Rocks in Caves The stalactites and stalagmites in most caves...

Rocks in Caves The stalactites and stalagmites in most caves are made of limestone (calcium carbonate; see Figure 4.14 ). However, in the Lower Kane Cave in Wyoming they are made of gypsum (calcium sulfate). The presence of $\mathrm{CaSO}_{4}$ is explained by the following sequence of reactions: $$ \mathrm{H}_{2} \mathrm{S}(a q)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{4}(a q) $$ $\mathrm{H}_{2} \mathrm{SO}_{4}(a q)+\mathrm{CaCO}_{3}(s) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{CO}_{2}(g)$ a. Which (if either) of these reactions is a redox reaction? How many electrons are transferred? b. Write a net ionic equation for the reaction of $\mathrm{H}_{2} \mathrm{SO}_{4}$ with $\mathrm{CaCO}_{3}$ c. How would the net ionic equation be different if the reaction were written as follows? $\mathrm{H}_{2} \mathrm{SO}_{4}(a q)+\mathrm{CaCO}_{3}(s) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{CO}_{3}(a q)$

Rocks in Caves The stalactites and stalagmites in most caves are made of limestone (calcium carbonate; see Figure 4.14 ). However, in the Lower Kane Cave in Wyoming they are made of gypsum (calcium sulfate). The presence of $\mathrm{CaSO}_{4}$ is explained by the following sequence of reactions:
$$
\mathrm{H}_{2} \mathrm{S}(a q)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{4}(a q)
$$
$\mathrm{H}_{2} \mathrm{SO}_{4}(a q)+\mathrm{CaCO}_{3}(s) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{CO}_{2}(g)$
a. Which (if either) of these reactions is a redox reaction? How many electrons are transferred?
b. Write a net ionic equation for the reaction of $\mathrm{H}_{2} \mathrm{SO}_{4}$ with $\mathrm{CaCO}_{3}$
c. How would the net ionic equation be different if the reaction were written as follows?
$\mathrm{H}_{2} \mathrm{SO}_{4}(a q)+\mathrm{CaCO}_{3}(s) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{CO}_{3}(a q)$

Key Concepts

Redox Reactions

Redox reactions, or oxidation-reduction reactions, are chemical processes in which electrons are transferred between species. In these reactions, one substance is oxidized (loses electrons) and another is reduced (gains electrons). Identifying a redox reaction involves checking for changes in oxidation states of the elements involved. This concept is central to understanding reaction mechanisms where electron transfer leads to the formation of new products, as exhibited by the oxidation of H2S in the provided example.

Electron Transfer

Electron transfer is the core process in redox reactions where electrons move from one molecule or ion to another. The number of electrons transferred helps quantify the change in oxidation states, providing insight into the reaction’s balance and energetics. Determining the count of electrons exchanged is fundamental in redox chemistry as it affects stoichiometry and the overall feasibility of the reaction.

Net Ionic Equations

Net ionic equations simplify chemical reactions by showing only the species that undergo change, omitting spectator ions that remain unchanged in solution. This concept helps in focusing on the reactive participants and the actual chemical transformation, whether it involves formation of a precipitate, a gas, or a weak electrolyte. Writing a net ionic equation clarifies the underlying chemistry, such as the reaction between acid and carbonate where only the reactive ions and compounds are reflected.

Acid-Carbonate Reactions

Acid-carbonate reactions involve an acid reacting with a carbonate compound, typically yielding a salt, water, and carbon dioxide. This reaction mechanism is an excellent example of how acids donate protons to the carbonate ion, leading to the decomposition of carbonic acid into CO2 and H2O. Understanding acid-carbonate reactions is important for grasping fundamental acid–base chemistry and reaction dynamics in geological and natural processes, as illustrated by the different net ionic equations in the example.

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