Question

Which of the following must be an oxidation reduction reaction? Explain your answer, and include an example oxidation-reduction reaction for all that apply. a. A metal reacts with a nonmetal. b. A precipitation reaction. c. An acid-base reaction.

Short answer

Case A, where a metal reacts with a nonmetal, must be an oxidation-reduction reaction because the metal loses electrons (oxidation) and the nonmetal gains electrons (reduction). For example, when sodium reacts with chlorine to form sodium chloride: $2Na(s)+C{l}_2(g)\to 2NaCl(s)$ Neither Case B (precipitation reaction) nor Case C (acid-base reaction) are necessarily oxidation-reduction reactions, as they do not always involve the transfer of electrons.

Step-by-step solution

Case A: A metal reacts with a nonmetal

When a metal reacts with a nonmetal, the metal tends to lose electrons, and the nonmetal tends to gain electrons. This process is an oxidation-reduction reaction because the transfer of electrons occurs between the two species. Example of oxidation-reduction reaction for case A: The reaction between sodium (a metal) and chlorine (a nonmetal) to form sodium chloride: $2Na(s)+C{l}_2(g)\to 2NaCl(s)$ In this reaction, sodium loses an electron (oxidation) to form sodium ions, and chlorine gains an electron (reduction) to form chloride ions.

Case B: A precipitation reaction

A precipitation reaction occurs when two soluble compounds in solution react to form an insoluble product (called a precipitate). It does not necessarily involve the transfer of electrons, and thus, is not, by default, an oxidation-reduction reaction. It may or may not be an oxidation-reduction reaction depending on the compounds involved. Example of a precipitation reaction that is not an oxidation-reduction reaction: $AgN{O}_3(aq)+NaCl(aq)\to AgCl(s)+NaN{O}_3(aq)$ This reaction involves the formation of solid silver chloride (AgCl) from the reaction of silver nitrate (AgNO3) and sodium chloride (NaCl). There is no transfer of electrons in this reaction.

Case C: An acid-base reaction

An acid-base reaction involves the transfer of a proton (H+) from an acid to a base. It does not involve the transfer of electrons. Thus, it is not an oxidation-reduction reaction by necessity. However, it is important to note that a reaction can be both an acid-base and oxidation-reduction reaction if electron transfer is involved. Example of an acid-base reaction that is not an oxidation-reduction reaction: $HCl(aq)+NaOH(aq)\to NaCl(aq)+H_{2}O(l)$ In this reaction, hydrochloric acid (HCl) donates a proton to sodium hydroxide (NaOH), forming sodium chloride (NaCl) and water (H2O). There is no transfer of electrons in this reaction. #Conclusion# Based on the analysis above, we can conclude that Case A (metal reacts with a nonmetal) must be an oxidation-reduction reaction. Neither Case B (precipitation reaction) nor Case C (acid-base reaction) are necessarily oxidation-reduction reactions, though it is possible under specific conditions.

Key concepts

Metal and Nonmetal Reactions

When a metal reacts with a nonmetal, something quite interesting happens. The metal tends to lose electrons, while the nonmetal is eager to gain those electrons. This dance of electron exchange means we're dealing with an oxidation-reduction (redox) reaction.

Oxidation refers to the loss of electrons, which occurs to the metal, making it a positively charged ion. The nonmetal gains electrons, undergoing reduction, thus forming a negatively charged ion.

For example, let's consider the classic reaction of sodium (a metal) with chlorine (a nonmetal) to form table salt, sodium chloride:

• The balanced equation: $2Na(s)+C{l}_2(g)\to 2NaCl(s)$
• Sodium (Na) atoms lose electrons (oxidized) to form $N{a}^{+}$ ions.
• Chlorine (Cl) molecules gain electrons (reduced) to form $C{l}^{-}$ ions.

Through this process, sodium chloride is formed, and the electron transfer is complete, showcasing a quintessential redox reaction.

Precipitation Reactions

Precipitation reactions are fascinating chemical processes where two solutions combine to form an insoluble solid, known as a precipitate.

In these reactions, dissolved ionic compounds come together and result in a solid product that settles out of the solution. However, not every precipitation reaction involves an oxidation-reduction process.

Consider the reaction of silver nitrate with sodium chloride:

• The reaction: $AgN{O}_3(aq)+NaCl(aq)\to AgCl(s)+NaN{O}_3(aq)$
• Silver chloride (AgCl) precipitates out as a solid.

In this scenario, electron transfer does not take place, pointing out that precipitation reactions can often occur without being redox reactions. Understanding these differences helps clarify how these reactions are categorized.

Acid-Base Reactions

Acid-base reactions are all about the transfer of protons. In these reactions, acids donate protons ($H^{+}$) to bases, producing water and a salt. These reactions do not necessarily entail electron transfer, distinguishing them from oxidation-reduction reactions.

Here's a typical acid-base reaction:

• Example: $HCl(aq)+NaOH(aq)\to NaCl(aq)+H_{2}O(l)$
• Here, hydrochloric acid (HCl) donates a $H^{+}$ ion to sodium hydroxide (NaOH).
• The result is sodium chloride (NaCl) along with water (H2O).

While both acid-base and redox reactions can sometimes overlap, a pure acid-base reaction focuses on proton transfer without any electron movement. This makes them a distinct and vital area of study in chemistry.