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Ch.19 - Electrochemistry
Chapter 19, Problem 48a

Balance the following half-reactions. (a) (acidic) Cr2O72-(aq) → Cr3+(aq)

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Key Concepts

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

Half-Reaction Method

The half-reaction method involves separating a redox reaction into its oxidation and reduction components. Each half-reaction is balanced for mass and charge, allowing for a clearer understanding of electron transfer. This method is particularly useful in acidic or basic solutions, where additional ions like H+ or OH- may be added to achieve balance.
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Balancing Redox Reactions in Acidic Medium

When balancing redox reactions in an acidic medium, one must account for hydrogen ions (H+) and water (H2O) to balance the number of atoms and charges. In the case of the given half-reaction, H+ ions are added to balance the oxygen atoms from the Cr2O7^2- ion, while water is used to balance any excess hydrogen atoms.
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Oxidation States

Oxidation states indicate the degree of oxidation of an atom in a compound, helping to identify which species are oxidized and reduced in a reaction. In the provided half-reaction, chromium changes from an oxidation state of +6 in Cr2O7^2- to +3 in Cr^3+, illustrating the reduction process. Understanding oxidation states is crucial for correctly balancing redox reactions.
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