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Chapter 13: Problem 25

Arrange the following metals in order of increasing strength as reducing agents for species in aqueous solution: (a) \(\mathrm{Cu}, \mathrm{Zn}, \mathrm{Cr}\), Fe; (b) Li, Na, K, Mg; (c) U, V, Ti, Al; (d) Ni, Sn, Au, Ag.

Short Answer

Expert verified
(a) Cu < Fe < Zn < Cr, (b) Mg < Li < Na < K, (c) U < V < Ti < Al, (d) Au < Ag < Sn < Ni.

Step by step solution

01

Understand the Concept of a Reducing Agent

A reducing agent is an element that donates electrons to another species in a chemical reaction, thereby reducing the oxidation state of that species. In metallurgy, metals that are good reducing agents can easily lose electrons to form positive ions. The strength of a metal as a reducing agent increases with its activity, which typically increases from lower to higher positions within a group on the periodic table and from right to left across a period.
02

Refer to the Activity Series of Metals

The activity series of metals lists metals from highest to lowest reactivity. Metals higher in the series are stronger reducing agents. To solve the exercise, the metals need to be arranged based on their positions in the activity series.
03

Arrange Series (a) in Order

For series (a) \(\mathrm{Cu}, \mathrm{Zn}, \mathrm{Cr}, \mathrm{Fe}\), using the activity series, the order of increasing strength as reducing agents is \(\mathrm{Cu} < \mathrm{Fe} < \mathrm{Zn} < \mathrm{Cr}\).
04

Arrange Series (b) in Order

For series (b) \(\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Mg}\), based on their positions in the activity series, the order is \(\mathrm{Mg} < \mathrm{Li} < \mathrm{Na} < \mathrm{K}\). Note that lithium is above sodium and potassium despite being in the same group, due to its exceptional reactivity.
05

Arrange Series (c) in Order

For series (c) \(\mathrm{U}, \mathrm{V}, \mathrm{Ti}, \mathrm{Al}\), the correct sequence from weakest to strongest reducing agent according to the activity series is \(\mathrm{U} < \mathrm{V} < \mathrm{Ti} < \mathrm{Al}\).
06

Arrange Series (d) in Order

For series (d) \(\mathrm{Ni}, \mathrm{Sn}, \mathrm{Au}, \mathrm{Ag}\), the activity series tells us the order of increasing strength as reducing agents is \(\mathrm{Au} < \mathrm{Ag} < \mathrm{Sn} < \mathrm{Ni}\).

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Key Concepts

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

Activity Series of Metals
Understanding the activity series of metals is crucial when working with redox reactions, specifically when identifying the strength of reducing agents. The activity series is a chart that organizes metals by their ability to displace hydrogen from water and acids. It can also be thought of as a ranking based on how easily a metal can be oxidized.
  • Metal Reactivity: Highly reactive metals like lithium and potassium are at the top of this series and are excellent reducing agents because they lose electrons readily.
  • Less Reactive Metals: Towards the bottom of the series are metals like gold and silver, which hold onto their electrons more tightly and are less likely to act as reducing agents in reactions.

The concept of the activity series also helps us to predict the outcomes of single displacement reactions, where one metal displaces another from a compound. Metals higher in the series will replace metals lower in the series from their compounds in solution.
Chemical Reactivity
Chemical reactivity refers to the tendency of a substance to engage in chemical reactions. For metals, this often involves losing electrons to form cations — a process known as oxidation. Understanding chemical reactivity is essential not only for predicting product formation but also for determining reaction conditions, such as temperature and concentration that might affect the reaction's rate and direction.
  • Factors Influencing Reactivity: For metals, reactivity is influenced by their atomic structure, particularly the ease with which they can lose outer electrons.
  • Environmental Conditions: External factors like temperature and the presence of catalysts can also affect the reactivity of metals.

When studying redox chemistry, it's important to recognize that reducing agents are themselves oxidized. A good understanding of chemical reactivity can thus provide insight into why certain substances act as either oxidizing or reducing agents.
Oxidation-Reduction Reactions
Oxidation-reduction reactions, commonly known as redox reactions, are processes where electron transfer occurs between reactants, leading to changes in their oxidation states. These reactions are fundamental to numerous applications, including energy production, corrosion, and biochemical processes.
  • Oxidation: Represents the loss of electrons. The substance that loses electrons is called the reducing agent because it 'reduces' the charge of another species by donating electrons to it.
  • Reduction: Refers to the gain of electrons. The oxidizing agent is the species that gains electrons and is thereby reduced in the process.

In the context of the given exercise, metals that are better reducing agents will more readily give up electrons. When arranging metals by their strength as reducing agents, we look for their propensity to lose electrons, with the metal that loses electrons most easily being the strongest reducing agent.

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Most popular questions from this chapter

Consider the cell \(\mathrm{Ag}(\mathrm{s})\left|\mathrm{Ag}^{+}\left(\mathrm{aq}, 5.0 \mathrm{mmol} \cdot \mathrm{L}^{-1}\right)\right| \mid \mathrm{Ag}^{+}(\mathrm{aq}\), \(\left.0.15 \mathrm{~mol} \cdot \mathrm{L}^{-1}\right) \mid \mathrm{Ag}(\mathrm{s})\). Can this cell do work? If so, what is the maximum work that it can perform (per mole of \(\mathrm{Ag}\) )?

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in acidic solution. Identify the oxidizing agent and reducing agent in cach reaction. (a) Reaction of the selenite ion with chlorate ion: $$ \mathrm{SeO}_{3}{ }^{2-}(\mathrm{s})+\mathrm{ClO}_{3}{ }^{-}(\mathrm{aq}) \longrightarrow \mathrm{SeO}_{4}{ }^{2-}(\mathrm{aq})+\mathrm{Cl}_{2}(\mathrm{~g}) $$ (b) Formation of propanone (acetone), which is used in nail polish remover, from isopropanol (rubbing alcohol) by the action of dichromate ion: $$ \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}(\mathrm{aq})+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq}) \rightarrow \mathrm{Cr}^{3+}(\mathrm{aq})+\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(\mathrm{aq}) $$ (c) Reaction of gold with selenic acid: \(\mathrm{Au}(\mathrm{s})+\mathrm{SeO}_{4}{ }^{2-}(\mathrm{aq}) \longrightarrow \mathrm{Au}^{3+}(\mathrm{aq})+\mathrm{SeO}_{3}{ }^{2-}\) (aq) (d) Preparation of stibnine from antimonic acid: \(\mathrm{H}_{2} \mathrm{SbO}_{3}{ }^{2-}(\mathrm{s})+\mathrm{Zn}(\mathrm{s}) \longrightarrow \mathrm{SbH}_{3}(\mathrm{aq})+\mathrm{Zn}^{2+}(\mathrm{aq})\)

What range (in volts) does a voltmeter need to have in order to measure \(\mathrm{pH}\) in the range of 1 to 14 at \(25^{\circ} \mathrm{C}\) if the voltage is zero when \(\mathrm{pH}=7\) ?

(a) Suggest two metals that could be used for the cathodic protection of a titanium pipeline. (b) What factors other than relative positions in the electrochemical series need to be considered in practice? (c) Often copper piping is connected to iron pipes in household plumbing systems. What is a possible effect of the copper on the iron pipes?

\( \mathrm{~A} 1.0 \mathrm{M} \mathrm{KBr}(\mathrm{aq})\) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential or passivity at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis?
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