Chemistry The Molecular Science

John W. Moore, Conrad L. Stanitski

Chapter 17

Electrochemistry and Its Applications - all with Video Answers

Educators

Chapter Questions

Problem 1

Make a drawing showing the principal parts of
(a) a voltaic cell: show the anode, the cathode, the direction of electron movement outside the cell, and the direction of ion movement inside the cell.
(b) a standard hydrogen electrode: describe the components of the electrode and explain how it works.

Aadit Sharma

Aadit Sharma

Numerade Educator

Problem 2

Explain how product-favored electrochemical reactions can be used to do useful work.

Anthony Han

Numerade Educator

Problem 3

Explain how reactant-favored electrochemical reactions can be induced to make products.

Anthony Han

Numerade Educator

Problem 4

Explain how electroplating works.

Aadit Sharma

Numerade Educator

Problem 5

Identify each statement as true or false. Rewrite each false statement to make it true.
(a) Oxidation always occurs at the anode of an electrochemical cell.
(b) The anode of a discharging voltaic cell is the site of reduction and is negative.
(c) Standard-state conditions for electrochemical cells are a concentration of $1.0 \mathrm{M}$ for dissolved species and a pressure of 1 bar for gases.
(d) The potential of a voltaic cell does not change with temperature.
(e) All product-favored oxidation-reduction reactions have a standard cell potential $E_{\text {cell }}^{\circ}$, with a negative sign.

Anthony Han

Numerade Educator

Problem 6

In this reaction, assign an oxidation number to each atom in reactants and products. Identify which substance is oxidized and which is reduced. Identify the oxidizing agent and the reducing agent.
$$
\begin{aligned}
8 \mathrm{H}^{+}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq})+& 5 \mathrm{Fe}^{2+}(\mathrm{aq}) \longrightarrow \\
& 5 \mathrm{Fe}^{3+}(\mathrm{aq})+\mathrm{Mn}^{2+}(\mathrm{aq})+4 \mathrm{H}_{2} \mathrm{O}(\ell)
\end{aligned}
$$

Anthony Han

Numerade Educator

Problem 7

In each of these reactions assign an oxidation number to each atom in reactants and products. Identify which substance is oxidized and which is reduced. Identify the oxidizing agent and the reducing agent.
(a) $\mathrm{Fe}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow \mathrm{FeBr}_{2}(\mathrm{~s})$
(b) $2 \mathrm{Al}(\mathrm{s})+3 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{AlCl}_{3}(\mathrm{~s})$
(c) $8 \mathrm{HI}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow$
$$
\mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})+4 \mathrm{I}_{2}(\mathrm{~s})+4 \mathrm{H}_{2} \mathrm{O}(\ell)
$$

Aadit Sharma

Numerade Educator

Problem 8

Choose four elements: a metal that is a representative element, a transition metal, a nonmetal, and a metalloid. Using the index to this text, find a chemical reaction in which each element occurs as a reactant. Assign oxidation numbers to all elements on the reactant and product sides, and identify the oxidizing agent and the reducing agent.

Aadit Sharma

Numerade Educator

Problem 9

Answer Question 8 again, but this time find a chemical reaction in which each element is produced.

Aadit Sharma

Numerade Educator

Problem 10

Write half-reactions for these changes:
(a) Oxidation of cadmium to $\mathrm{Cd}^{2+}$ ions
(b) Reduction of $\mathrm{Fe}^{3+}$ ions to Fe metal
(c) Reduction of $\mathrm{Sn}^{4+}$ ions to $\mathrm{Sn}^{2+}$ ions
(d) Reduction of chlorine to $\mathrm{Cl}^{-}$ ions
(e) Oxidation of sulfur dioxide to sulfate ions in acidic solution

Anthony Han

Numerade Educator

Problem 11

Write half-reactions for these changes:
(a) Reduction of $\mathrm{MnO}_{4}^{-}$ ion to $\mathrm{Mn}^{2+}$ ion in acid solution
(b) Reduction of $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ ion to $\mathrm{Cr}^{3+}$ ion in acid solution
(c) Oxidation of chlorine gas to $\mathrm{ClO}^{-}$ ions
(d) Reduction of hydrogen peroxide to water in acidic solution
(e) Oxidation of nitrous acid to nitrate ions in acidic solution

Anthony Han

Numerade Educator

Problem 12

For the reaction in Question $6,$ write balanced half reactions.

Aadit Sharma

Numerade Educator

Problem 13

For each reaction in Question $7,$ write balanced half reactions.

David Collins

Numerade Educator

Problem 14

For the reaction in Question $6,$ combine the balanced half-reactions you wrote in Question 12 to give a balanced overall equation.

Aadit Sharma

Numerade Educator

Problem 15

For each reaction in Question $7,$ combine the balanced half-reactions you wrote in Question 13 to give a balanced overall equation.

