also known as a redox reaction, involves the transfer of electrons between substances. These reactions are a significant component of chemistry as they include the processes of rusting, combustion, and even cellular respiration.
One substance gains electrons (reduction), while the other loses electrons (oxidation). For instance, in the reaction \( \mathrm{Fe}_{2} \mathrm{O}_{3}(s) + 3 \mathrm{CO}(g) \longrightarrow 2 \mathrm{Fe}(s) + 3 \mathrm{CO}_{2}(g) \), iron oxide \( (\mathrm{Fe}_2\mathrm{O}_3) \) reduces to iron \( (\mathrm{Fe}) \), gaining electrons. Meanwhile, carbon monoxide \( (\mathrm{CO}) \) oxidizes to carbon dioxide \( (\mathrm{CO}_2) \), losing electrons.
Key indications of redox reactions include a change in oxidation states of the elements involved. Remember, oxidation and reduction always go hand-in-hand - one can't occur without the other in a redox process.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions combine to form an insoluble solid, known as a precipitate. These reactions are essential in analytical chemistry for the purpose of determining the composition of a solution.
During this type of reaction, the ions in the solution pair up in such a way that an insoluble compound is created. Using the example \( \mathrm{Na}_{2} \mathrm{SO}_{4}(aq) + \mathrm{Hg} \left(\mathrm{NO}_{3}\right)_{2}(aq) \longrightarrow \mathrm{HgSO}_{4}(s) + 2 \mathrm{NaNO}_{3}(aq) \), mercury sulfate \( (\mathrm{HgSO}_{4}) \) forms as a solid from aqueous sodium sulfate and mercuric nitrate solutions.
To predict a precipitation reaction, consult the solubility rules, which help determine whether a solid will form. Precipitation reactions are not just limited to chemistry labs; they are also critical in water treatment processes to remove contaminants.

Neutralization Reactions

Neutralization reactions are a subtype of double replacement reactions where an acid reacts with a base to form water and an ionic compound, typically a salt. This reaction is fundamental for areas such as biochemistry and environment science, as it related to pH balance and buffer solutions.
In the reaction \( \mathrm{CsOH}(aq) + \mathrm{HClO}_{4}(aq) \longrightarrow \mathrm{Cs}^{+}(aq) + 2 \mathrm{H}_{2} \mathrm{O}(l) + \mathrm{ClO}_{4}^{-}(aq) \), cesium hydroxide (a base) reacts with perchloric acid to produce water, a classic hallmark of neutralization.
Neutralization reactions are remarkably vital in various industrial and everyday processes, such as antacid consumption to relieve indigestion and the formulation of soaps. In understanding these reactions, one appreciates the importance of balancing pH levels and how various substances can react to modify acidity or alkalinity in solutions.