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Ch.4 - Reactions in Aqueous Solution
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.4 - Reactions in Aqueous SolutionProblem 51c,d
Chapter 4, Problem 51c,d

Which element is oxidized, and which is reduced in the following reactions? (c) Cl2(aq) + 2 NaI(aq) → I2(aq) + 2 NaCl(aq) (d) PbS(s) + 4 H2O2(aq) → PbSO4(s) + 4 H2O(l)

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1
Identify the oxidation states of each element in the reactants and products. For Cl2, chlorine is in the 0 oxidation state. In NaI, iodine is in the -1 oxidation state. In I2, iodine is in the 0 oxidation state. In NaCl, chlorine is in the -1 oxidation state.
Compare the oxidation states of each element before and after the reaction to determine the changes in oxidation state. Chlorine goes from 0 in Cl2 to -1 in NaCl, indicating a gain of electrons. Iodine goes from -1 in NaI to 0 in I2, indicating a loss of electrons.
Recall that oxidation is the loss of electrons and reduction is the gain of electrons. Since iodine loses electrons, it is oxidized. Since chlorine gains electrons, it is reduced.
Write the half-reactions to clearly show the electron transfer. The oxidation half-reaction for iodine can be written as: 2 I- -> I2 + 2 e-. The reduction half-reaction for chlorine can be written as: Cl2 + 2 e- -> 2 Cl-.
Conclude that in the reaction Cl2 + 2 NaI -> I2 + 2 NaCl, iodine (I) is oxidized and chlorine (Cl) is reduced.

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 substances. 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 always occur simultaneously in a redox reaction.
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Oxidation and Reduction Reactions

Oxidation States

Oxidation states (or oxidation numbers) are assigned to atoms in a compound to indicate their degree of oxidation or reduction. The oxidation state helps in identifying which element is oxidized and which is reduced during a reaction. For example, in the reaction provided, the oxidation states of chlorine and iodine change, allowing us to determine the electron transfer.
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Oxidation Numbers

Half-Reactions

Half-reactions are used to separate the oxidation and reduction processes in a redox reaction. Each half-reaction shows either the loss of electrons (oxidation) or the gain of electrons (reduction) for a specific species. By analyzing the half-reactions, one can clearly identify which elements are oxidized and reduced in the overall reaction.
Related Practice
Textbook Question

Which of the following are redox reactions? For those that are, indicate which element is oxidized and which is reduced. For those that are not, indicate whether they are precipitation or neutralization reactions. (a) P4(s) + 10 HClO(aq) + 6 H2O(l) → 4 H3PO4(aq) + 10 HCl(aq) (b) Br2(l) + 2 K(s)→ 2 KBr(s) (c) CH3CH2OH(l) + 3 O2(g) → 3 H2O(l) + 2 CO2(g) (d) ZnCl2(aq) + 2 NaOH(aq) → Zn(OH)2(s) + 2 NaCl(aq)

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Textbook Question

Determine the oxidation number for the indicated element in each of the following substances: (e) Pt in PtCl4 (f) O in OF2.

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Which element is oxidized, and which is reduced in the following reactions? (a) N2(g) + 3 H2(g) → 2 NH3(g)

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Write balanced molecular and net ionic equations for the reactions of (a) manganese with dilute sulfuric acid (b) chromium with hydrobromic acid (c) tin with hydrochloric acid (d) aluminum with formic acid, HCOOH.

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Write balanced molecular and net ionic equations for the reactions of (a) hydrochloric acid with nickel (b) dilute sulfuric acid with iron

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Determine the oxidation number for the indicated element in each of the following substances: (f) Cl in NaClO4.

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