David Collins

Numerade Educator

Problem 16

Balance these redox reactions, and identify the oxidizing agent and the reducing agent.
(a) $\mathrm{CO}(\mathrm{g})+\mathrm{O}_{3}(\mathrm{~g}) \longrightarrow \mathrm{CO}_{2}(\mathrm{~g})$
(b) $\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{HCl}(\mathrm{g})$
(c) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+\mathrm{Ti}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{TiO}_{2}(\mathrm{~s})$ in acidic
solution
(d) $\mathrm{Cl}^{-}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq}) \longrightarrow \mathrm{Cl}_{2}(\mathrm{~g})+\mathrm{MnO}_{2}(\mathrm{~s})$ in acidic
solution
(e) $\mathrm{FeS}_{2}(\mathrm{~s})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})+\mathrm{SO}_{2}(\mathrm{~g})$
(f) $\mathrm{O}_{3}(\mathrm{~g})+\mathrm{NO}(\mathrm{g}) \longrightarrow \mathrm{O}_{2}(\mathrm{~g})+\mathrm{NO}_{2}(\mathrm{~g})$
(g) $\mathrm{Zn}(\mathrm{s})+\mathrm{HgO}(\mathrm{s}) \longrightarrow \mathrm{Zn}(\mathrm{OH})_{2}(\mathrm{~s})+\operatorname{Hg}(\ell)$ in basic solution

Aadit Sharma

Numerade Educator

Problem 17

Balance these redox reactions, and identify the oxidizing agent and the reducing agent.
(a) $\mathrm{FeO}(\mathrm{s})+\mathrm{O}_{3}(\mathrm{~g}) \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})$
(b) $\mathrm{P}_{4}(\mathrm{~s})+\mathrm{Br}_{2}(\ell) \longrightarrow \mathrm{PBr}_{5}(\ell)$
(c) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+\mathrm{Co}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{Co}^{3+}(\mathrm{aq})$ in
acidic solution
(d) $\mathrm{Cl}^{-}(\mathrm{aq})+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq}) \longrightarrow \mathrm{Cl}_{2}(\mathrm{~g})+\mathrm{Cr}^{3+}(\mathrm{aq})$ in acidic
solution
(e) $\mathrm{MnO}_{4}^{-}(\mathrm{aq})+\mathrm{Zn}(\mathrm{s}) \longrightarrow \mathrm{MnO}_{2}(\mathrm{~s})+\mathrm{Zn}(\mathrm{OH})_{2}(\mathrm{~s})$ in basic solution
(f) $\mathrm{H}_{2} \mathrm{CO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell)$
(g) $\mathrm{C}_{3} \mathrm{H}_{8}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell)$

Aadit Sharma

Numerade Educator

Problem 18

For the reaction $\mathrm{Cu}^{2+}(\mathrm{aq})+\mathrm{Zn}(\mathrm{s}) \longrightarrow \mathrm{Cu}(\mathrm{s})+\mathrm{Zn}^{2+}(\mathrm{aq})$
why can't you generate electric current by placing a piece of copper metal and a piece of zinc metal in a solution containing $\mathrm{CuCl}_{2}(\mathrm{aq})$ and $\mathrm{ZnCl}_{2}(\mathrm{aq})$ ?

Aadit Sharma

Numerade Educator

Problem 19

Explain the function of a salt bridge in a voltaic cell.

LJ

Lena Jake

Numerade Educator

Problem 20

Tell whether this statement is true or false. If false, rewrite it to make it a correct statement: The value of an electrode potential changes when the half-reaction is multiplied by a factor. That is, $E^{\circ}$ for $\mathrm{Li}^{+}+\mathrm{e}^{-} \longrightarrow \mathrm{Li}$ is different from that for $2 \mathrm{Li}^{+}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Li}$.

Anthony Han

Numerade Educator

Problem 21

Tell whether this statement is true or false. If false, rewrite it to make it a correct statement: The value electrode potential changes when the half-reaction is multiplied by a factor. That is, $E^{\circ}$ for $\mathrm{Li}^{+}+\mathrm{e}^{-}$

Anthony Han

Numerade Educator

Problem 22

A voltaic cell is assembled with $\mathrm{Sn}(\mathrm{s})$ and $\mathrm{Sn}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$
in one compartment and $\mathrm{Ag}(\mathrm{s})$ and $\mathrm{AgNO}_{3}(\mathrm{aq})$ in the other. An external wire connects the two electrodes, and a salt bridge containing $\mathrm{KNO}_{3}($ aq) connects the two solutions.
(a) In the product-favored reaction, $\mathrm{Ag}^{+}$ is reduced to silver metal. Write a balanced net ionic equation for this reaction.
(b) Which half-reaction occurs at each electrode? Which is the anode and which is the cathode?
(c) Draw a diagram of the cell, indicating the direction of electron movement outside the cell and of ion movement within the cell.

Aadit Sharma

Numerade Educator

Problem 23

Draw a diagram of each cell. Label the anode, the cathode, the species in each half-cell solution, the direction of electron movement in an external circuit, and the direction of movement of ions within the cell.
(a) $\mathrm{Cu}(\mathrm{s})\left|\mathrm{Cu}^{2+}(\mathrm{aq}) \| \mathrm{Fe}^{2+}(\mathrm{aq})\right| \mathrm{Fe}(\mathrm{s})$
(b) $\mathrm{Pt}(\mathrm{s})\left|\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}), \mathrm{H}^{+}(\mathrm{aq}) \| \mathrm{Fe}^{2+}(\mathrm{aq}), \mathrm{Fe}^{3+}(\mathrm{aq})\right| \mathrm{Pt}(\mathrm{s})$

Aadit Sharma

Numerade Educator

Problem 24

You light a $25-W$ light bulb with the current from a $12-V$ lead-acid storage battery. Calculate how much energy the light bulb utilized after $1.0 \mathrm{~h}$ of operation. Calculate how many coulombs passed through the bulb. Assume $100 \%$ efficiency. $(1 \mathrm{~W}=1 \mathrm{~J} / \mathrm{s} .)$

Anthony Han

Numerade Educator

Problem 25

Copper can reduce silver ion to metallic silver, a reaction that could, in principle, be used in a battery.
$$
\mathrm{Cu}(\mathrm{s})+2 \mathrm{Ag}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Cu}^{2+}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})
$$
(a) Write equations for the half-reactions involved.
(b) Which half-reaction is an oxidation and which is a reduction? Which half-reaction occurs in the anode compartment and which takes place in the cathode compartment?

