Question

Identify each of the following unbalanced reaction equations as belonging to one or more of the following categories: precipitation, acid-base, or oxidation-reduction. a. \(\mathrm{K}_{2} \mathrm{SO}_{4}(a q)+\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q) \rightarrow \mathrm{BaSO}_{4}(s)+\mathrm{KNO}_{3}(a q)\) b. \(\mathrm{HCl}(a q)+\mathrm{Zn}(s) \rightarrow \mathrm{H}_{2}(g)+\mathrm{ZnCl}_{2}(a q)\) c. \(\mathrm{HCl}(a q)+\mathrm{AgNO}_{3}(a q) \rightarrow \mathrm{HNO}_{3}(a q)+\mathrm{AgCl}(s)\) d. \(\mathrm{HCl}(a q)+\mathrm{KOH}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{KCl}(a q)\) e. \(\mathrm{Zn}(s)+\mathrm{CuSO}_{4}(a q) \rightarrow \mathrm{ZnSO}_{4}(a q)+\mathrm{Cu}(s)\) f. \(\mathrm{NaH}_{2} \mathrm{PO}_{4}(a q)+\mathrm{NaOH}(a q) \rightarrow \mathrm{Na}_{3} \mathrm{PO}_{4}(a q)+\) \(\mathrm{H}_{2} \mathrm{O}(l)\) \(\mathrm{g} \cdot \mathrm{Ca}(\mathrm{OH})_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{O}(l)\) h. \(\mathrm{ZnCl}_{2}(a q)+\mathrm{Mg}(s) \rightarrow \mathrm{Zn}(s)+\mathrm{MgCl}_{2}(a q)\) i. \(\mathrm{BaCl}_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{BaSO}_{4}(s)+\mathrm{HCl}(a q)\)

Short answer

a. Precipitation reaction b. Oxidation-reduction (redox) reaction c. Precipitation and redox reaction d. Acid-base reaction e. Oxidation-reduction (redox) reaction f. Acid-base reaction g. Precipitation and acid-base reaction h. Oxidation-reduction (redox) reaction i. Precipitation and redox reaction

Step-by-step solution

Identify the reaction type

This reaction involves the formation of an insoluble solid, so it is a precipitation reaction. b. \(\mathrm{HCl}(a q)+\mathrm{Zn}(s) \rightarrow \mathrm{H}_{2}(g)+\mathrm{ZnCl}_{2}(a q)\)

Identify the reaction type

This reaction involves the transfer of electrons from Zn to HCl, resulting in a change in oxidation states. This is an oxidation-reduction (redox) reaction. c. \(\mathrm{HCl}(a q)+\mathrm{AgNO}_{3}(a q) \rightarrow \mathrm{HNO}_{3}(a q)+\mathrm{AgCl}(s)\)

Identify the reaction type

This reaction involves the formation of an insoluble solid and transfer of electrons between species. It is both a precipitation and a redox reaction. d. \(\mathrm{HCl}(a q)+\mathrm{KOH}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{KCl}(a q)\)

Identify the reaction type

This reaction involves the transfer of a proton (H⁺) from HCl to KOH to form water. It is an acid-base reaction. e. \(\mathrm{Zn}(s)+\mathrm{CuSO}_{4}(a q) \rightarrow \mathrm{ZnSO}_{4}(a q)+\mathrm{Cu}(s)\)

Identify the reaction type

This reaction involves the transfer of electrons from Zn to Cu, resulting in a change in oxidation states. It is an oxidation-reduction (redox) reaction. f. \(\mathrm{NaH}_{2} \mathrm{PO}_{4}(a q)+\mathrm{NaOH}(a q) \rightarrow \mathrm{Na}_{3} \mathrm{PO}_{4}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\)

Identify the reaction type

This reaction involves the transfer of a proton (H⁺) from NaH2PO4 to NaOH to form water. It is an acid-base reaction. g. \(\mathrm{Ca}(\mathrm{OH})_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{O}(l)\)

