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From each of the following pairs of substances, use data in Appendix E to choose the one that is the stronger reducing agent: $$ \begin{array}{l}{\text { (a) } \mathrm{Fe}(s) \text { or } \mathrm{Mg}(s)} \\\ {\text { (b) } \mathrm{Ca}(s) \text { or } \mathrm{Al}(s)} \\ {\text { (c) } \mathrm{H}_{2}\left(g, \text { acidic solution ) or } \mathrm{H}_{2} \mathrm{S}(g)\right.} \\ {\text { (d) } \mathrm{BrO}_{3}^{-}(a q) \text { or } \mathrm{IO}_{3}^{-}(a q)}\end{array} $$

Short Answer

Expert verified
The stronger reducing agents in each pair are: (a) \(\mathrm{Mg}(s)\) (b) \(\mathrm{Ca}(s)\) (c) \(\mathrm{H}_{2}(g)\) (d) \(\mathrm{IO}_{3}^{-}(aq)\)

Step by step solution

01

Find the standard reduction potentials for each substance

First, we need to look for the standard reduction potentials of the given substances in Appendix E. Here are the values we need: - Fe(s): \(\mathrm{Fe^{2+}} + 2\mathrm{e^{-}} \rightarrow \mathrm{Fe}(s)\) ; E掳 = -0.44 V - Mg(s): \(\mathrm{Mg^{2+}} + 2\mathrm{e^{-}} \rightarrow \mathrm{Mg}(s)\) ; E掳 = -2.37 V - Ca(s): \(\mathrm{Ca^{2+}} + 2\mathrm{e^{-}} \rightarrow \mathrm{Ca}(s)\) ; E掳 = -2.87 V - Al(s): \(\mathrm{Al^{3+}} + 3\mathrm{e^{-}} \rightarrow \mathrm{Al}(s)\) ; E掳 = -1.66 V - H2(g): \(\mathrm{2H^+} + 2\mathrm{e^{-}} \rightarrow \mathrm{H}_{2}(g)\) ; E掳 = 0.00 V - H2S(g): \(\mathrm{2H^+} + \mathrm{H}_{2}\mathrm{S} \rightarrow 2\mathrm{H}_{2}\mathrm{O} + \mathrm{S}\) ; E掳 = +0.14 V - BrO3鈦(aq): \(\mathrm{BrO}_{3}^{-} + 6\mathrm{H^+} + 6\mathrm{e^{-}} \rightarrow \mathrm{Br^{-}} + 3\mathrm{H}_{2}\mathrm{O}\) ; E掳 = +1.52 V - IO3鈦(aq): \(\mathrm{IO}_{3}^{-} + 6\mathrm{H^+} + 6\mathrm{e^{-}} \rightarrow \mathrm{I^{-}} + 3\mathrm{H}_{2}\mathrm{O}\) ; E掳 = +0.54 V
02

Compare the standard reduction potentials

Now, let's compare the standard reduction potentials in each pair to determine which substance is the stronger reducing agent: - For (a), \(\mathrm{Fe}(s)\) has an E掳 of -0.44 V, and \(\mathrm{Mg}(s)\) has an E掳 of -2.37 V. Since the reduction potential of \(\mathrm{Mg}(s)\) is more negative, it is a stronger reducing agent. - For (b), \(\mathrm{Ca}(s)\) has an E掳 of -2.87 V, and \(\mathrm{Al}(s)\) has an E掳 of -1.66 V. \(\mathrm{Ca}(s)\) has a more negative standard reduction potential, making it a stronger reducing agent. - For (c), \(\mathrm{H}_{2}(g)\) has an E掳 of 0.00 V, while \(\mathrm{H}_{2}\mathrm{S}(g)\) has an E掳 of +0.14 V. Since \(\mathrm{H}_{2}(g)\) has a more negative standard reduction potential, it is a stronger reducing agent. - For (d), \(\mathrm{BrO}_{3}^{-}(aq)\) has an E掳 of +1.52 V, and \(\mathrm{IO}_{3}^{-}(aq)\) has an E掳 of +0.54 V. Here, \(\mathrm{IO}_{3}^{-}(aq)\) has a more negative standard reduction potential, making it a stronger reducing agent.
03

Write the answers

Based on the standard reduction potentials, the stronger reducing agents in each pair are: (a) \(\mathrm{Mg}(s)\) (b) \(\mathrm{Ca}(s)\) (c) \(\mathrm{H}_{2}(g)\) (d) \(\mathrm{IO}_{3}^{-}(aq)\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Standard Reduction Potential
Understanding standard reduction potential is crucial for anyone studying redox reactions. It measures the tendency of a chemical species to acquire electrons and be reduced, expressed in volts (V). Each half-reaction in a redox process has an associated standard reduction potential, which is tabulated under standard conditions: a 25掳C temperature, 1M solution concentration, and a pressure of 1 atmosphere for gases.