Anthony Han

Numerade Educator

Problem 26

Chlorine gas can oxidize zinc metal in a reaction that has been suggested as the basis of a battery. Write the half reactions involved. Label which is the oxidation half reaction and which is the reduction half-reaction.

Anthony Han

Numerade Educator

Problem 27

In Table 17.1 ( $\in$ Sec. $17-5$ ), identify (a) the strongest oxidizing agent; (b) the strongest reducing agent; (c) the weakest oxidizing agent; and (d) the weakest reducing agent.

Aadit Sharma

Numerade Educator

Problem 28

One of the most energetic redox reactions is that between $\mathrm{F}_{2}$ gas and lithium metal.
(a) Write the half-reactions involved. Label the oxidation half-reaction and the reduction half-reaction.
(b) Using data from Table $17.1,$ calculate $E_{\text {cell }}^{\circ}$ for this reaction.

Aadit Sharma

Numerade Educator

Problem 29

Using the standard half-cell potentials in Table 17.1 , place these elements in order of increasing ability to function as reducing agents:
(a) $\mathrm{Cl}_{2}$
(b) $\mathrm{Fe}$
(c) $\mathrm{Ag}$
(d) $\mathrm{Na}$
(e) $\mathrm{H}_{2}$

Aadit Sharma

Numerade Educator

Problem 30

Using the standard half-cell potentials in Table 17.1 place these elements in order of increasing ability to function as oxidizing agents:
(a) $\mathrm{O}_{2}$
(b) $\mathrm{H}_{2} \mathrm{O}_{2}$
(c) $\mathrm{PbSO}_{4}$
(d) $\mathrm{H}_{2} \mathrm{O}$

Aadit Sharma

Numerade Educator

Problem 31

Calculate the value of $E_{\text {cell }}^{\circ}$ for each of these reactions. Decide whether each is product-favored.
(a) $\mathrm{I}_{2}(\mathrm{~s})+\mathrm{Mg}(\mathrm{s}) \longrightarrow \mathrm{Mg}^{2+}(\mathrm{aq})+2 \mathrm{I}^{-}(\mathrm{aq})$
(b) $\mathrm{Ag}(\mathrm{s})+\mathrm{Fe}^{3+}(\mathrm{aq}) \longrightarrow \mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{Fe}^{2+}(\mathrm{aq})$
(c) $\mathrm{Sn}^{2+}(\mathrm{aq})+2 \mathrm{Ag}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Sn}^{4+}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})$
(d) $2 \mathrm{Zn}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{Zn}^{2+}(\mathrm{aq})+4 \mathrm{OH}^{-}$ (aq)

Anthony Han

Numerade Educator

Problem 32

Consider these half-reactions:
$$
\begin{array}{lr}
\hline \text { Half-reaction } & E^{\circ}(\mathrm{V}) \\
\hline \mathrm{Au}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Au}(\mathrm{s}) & 1.52 \\
\mathrm{Pt}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pt}(\mathrm{s}) & 1.118 \\
\mathrm{Co}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Co}(\mathrm{s}) & -0.277 \\
\mathrm{Mn}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Mn}(\mathrm{s}) & -1.18 \\
\hline
\end{array}
$$
(a) Which is the weakest oxidizing agent?
(b) Which is the strongest oxidizing agent?
(c) Which is the strongest reducing agent?
(d) Which is the weakest reducing agent?
(e) Will $\mathrm{Co}(\mathrm{s})$ reduce $\mathrm{Pt}^{2+}(\mathrm{aq})$ to $\mathrm{Pt}(\mathrm{s})$ ?
(f) Will $\mathrm{Pt}(\mathrm{s})$ reduce $\mathrm{Co}^{2+}(\mathrm{aq})$ to $\mathrm{Co}(\mathrm{s})$ ?
(g) Which ions can be reduced by Co(s)?

Aadit Sharma

Numerade Educator

Problem 33

Consider these half-reactions:
$$
\begin{array}{lr}
\hline \text { Half-reaction } & E^{\circ}(\mathrm{V}) \\
\hline \mathrm{Ce}^{4+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \mathrm{Ce}^{3+}(\mathrm{aq}) & 1.72 \\
\mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \mathrm{Ag}(\mathrm{s}) & 0.80 \\
\mathrm{Hg}_{2}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Hg}(\ell) & 0.80 \\
\mathrm{Sn}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Sn}(\mathrm{s}) & -0.14 \\
\mathrm{Ni}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Ni}(\mathrm{s}) & -0.25 \\
\mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s}) & -1.68 \\
\hline
\end{array}
$$
(a) Which is the weakest oxidizing agent?
(b) Which is the strongest oxidizing agent?
(c) Which is the strongest reducing agent?
(d) Which is the weakest reducing agent?
(e) Will $\mathrm{Sn}(\mathrm{s})$ reduce $\mathrm{Ag}^{+}(\mathrm{aq})$ to $\mathrm{Ag}(\mathrm{s}) ?$
(f) Will $\mathrm{Hg}(\ell)$ reduce $\mathrm{Sn}^{2+}(\mathrm{aq})$ to $\mathrm{Sn}(\mathrm{s}) ?$
(g) Name the ions that can be reduced by $\operatorname{Sn}(\mathrm{s})$.
(h) Which metals can be oxidized by $\mathrm{Ag}^{+}(\mathrm{aq}) ?$

Aadit Sharma

Numerade Educator

Problem 34

In principle, a battery could be made from aluminum metal and chlorine gas.
(a) Write a balanced equation for the reaction that would occur in a battery using $\mathrm{Al}^{3+}(\mathrm{aq}) \mid \mathrm{Al}(\mathrm{s})$ and $\mathrm{Cl}_{2}(\mathrm{~g}) \mid \mathrm{Cl}^{-}($ aq $)$ half-cells.
(b) Identify the half-reaction at the anode and at the cathode. Do electrons flow from the $\mathrm{Al}$ electrode when the cell does work? Explain.
(c) Calculate the standard potential, $E_{\text {cell }}^{\circ}$, for the battery.