Identify the reaction type

This reaction involves both the formation of an insoluble solid and the transfer of a proton (H⁺) to form water. It is both a precipitation and an acid-base reaction. h. \(\mathrm{ZnCl}_{2}(a q)+\mathrm{Mg}(s) \rightarrow \mathrm{Zn}(s)+\mathrm{MgCl}_{2}(a q)\)

Identify the reaction type

This reaction involves the transfer of electrons from Mg to ZnCl₂, resulting in a change in oxidation states. It is an oxidation-reduction (redox) reaction. i. \(\mathrm{BaCl}_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{BaSO}_{4}(s)+\mathrm{HCl}(a q)\)

Identify the reaction type

This reaction involves both the formation of an insoluble solid and the transfer of electrons between species. It is both a precipitation and a redox reaction.

Key concepts

Precipitation Reactions

In chemistry, precipitation reactions occur when two soluble substances in a solution react to form an insoluble substance—called a precipitate—that separates from the solution. This means the products of the reaction include a solid that falls out of the liquid mixture, akin to snowflakes forming in a snow globe. These reactions are most often encountered in ionic compounds, such as salts, where ions exchange partners among the compounds.

• Example: In the reaction \(\mathrm{Ca(OH)_2}(aq) + \mathrm{H_2SO_4}(aq) \rightarrow \mathrm{CaSO_4}(s) + \mathrm{H_2O}(l)\), calcium sulfate (\(\mathrm{CaSO_4}\)) precipitates out of the solution.


• Significance: Precipitation reactions are used in various applications like qualitative inorganic analysis to identify the presence of specific ions in a solution.

It's important to differentiate between the spectator ions, which do not participate in the reaction, and the ions that form the precipitate; focusing on these helps identify whether a reaction results in precipitation. Understanding solubility rules is fundamental in predicting whether a precipitate will form. A rule of thumb is that nitrates and most alkali metal compounds are soluble, while sulfates and halides vary based on cation involved.

Acid-Base Reactions

Acid-base reactions are common and vital in chemistry, involving the transfer of protons (\(\mathrm{H^+}\) ions) from one reactant, the acid, to another, the base. This process results typically in the formation of water and a salt. Think of it as a chemical balancing act where acids and bases react to neutralize each other.

• Example: In the reaction \(\mathrm{HCl}(aq) + \mathrm{KOH}(aq) \rightarrow \mathrm{H_2O}(l) + \mathrm{KCl}(aq)\), hydrochloric acid (\(\mathrm{HCl}\)) donates a proton to potassium hydroxide (\(\mathrm{KOH}\)), forming water and potassium chloride.


• Application: These reactions are crucial in titrations, a technique used to determine the concentration of an unknown acid or base solution.

Many acid-base reactions follow the Brønsted-Lowry acid-base theory, where acids donate protons, and bases accept them. This transfer is not just confined to liquid solutions but can occur in gas and solid states as well. An understanding of pH, a measure of the hydrogen ion concentration, is vital for working with acid-base reactions. The pH scale ranges from 0 to 14, where 7 is neutral, values less than 7 are acidic, and values greater than 7 are basic.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, or redox reactions, are chemical processes where electrons are transferred between substances. Key to these reactions are the concepts of oxidation—loss of electrons—and reduction—gain of electrons. They play a pivotal role in energy generation and various industrial processes.

• Example: In the reaction \(\mathrm{Zn}(s) + \mathrm{CuSO_4}(aq) \rightarrow \mathrm{ZnSO_4}(aq) + \mathrm{Cu}(s)\), zinc is oxidized as it loses electrons to form \(\mathrm{Zn^{2+}}\), and copper is reduced as it gains electrons to form copper metal.


• Real-world Application: Redox reactions are fundamental in batteries like lithium-ion batteries, where oxidation and reduction reactions produce electrical energy.

The mnemonic "LEO says GER" ("Lose Electrons: Oxidation", "Gain Electrons: Reduction") can help remember which process is which. In redox reactions, it's important to identify both the oxidizing and reducing agents. The substance that gets reduced is the oxidizing agent, while the substance that gets oxidized is the reducing agent. Redox reactions are also critical in biological processes like cellular respiration and photosynthesis.