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Chapter 20: Problem 14

(a) What is meant by the term reduction? (b) On which side of a reduction half-reaction do the electrons appear? (c) What is meant by the term reductant? (d) What is meant by the term reducing agent?

Short Answer

Expert verified
(a) Reduction is a chemical process where a substance gains electrons, resulting in a decrease of its oxidation state. (b) In a reduction half-reaction, electrons appear on the left-hand side (reactant side) of the equation. (c) A reductant, also known as a reducing agent, is a substance that donates electrons to another substance, causing the reduction of that substance. (d) A reducing agent is a substance that donates electrons to another substance, thus causing the reduction of that substance, and gets oxidized in the process.

Step by step solution

01

(a) Definition of reduction

Reduction is a chemical process in which a substance gains electrons, resulting in a decrease of its oxidation state. This process is the opposite of oxidation, in which a substance loses electrons and its oxidation state increases.
02

(b) Electrons in a reduction half-reaction

In a reduction half-reaction, electrons appear on the left-hand side (or reactant side) of the equation. This is because the substance undergoing reduction is gaining these electrons to achieve a lower oxidation state.
03

(c) Definition of reductant

A reductant, also known as a reducing agent, is a substance that donates electrons to another substance, thus causing the reduction of that substance. In a redox (reduction-oxidation) reaction, the reductant gets oxidized, while the substance it donates electrons to undergoes reduction.
04

(d) Definition of reducing agent

A reducing agent, also known as a reductant, is a substance that donates electrons to another substance, thus causing the reduction of that substance. Reducing agents play a crucial role in redox (reduction-oxidation) reactions, as they get oxidized while the substance they donate electrons to undergoes reduction.

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Most popular questions from this chapter

Hydrogen gas has the potential for use as a clean fuel in reaction with oxygen. The relevant reaction is $$ 2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) $$ Consider two possible ways of utilizing this reaction as an electrical energy source: (i) Hydrogen and oxygen gases are combusted and used to drive a generator, much as coal is currently used in the electric power industry; (ii) hydrogen and oxygen gases are used to generate electricity directly by using fuel cells that operate at \(85^{\circ} \mathrm{C} .\) (a) Use data in Appendix \(\mathrm{C}\) to calculate \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) for the reaction. We will assume that these values do not change appreciably with temperature. (b) Based on the values from part (a), what trend would you expect for the magnitude of \(\Delta G\) for the reaction as the temperature increases? (c) What is the significance of the change in the magnitude of \(\Delta G\) with temperature with respect to the utility of hydrogen as a fuel? (d) Based on the analysis here, would it be more efficient to use the combustion method or the fuel-cell method to generate electrical energy from hydrogen?

A voltaic cell is based on \(\mathrm{Cu}^{2+}(a q) / \mathrm{Cu}(s)\) and \(\mathrm{Br}_{2}(l) /\) \(\mathrm{Br}^{-}(a q)\) half-cells. (a) What is the standard emf of the cell? (b) Which reaction occurs at the cathode and which at the anode of the cell? (c) Use \(S^{\circ}\) values in Appendix \(\mathrm{C}\) and the relationship between cell potential and free-energy change to predict whether the standard cell potential increases or decreases when the temperature is raised above \(25^{\circ} \mathrm{C}\). (Thestandard entropy of \(\mathrm{Cu}^{2+}(a q)\) is $\left.S^{\circ}=-99.6 \mathrm{~J} / \mathrm{K}\right)$

(a) Assuming standard conditions, arrange the following in order of increasing strength as oxidizing agents in acidic solution: $\mathrm{MnO}_{4}^{-}(a q), \mathrm{O}_{3}(g), \mathrm{HSO}_{4}^{-}(a q), \mathrm{O}_{2}(g), \mathrm{HClO}(a q)$ (b) Arrange the following in order of increasing strength as reducing agents in basic solution: $\mathrm{Cr}(\mathrm{OH})_{3}(s), \mathrm{Fe}(s), \mathrm{Ca}(s),\( \)\mathrm{H}_{2}(g), \mathrm{Mn}(s)$

Iron corrodes to produce rust, \(\mathrm{Fe}_{2} \mathrm{O}_{3},\) but other corrosion products that can form are \(\mathrm{Fe}(\mathrm{O})(\mathrm{OH})\), iron oxyhydroxide, and magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4} .\) (a) What is the oxidation number of Fe in iron oxyhydroxide, assuming oxygen's oxidation number is \(-2 ?(\mathbf{b})\) The oxidation number for Fe in magnetite was controversial for a long time. If we assume that oxygen's oxidation number is \(-2,\) and Fe has a unique oxidation number, what is the oxidation number for Fe in magnetite? (c) It turns out that there are two different kinds of Fe in magnetite that have different oxidation numbers. Suggest what these oxidation numbers are and what their relative stoichiometry must be, assuming oxygen's oxidation number is -2 .

Metallic gold is collected from below the anode when a mixture of copper and gold metals is refined by electrolysis. Explain this behavior.
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