Aadit Sharma

Numerade Educator

Problem 35

Choose the correct answers: In a product-favored chemical reaction, the standard cell potential, $E_{\text {cell }}^{\circ}$, is (greater/less) than zero, and the Gibbs free energy change, $\Delta_{\mathrm{r}} G^{\circ},$ is (greater/less) than zero.

Anthony Han

Numerade Educator

Problem 36

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4},$ can be used as the reducing agent in a fuel cell.
$$
\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+\mathrm{O}_{2}(\mathrm{aq}) \longrightarrow \mathrm{N}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell)
$$
(a) If $\Delta_{t} G^{\circ}$ for the reaction is $-598 \mathrm{~kJ},$ calculate the value of $E^{\circ}$ expected for the reaction.
(b) Suppose the equation is written with all coefficients doubled. Determine $\Delta_{\mathrm{r}} G^{\circ}$ and $E^{\circ}$ for this new reaction.

Anthony Han

Numerade Educator

Problem 37

The standard cell potential for the oxidation of $\mathrm{Mg}$ by
$$
\begin{aligned}
\mathrm{Br}_{2} \text { is } 3.42 \mathrm{~V} \\
& \mathrm{Br}_{2}(\ell)+\mathrm{Mg}(\mathrm{s}) \longrightarrow \mathrm{Mg}^{2+}(\mathrm{aq})+2 \mathrm{Br}^{-}(\mathrm{aq})
\end{aligned}
$$
(a) Calculate $\Delta_{\mathrm{r}} G^{\circ}$ for this reaction.
(b) Suppose the equation is written with all coefficients doubled. Determine $\Delta_{\mathrm{r}} G^{\circ}$ and $E^{\circ}$ for this new equation.

Anthony Han

Numerade Educator

Problem 38

The standard cell potential, $E^{\circ},$ for the reaction of $\mathrm{Zn}(\mathrm{s})$ and $\mathrm{Cl}_{2}(\mathrm{~g})$ is $2.12 \mathrm{~V}$. Write the chemical equation for the reaction of $1 \mathrm{~mol}$ zinc. Calculate the standard Gibbs free energy change, $\Delta_{t} G^{\circ},$ for this reaction.

Aadit Sharma

Numerade Educator

Problem 39

For each of the reactions in Question $31,$ compute the Gibbs free energy change, $\Delta_{t} G^{\circ}$.

Aadit Sharma

Numerade Educator

Problem 40

Calculate the equilibrium constant $K_{\mathrm{c}}$ and $\Delta_{\mathrm{r}} G^{\circ}$ for the reaction between $\mathrm{Cd}(\mathrm{s})$ and $\mathrm{Cu}^{2+}(\mathrm{aq})$.

Anthony Han

Numerade Educator

Problem 41

Calculate the equilibrium constant $K_{\mathrm{c}}$ and $\Delta_{\mathrm{r}} G^{\circ}$ for the reaction between $\mathrm{I}_{2}(\mathrm{~s})$ and $\mathrm{Br}^{-}(\mathrm{aq})$

Anthony Han

Numerade Educator

Problem 42

Calculate the equilibrium constant $K_{\mathrm{c}}$ and $\Delta_{\mathrm{r}} G^{\circ}$ for the reaction between $\mathrm{Ag}(\mathrm{s})$ and $\mathrm{Zn}^{2+}(\mathrm{aq})$

Anthony Han

Numerade Educator

Problem 43

Calculate the equilibrium constant $K_{\mathrm{c}}$ and $\Delta_{\mathrm{r}} G^{\circ}$ for the reaction between $\mathrm{Cl}_{2}(\mathrm{~g})$ and $\mathrm{Br}^{-}(\mathrm{aq})$.

Anthony Han

Numerade Educator

Problem 44

Consider a voltaic cell with the reaction given below. As the cell reaction proceeds, what happens to the values of $E_{\text {cell }}, \Delta_{r} G,$ and $K_{\mathrm{c}} ?$ Explain your answers.
$$
\begin{array}{r}
\mathrm{Cu}^{2+}(\mathrm{aq}, 1 \mathrm{M})+\mathrm{Zn}(\mathrm{s}) \longrightarrow \mathrm{Cu}(\mathrm{s})+\mathrm{Zn}^{2+}(\mathrm{aq}, 1 \mathrm{M}) \\
E_{\mathrm{cell}}^{\circ}=1.10 \mathrm{~V}
\end{array}
$$

Anthony Han

Numerade Educator

Problem 45

Calculate the equilibrium constant $K_{\mathrm{c}}$ for this reaction.
$$
\begin{aligned}
\mathrm{Ni}(\mathrm{s})+\mathrm{Co}^{2+}(\mathrm{aq}) \rightleftharpoons \mathrm{Ni}^{2+}(\mathrm{aq}) &+\mathrm{Co}(\mathrm{s}) \\
E_{\mathrm{cell}}^{\circ}=-0.027 \mathrm{~V}
\end{aligned}
$$

