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Ch.19 - Electrochemistry
McMurry - Chemistry 8th Edition
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All textbooksMcMurry 8th EditionCh.19 - ElectrochemistryProblem 42c
Chapter 19, Problem 42c

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (c) Cr(s) → Cr3+ (aq)

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Identify the change in oxidation state for chromium (Cr) in the given half-reaction.
Determine the initial oxidation state of Cr in its elemental form, Cr(s).
Determine the final oxidation state of Cr in the ion form, Cr^{3+} (aq).
Compare the initial and final oxidation states to see if there is an increase or decrease.
Classify the half-reaction: if the oxidation state increases, it is an oxidation; if it decreases, it is a reduction.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation and Reduction

Oxidation and reduction are chemical processes that involve the transfer of electrons between species. Oxidation refers to the loss of electrons, resulting in an increase in oxidation state, while reduction involves the gain of electrons, leading to a decrease in oxidation state. These processes are always coupled; when one species is oxidized, another must be reduced.
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Oxidation and Reduction Reactions

Oxidation States

Oxidation states (or oxidation numbers) are a way to keep track of electron transfer in chemical reactions. They indicate the degree of oxidation of an atom in a compound, with higher oxidation states reflecting a greater loss of electrons. In the half-reaction Cr(s) → Cr<sup>3+</sup> (aq), chromium transitions from an oxidation state of 0 in the solid state to +3 in the aqueous ion, indicating oxidation.
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Half-Reactions

Half-reactions are used to represent the oxidation and reduction processes separately in a redox reaction. Each half-reaction shows either the loss of electrons (oxidation) or the gain of electrons (reduction) and can be combined to balance the overall reaction. Identifying half-reactions helps in understanding the electron flow and the changes in oxidation states during the reaction.
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Related Practice
Textbook Question

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (b) Pt2+ (aq) → Pt(s)

Textbook Question

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (c) MnO4-(aq) → MnO42-(aq)

Textbook Question

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (b) H2O2(aq) → O2(g)

Textbook Question

Porous pellets of TiO2 can be reduced to titanium metal at the cathode of an electrochemical cell containing molten CaCl2 as the electrolyte. When the TiO2 is reduced, the O2-ions dis-solve in the CaCl2 and are subsequently oxidized to O2 gas at the anode. This approach may be the basis for a less expensive process than the one currently used for producing titanium.

(c) Write balanced equations for the anode, cathode, and overall cell reactions.

Textbook Question

Classify each of the following unbalanced half-reactions as either an oxidation or a reduction. (a) O2(g) → OH-(aq)

Textbook Question

Porous pellets of TiO2 can be reduced to titanium metal at the cathode of an electrochemical cell containing molten CaCl2 as the electrolyte. When the TiO2 is reduced, the O2-ions dis-solve in the CaCl2 and are subsequently oxidized to O2 gas at the anode. This approach may be the basis for a less expensive process than the one currently used for producing titanium.

(a) Label the anode and cathode, and indicate the signs of the electrodes.