A more negative standard reduction potential indicates a greater tendency for a substance to lose electrons and be oxidized, making it a stronger reducing agent. Conversely, a more positive potential suggests a substance is more likely to gain electrons and be reduced.

To compare different substances' reducing power, as in the exercise, you can use their standard reduction potential values. The substance with the more negative E掳 value is the stronger reducing agent. This concept not only aids in solving homework problems but also has practical applications, such as in the design of batteries and electroplating processes.
Electrochemical Series
The electrochemical series, also known as the activity series, is a list of elements organized according to their standard reduction potential. At the top of the series are the elements with the most positive reduction potential, considered the weakest reducing agents. As you move down the series, the reduction potential becomes more negative, and the strength of the reducing agents increases.

This series is a powerful tool for predicting the outcome of chemical reactions. It helps in determining which elements will displace others in a chemical reaction. For instance, in the textbook exercise, by referring to the electrochemical series, it becomes apparent why magnesium (Mg) is a stronger reducing agent than iron (Fe), as magnesium appears lower in the series due to its more negative standard reduction potential.
Redox Reactions
Redox reactions are a family of reactions where reduction and oxidation occur simultaneously. Reduction involves the gain of electrons, while oxidation involves the loss of electrons. To remember this, you can use the mnemonic 'OIL RIG'鈥擮xidation Is Loss, Reduction Is Gain.

These reactions are fundamental to numerous processes in chemistry and biology, including cellular respiration and the functioning of batteries. Understanding which substances act as reducing agents or oxidizing agents is essential. Reducing agents donate electrons and are themselves oxidized, while oxidizing agents accept electrons and are reduced. In the context of our textbook exercise, once you grasp the concept of standard reduction potentials, you can easily identify the stronger reducing agent in a pair by looking at which substance will more readily donate electrons.

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Most popular questions from this chapter

(a) How many coulombs are required to plate a layer of chromium metal 0.25 \(\mathrm{mm}\) thick on an auto bumper with a total area of 0.32 \(\mathrm{m}^{2}\) from a solution containing \(\mathrm{CrO}_{4}^{2-}\) ? The density of chromium metal is 7.20 \(\mathrm{g} / \mathrm{cm}^{3} .\) (b) What current flow is required for this electroplating if the bumper is to be plated in 10.0 s? (c) If the external source has an emf of \(+6.0 \mathrm{V}\) and the electrolytic cell is 65\(\%\) efficient, how much electrical power is expended to electroplate the bumper?

The electrodes in a silver oxide battery are silver oxide \(\left(\mathrm{Ag}_{2} \mathrm{O}\right)\) and zinc. (a) Which electrode acts as the anode? (b) Which battery do you think has an energy density most similar to the silver oxide battery: a Li-ion battery, a nickel-cadmium battery, or a lead-acid battery? [ Section 20.7]

Aqueous solutions of ammonia \(\left(\mathrm{NH}_{3}\right)\) and bleach (active ingredient \(\mathrm{NaOCl}\) ) are sold as cleaning fluids, but bottles of both of them warn: "Never mix ammonia and bleach, as toxic gases may be produced." One of the toxic gases that can be produced is chloroamine, \(\mathrm{NH}_{2} \mathrm{Cl} .\) (a) What is the oxidation number of chlorine in bleach? (b) What is the oxidation number of chlorine in chloramine? (c) Is Cl oxidized, reduced, or neither, upon the conversion of bleach to chloramine? (d) Another toxic gas that can be produced is nitrogen trichloride, \(\mathrm{NCl}_{3} .\) What is the oxidation number of \(\mathrm{N}\) in nitrogen trichloride? (e) Is \(\mathrm{N}\) oxidized, reduced,or neither, upon the conversion of ammonia to nitrogen trichloride?

If the equilibrium constant for a two-electron redox reaction at 298 \(\mathrm{K}\) is \(1.5 \times 10^{-4}\) , calculate the corresponding \(\Delta G^{\circ}\) and \(E^{\circ} .\)

The standard reduction potential of \(\mathrm{Eu}^{2+}(a q)\) is \(-0.43 \mathrm{V}\) . Using Appendix E, which of the following substances is capable of reducing Eu' \((a q)\) to \(\mathrm{Eu}^{2+}(a q)\) under standard conditions: Al, Co, \(\mathrm{H}_{2} \mathrm{O}_{2}, \mathrm{N}_{2} \mathrm{H}_{5}^{+}, \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} ?\)

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