Anthony Han

Numerade Educator

Problem 46

Consider the voltaic cell
$$
\mathrm{Zn}(\mathrm{s})+\mathrm{Cd}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{Zn}^{2+}(\mathrm{aq})+\mathrm{Cd}(\mathrm{s})
$$
operating at $298 \mathrm{~K}$.
(a) Calculate the $E_{\text {cell }}^{\circ}$ for this cell.
(b) If $E_{\text {cell }}=0.390$ and (conc. $\left.\mathrm{Cd}^{2+}\right)=2.00 \mathrm{M},$ calculate the (conc. $\mathrm{Zn}^{2+}$ ).
(c) If (conc. $\left.\mathrm{Cd}^{2+}\right)=0.068 \mathrm{M}$ and $\left(\mathrm{conc} . \mathrm{Zn}^{2+}\right)=1.00 \mathrm{M}$
calculate the $E_{\text {cell }}$.

Anthony Han

Numerade Educator

Problem 47

Consider the voltaic cell
$$
2 \mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{Cd}(\mathrm{s}) \longrightarrow 2 \mathrm{Ag}(\mathrm{s})+\mathrm{Cd}^{2+}(\mathrm{aq})
$$
operating at $298 \mathrm{~K}$.
(a) Calculate the $E_{\text {cell }}^{\circ}$ for this cell.
(b) If (conc. $\left.\mathrm{Cd}^{2+}\right)=2.0 \mathrm{M}$ and $\left(\mathrm{conc} . \mathrm{Ag}^{+}\right)=0.25 \mathrm{M},$ cal-
culate $E_{\text {cell }}$
(c) If $E_{\text {cell }}=1.25 \mathrm{~V}$ and $\left(\mathrm{conc.} \mathrm{Cd}^{2+}\right)=0.100 \mathrm{M},$ calculate
$$
\left(\mathrm{conc} . \mathrm{Ag}^{+}\right)
$$

Anthony Han

Numerade Educator

Problem 48

Consider a voltaic cell with the reaction
$$
\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Sn}^{4+}(\mathrm{aq}) \longrightarrow 2 \mathrm{H}^{+}(\mathrm{aq})+\mathrm{Sn}^{2+}(\mathrm{aq})
$$
operating at $298 \mathrm{~K}$.
(a) Calculate the $E_{\text {cell }}^{\circ}$ for this cell.
(b) Calculate the $E_{\text {cell }}$ for $P_{\mathrm{H}_{2}}=1.0 \mathrm{bar},\left(\right.$ conc. $\left.\mathrm{Sn}^{2+}\right)=$
$$
6.0 \times 10^{-4} \mathrm{M},\left(\text { conc. } \mathrm{Sn}^{4+}\right)=5.0 \times 10^{-4} \mathrm{M}, \text { and }
$$
$\mathrm{pH}=3.60$

Anthony Han

Numerade Educator

Problem 49

Calculate the cell potential of a concentration cell that contains two hydrogen electrodes if the cathode contacts a solution with $\mathrm{pH}=7.8$ and the anode contacts a solution with (conc. $\left.\mathrm{H}^{+}\right)=0.05 \mathrm{M}$.

Anthony Han

Numerade Educator

Problem 50

Calculate the potential of a cell with one electrode made from zinc metal immersed in a solution where (conc. $\left.\mathrm{Zn}^{2+}\right)=0.010 \mathrm{M}$ and the other electrode is a standard hydrogen electrode.

Anthony Han

Numerade Educator

Problem 51

For a voltaic cell with the reaction
$$
\mathrm{Pb}(\mathrm{s})+\mathrm{Sn}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{Pb}^{2+}(\mathrm{aq})+\mathrm{Sn}(\mathrm{s})
$$
calculate the ratio of concentrations of lead and tin ions when $E_{\text {cell }}=0$.

Anthony Han

Numerade Educator

Problem 52

Describe the advantages and disadvantages of lead-acid storage batteries.

Aadit Sharma

Numerade Educator

Problem 53

Describe the advantages and disadvantages of Li-ion batteries.

Aadit Sharma

Numerade Educator

Problem 54

NiCad batteries are rechargeable and are commonly used in cordless appliances. Although such batteries actually function under basic conditions, imagine a voltaic cell using the setup in the diagram shown.

Aadit Sharma

Numerade Educator

Problem 55

Consider the NiCad cell in Question 54 .
(a) If the concentration of $\mathrm{Cd}^{2+}$ is reduced to $0.010 \mathrm{M},$ and (conc. $\left.\mathrm{Ni}^{2+}\right)=1.0 \mathrm{M},$ is $E_{\text {cell }}$ smaller or larger than when the concentration of $\mathrm{Cd}^{2+}$ (aq) was $1.0 \mathrm{M} ?$ Explain your answer in terms of Le Chatelier's principle.
(b) Begin with $1.0 \mathrm{~L}$ of each of the solutions, both initially 1.0 M in dissolved species. Each electrode weighs $50.0 \mathrm{~g}$ at the start. If $0.050 \mathrm{~A}$ is drawn from the battery, calculate how long the battery can operate.

Aadit Sharma

Numerade Educator

Problem 56

How does a fuel cell differ from a battery?

Catherine Lemar

Catherine Lemar

Numerade Educator

Problem 57

Describe the principal parts of an $\mathrm{H}_{2} \mid \mathrm{O}_{2}$ fuel cell. Write a balanced equation for the reaction at the cathode; at the anode. Give the formula of the product of the fuel cell reaction.

