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Ch.20 - Electrochemistry
All textbooksBrown 15th EditionCh.20 - ElectrochemistryProblem 20a
Chapter 20, Problem 20a

Indicate whether the following balanced equations involve oxidation–reduction. If they do, identify the elements that undergo changes in oxidation number. (a) 2 AgNO3(aq) + CoCl2(aq) → 2 AgCl(s) + Co(NO3)2(aq)

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Determine the oxidation states of each element in the reactants and products.
For AgNO_3, Ag is +1, N is +5, and O is -2.
For CoCl_2, Co is +2, and Cl is -1.
For AgCl, Ag is +1, and Cl is -1.
For Co(NO_3)_2, Co is +2, N is +5, and O is -2.

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Key Concepts

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

Oxidation-Reduction Reactions

Oxidation-reduction (redox) reactions involve the transfer of electrons between substances, leading to changes in oxidation states. In these reactions, oxidation refers to the loss of electrons (increase in oxidation state), while reduction refers to the gain of electrons (decrease in oxidation state). Identifying whether a reaction is a redox process requires analyzing the oxidation states of the elements involved before and after the reaction.
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Oxidation States

Oxidation states (or oxidation numbers) are assigned to atoms in a compound to indicate their degree of oxidation or reduction. The rules for determining oxidation states include that the oxidation state of an element in its elemental form is zero, and for monoatomic ions, it equals the charge of the ion. Understanding how to assign oxidation states is crucial for identifying which elements are oxidized or reduced in a chemical reaction.
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Balancing Chemical Equations

Balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation, reflecting the law of conservation of mass. In redox reactions, balancing also involves ensuring that the total charge is the same on both sides. This process may require adjusting coefficients and can help in identifying the changes in oxidation states of the elements involved.
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Related Practice
Textbook Question

For each of the following balanced oxidation–reduction reactions, (i) identify the oxidation numbers for all the elements in the reactants and products and (ii) state the total number of electrons transferred in each reaction. (a) 2 MnO4-(aq) + 3 S2-(aq + 4 H2O(l) → 3 S(s) + 2 MnO2(s) + 8 OH-(aq) (b) 4 H2O2(aq) + Cl2O7(g) + 2 OH-(aq) → 2 ClO2-(aq) + 5 H2O(l) + 4 O2(g) (c) Ba2+(aq) + 2 OH-(aq) + H2O2(aq) + 2 ClO2(aq) → Ba(ClO2)2(s) + 2 H2O(l) + O2(g)

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Textbook Question

Indicate whether the following balanced equations involve oxidation–reduction. If they do, identify the elements that undergo changes in oxidation number. (a) PBr3(l) + 3 H2O(l) → H3PO3(aq) + 3 HBr(aq)

Textbook Question

Indicate whether the following balanced equations involve oxidation–reduction. If they do, identify the elements that undergo changes in oxidation number. (b) NaI(aq) + 3 HOCl(aq) → NaIO3(aq) + 3 HCl(aq) (c) 3 SO(1g) + 2 HNO3(aq) + 2 H2O(l) → 3 H2SO4(aq) + 2 NO(g)

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At 900 °C, titanium tetrachloride vapor reacts with molten magnesium metal to form solid titanium metal and molten magnesium chloride. (a) Write a balanced equation for this reaction.

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Hydrazine (N2H4) and dinitrogen tetroxide (N2O4) form a self-igniting mixture that has been used as a rocket propellant. The reaction products are N2 and H2O. (c) Which substance serves as the reducing agent and which as the oxidizing agent?

Textbook Question

Complete and balance the following half-reactions. In each case, indicate whether the half-reaction is an oxidation or a reduction. (a) Sn2+(aq) → Sn4+(aq) (acidic solution) (b) TiO2(s) → Ti2+(aq) (acidic solution) (c) ClO3-(aq) → Cl-(aq) (acidic solution) (d) N2(g) → NH4+(aq) (acidic solution)