Aadit Sharma

Numerade Educator

Problem 58

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$, has been proposed as the fuel in a fuel cell in which oxygen is the oxidizing agent. The reactions are
$$
\begin{array}{r}
\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+4 \mathrm{OH}^{-}(\mathrm{aq}) \longrightarrow \mathrm{N}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(\ell)+4 \mathrm{e}^{-} \\
\mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell)+4 \mathrm{e}^{-} \longrightarrow 4 \mathrm{OH}^{-}(\mathrm{aq})
\end{array}
$$
(a) Which reaction occurs at the anode and which at the cathode?
(b) What is the overall cell reaction?
(c) If the cell is to produce $0.50 \mathrm{~A}$ of current for $50.0 \mathrm{~h}, \mathrm{cal}-$ culate what mass in grams of hydrazine must be present.
(d) Calculate what mass (g) of $\mathrm{O}_{2}$ must be available to react with the mass of $\mathrm{N}_{2} \mathrm{H}_{4}$ determined in part (c).

Aadit Sharma

Numerade Educator

Problem 59

Consider the electrolysis of water in the presence of very dilute $\mathrm{H}_{2} \mathrm{SO}_{4}$. What species is produced at the anode? At the cathode? What are the relative amounts of the species produced at the two electrodes?

Aadit Sharma

Numerade Educator

Problem 60

Write chemical equations for the electrolysis of molten salts of three different alkali halides to produce the corresponding halogens and alkali metals.

Aadit Sharma

Numerade Educator

Problem 61

From Table 17.1 write down all of the aqueous metal ions that can be reduced by electrolysis to the corresponding metal.

Aadit Sharma

Numerade Educator

Problem 62

From Table 17.1 write down all of the aqueous species that can be oxidized by electrolysis, and determine the products.

Aadit Sharma

Numerade Educator

Problem 63

Identify the products of the electrolysis of a 1 -M aqueous solution of NaBr. What species are present in the solution? What is formed at the cathode? What is formed at the anode?

Anthony Han

Numerade Educator

Problem 64

For each of these solutions, tell what reactions take place at the anode and at the cathode during electrolysis.
(a) $\mathrm{NiBr}_{2}(\mathrm{aq})$
(b) $\mathrm{NaI}(\mathrm{aq})$
(c) $\mathrm{CdCl}_{2}(\mathrm{aq})$
(d) $\mathrm{CuI}_{2}(\mathrm{aq})$
(e) $\mathrm{MgF}_{2}(\mathrm{aq})$
(f) $\mathrm{HNO}_{3}(\mathrm{aq})$

Aadit Sharma

Numerade Educator

Problem 65

A current of $0.015 \mathrm{~A}$ is passed through a solution of $\mathrm{AgNO}_{3}$ for 155 min. Calculate the mass of silver deposited at the cathode.

Paul Gabriel

Numerade Educator

Problem 66

A current of $1.0 \mathrm{~mA}$ is passed through a solution containing $\mathrm{Ag}^{+}(\mathrm{aq}) .$ Calculate the mass of silver in the solution if all the silver was deposited as Ag metal in $14.5 \mathrm{~min}$.

Anthony Han

Numerade Educator

Problem 67

A current of $2.50 \mathrm{~A}$ is passed through a solution of $\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}$ for $2.00 \mathrm{~h} .$ Calculate the mass of copper deposited at the cathode.

Anthony Han

Numerade Educator

Problem 68

A current of $0.0125 \mathrm{~A}$ is passed through a solution of $\mathrm{CuCl}_{2}$ for $2.00 \mathrm{~h} .$ Calculate the mass of copper deposited at the cathode and the volume of $\mathrm{Cl}_{2}$ gas (in $\mathrm{mL}$ at STP) produced at the anode.

Anthony Han

Numerade Educator

Problem 69

The major reduction half-reaction occurring in the cell in which molten $\mathrm{Al}_{2} \mathrm{O}_{3}$ and molten aluminum salts are electrolyzed is $\mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s})$. The cell operates
at $5.0 \mathrm{~V}$ and $1.0 \times 10^{5} \mathrm{~A} .$ Calculate the mass $(\mathrm{g})$ of aluminum metal produced in $8.0 \mathrm{~h}$.

Anthony Han

Numerade Educator

Problem 70

The vanadium(II) ion can be produced by electrolysis of a vanadium(III) salt in solution. Calculate how long you must carry out an electrolysis if you wish to convert completely $0.125 \mathrm{~L}$ of $0.0150-\mathrm{M} \mathrm{V}^{3+}(\mathrm{aq})$ to $\mathrm{V}^{2+}(\mathrm{aq})$ using a current of $0.268 \mathrm{~A}$.

Anthony Han

Numerade Educator

Problem 71

The reactions occurring in a lead-acid storage battery are given in Section $17-8$ a. A typical battery might be rated at 50 . ampere-hours (A-h). This means that it has the capacity to deliver 50 . A for $1.0 \mathrm{~h}$ or $1.0 \mathrm{~A}$ for $50 . \mathrm{h}$. If it does deliver $1.0 \mathrm{~A}$ for $50 . \mathrm{h},$ calculate the mass of lead consumed.

Aadit Sharma

Numerade Educator

Problem 72

An effective battery can be built using the reaction between Al metal and $\mathrm{O}_{2}$ from the air. If the $\mathrm{Al}$ anode of this battery consists of a 3 -oz piece of aluminum $(84 \mathrm{~g})$ determine how long (h) the battery can produce $1.0 \mathrm{~A}$ before going dead.

Anthony Han

Numerade Educator

Problem 73

Assume that the anode reaction for the lithium battery is
$$
\mathrm{LiC}_{6}(\mathrm{~s}) \longrightarrow \mathrm{Li}^{+}(\text {electrolyte })+\mathrm{C}_{6}(\mathrm{~s})+\mathrm{e}^{-}
$$
and the anode reaction for the lead-acid storage battery is
$$
\mathrm{Pb}(\mathrm{s})+\mathrm{HSO}_{4}^{-}(\mathrm{aq}) \longrightarrow \mathrm{PbSO}_{4}(\mathrm{~s})+2 \mathrm{e}^{-}+\mathrm{H}^{+}(\mathrm{aq})
$$
Compare the masses of metals consumed when each of these batteries supplies a current of $1.0 \mathrm{~A}$ for $10 . \mathrm{min}$.

Aadit Sharma

Numerade Educator

Problem 74

A hydrogen-oxygen fuel cell operates on the simple reaction
$$
2 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(\ell)
$$
If the cell is designed to produce $1.5 \mathrm{~A}$ of current, determine how long it can operate if there is an excess of oxygen and only sufficient hydrogen to fill a $1.0-\mathrm{L}$ tank at 200. bar pressure at $25^{\circ} \mathrm{C}$.

Anthony Han

Numerade Educator

Problem 75

Calculate how long it would take to electroplate a metal surface with $0.500 \mathrm{~g}$ nickel metal from a solution of $\mathrm{Ni}^{2+}$ with a current of $4.00 \mathrm{~A}$.

Anthony Han

Numerade Educator

Problem 76

Calculate how much current is required to electroplate a metal surface with $0.400 \mathrm{~g}$ chromium metal from a solution of $\mathrm{Cr}^{3+}$ in $1.00 \mathrm{~h}$.

Anthony Han

Numerade Educator

Problem 77

Explain how rust is formed from iron materials by corrosion.

Aadit Sharma

Numerade Educator

Problem 78

Why does iron corrode faster in salt water than in fresh water?

Aadit Sharma

Numerade Educator

Problem 79

Name one common metal that does not corrode readily under normal conditions.

Aadit Sharma

Numerade Educator

Problem 80

Why does coating a steel object with chromium stop corrosion of the iron?

Aadit Sharma

Numerade Educator

Problem 81

Explain how galvanizing iron stops corrosion of the underlying iron.

Aadit Sharma

Numerade Educator

Problem 82

Does $1.0-\mathrm{M}$ nitric acid, $\mathrm{HNO}_{3},$ oxidize metallic gold to form a $1-\mathrm{M} \mathrm{Au}^{3+}$ solution? Explain why or why not.

Aadit Sharma

Numerade Educator

Problem 83

A 12-V automobile battery consists of six cells of the type described in Section $17-8 a$. The cells are connected in series so that the same current flows through all of them. Calculate the theoretical minimum electrical potential difference needed to recharge an automobile battery. (Assume standard-state concentrations.) How does this compare with the maximum voltage that could be delivered by the battery? Assuming that the lead plates in an automobile battery each weigh $2.50 \mathrm{~kg}$ and that sufficient $\mathrm{PbO}_{2}$ is available, calculate the maximum possible work that could be obtained from the battery.

Aadit Sharma

Numerade Educator

Problem 84

Three electrolytic cells are connected in series, so that the same current flows through all of them for $20 .$ min. In cell A, 0.0234 g Ag plates out from a solution of $\mathrm{AgNO}_{3}(\mathrm{aq}) ;$ cell $\mathrm{B}$ contains $\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) ;$ cell $\mathrm{C}$ contains $\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}($ aq $) .$ Calculate what mass of $\mathrm{Cu}$ will plate out in cell B. Calculate what mass of Al will plate out in cell C.

Anthony Han

Numerade Educator

Problem 85

Fluorinated organic compounds are important commercially; they are used as herbicides, flame retardants, and fire-extinguishing agents, among other things. A reaction such as
$$
\mathrm{CH}_{3} \mathrm{SO}_{2} \mathrm{~F}+3 \mathrm{HF} \longrightarrow \mathrm{CF}_{3} \mathrm{SO}_{2} \mathrm{~F}+3 \mathrm{H}_{2}
$$
is actually carried out electrochemically in liquid HF as the solvent.
(a) Draw the structural formula for $\mathrm{CH}_{3} \mathrm{SO}_{2} \mathrm{~F}$. (S is the "central" atom with the $\mathrm{O}$ atoms, $\mathrm{F}$ atom, and $\mathrm{CH}_{3}$ group bonded to it.) What is the geometry around the $\mathrm{S}$ atom? What are the $\mathrm{O}-\mathrm{S}-\mathrm{O}$ and $\mathrm{O}-\mathrm{S}-\mathrm{F}$ bond angles?
(b) If you electrolyze $150 . \mathrm{g} \mathrm{CH}_{3} \mathrm{SO}_{2} \mathrm{~F}$, determine how many grams of $\mathrm{HF}$ are required and how many grams of each product can be isolated.
(c) Is $\mathrm{H}_{2}$ produced at the anode or the cathode of the electrolysis cell?
(d) A typical electrolysis cell operates at $8.0 \mathrm{~V}$ and $250 \mathrm{~A}$. Calculate how many kilowatt-hours of energy one such cell consumes in $24 \mathrm{~h}$.

Aadit Sharma

Numerade Educator

Problem 86

Fluorine, $\mathrm{F}_{2}$, is made by the electrolysis of anhydrous $\mathrm{HF}$.
$$
2 \mathrm{HF}(\ell) \longrightarrow \mathrm{H}_{2}(\mathrm{~g})+\mathrm{F}_{2}(\mathrm{~g})
$$
Typical electrolysis cells operate at 4000 to $6000 \mathrm{~A}$ and 8 to $12 \mathrm{~V}$. A large-scale plant can produce about $9.0 \mathrm{met}-$ ric tons of $\mathrm{F}_{2}$ gas per day.
(a) Calculate the mass (g) of HF consumed.
(b) Using the conversion factor of $3.60 \times 10^{6} \mathrm{~J} / \mathrm{kWh}$, calculate how much energy in kilowatt-hours is transferred to a cell operating at $6.0 \times 10^{3} \mathrm{~A}$ at $12 \mathrm{~V}$ for $24 \mathrm{~h}$.

Aadit Sharma

Numerade Educator

Problem 87

What reaction takes place when a 1.0 -M solution of $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ is added to a 1.0 -M solution of $\mathrm{HBr} ?$

Anthony Han

Numerade Educator

Problem 88

An electric current of 2.00 A was passed through a platinum salt solution for 3.00 hours, and $10.9 \mathrm{~g}$ of metallic platinum was formed at the cathode. Determine the charge on the platinum ions in the solution.

Anthony Han

Numerade Educator

Problem 89

You wish to electroplate a copper surface having an area of $1200 \mathrm{~mm}^{2}$ with a $1.0-\mu \mathrm{m}$ -thick coating of silver from a solution of $\mathrm{Ag}(\mathrm{CN})_{2}^{-}$ ions. If you use a current of $150.0 \mathrm{~mA},$ calculate how much electrolysis time you should use. The density of metallic silver is $10.5 \mathrm{~g} / \mathrm{cm}^{3} .$

Anthony Han

Numerade Educator

Problem 90

In a mercury battery, the anode reaction is
$$
\mathrm{Zn}(\mathrm{s})+2 \mathrm{OH}^{-}(\mathrm{aq}) \longrightarrow \mathrm{ZnO}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)+2 \mathrm{e}^{-}
$$
and the cathode reaction is
$$
\mathrm{HgO}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)+2 \mathrm{e}^{-} \longrightarrow \mathrm{Hg}(\ell)+2 \mathrm{OH}^{-}(\mathrm{aq})
$$
The cell potential is $1.35 \mathrm{~V}$. Calculate how many hours such a battery can provide power at a rate of $4.0 \times 10^{-4}$ watt $\left(1\right.$ watt $\left.=1 \mathrm{~J} \mathrm{~s}^{-1}\right)$ if $1.25 \mathrm{~g} \mathrm{HgO}$ is
available.

Anthony Han

Numerade Educator

Problem 91

Four metals $\mathrm{A}, \mathrm{B}, \mathrm{C},$ and $\mathrm{D}$ exhibit these properties:
(a) Only $\mathrm{A}$ and $\mathrm{C}$ react with $1.0-\mathrm{M} \mathrm{HCl}$ to give $\mathrm{H}_{2}$ gas.
(b) When $\mathrm{C}$ is added to solutions of ions of the other metals, metallic $\mathrm{A}, \mathrm{B},$ and $\mathrm{D}$ are formed.
(c) Metal D reduces $\mathrm{B}^{n+}$ ions to give metallic $\mathrm{B}$ and $\mathrm{D}^{n+}$ ions. On the basis of this information, arrange the four metals in order of increasing ability to act as reducing agents.

Aadit Sharma

Numerade Educator

Problem 92

The table below lists the cell potentials for the ten possible voltaic cells assembled from the elements $\mathrm{A}, \mathrm{B}, \mathrm{C}, \mathrm{D}$ and $\mathrm{E}$ and their respective ions in solutions. Using the data in the table, establish a standard half-cell potential table similar to Table 17.1. Assign a half-cell potential of $0.00 \mathrm{~V}$ to the element that falls in the middle of the series.
$$
\begin{array}{lcc}
\hline & \mathrm{A}(\mathrm{s}) \text { in } \mathrm{A}^{n+}(\mathrm{aq}) & \mathrm{B}(\mathrm{s}) \text { in } \mathrm{B}^{n+}(\mathrm{aq}) \\
\hline \mathrm{E}(\mathrm{s}) \text { in } \mathrm{E}^{n+}(\mathrm{aq}) & +0.21 \mathrm{~V} & +0.68 \mathrm{~V} \\
\mathrm{D}(\mathrm{s}) \text { in } \mathrm{D}^{n+}(\mathrm{aq}) & +0.35 \mathrm{~V} & +1.24 \mathrm{~V} \\
\mathrm{C}(\mathrm{s}) \text { in } \mathrm{C}^{n+}(\text { aq }) & +0.58 \mathrm{~V} & +0.31 \mathrm{~V} \\
\mathrm{~B}(\mathrm{~s}) \text { in } \mathrm{B}^{n+}(\text { aq }) & +0.89 \mathrm{~V} & - \\
\hline & \mathrm{C}(\mathrm{s}) \text { in } \mathrm{C}^{n+}(\mathrm{aq}) & \mathrm{D}(\mathrm{s}) \text { in } \mathrm{D}^{n+}(\mathrm{aq}) \\
\hline \mathrm{E}(\mathrm{s}) \text { in } \mathrm{E}^{n+}(\mathrm{aq}) & +0.37 \mathrm{~V} & +0.56 \mathrm{~V} \\
\mathrm{D}(\mathrm{s}) \text { in } \mathrm{D}^{n+}(\mathrm{aq}) & +0.93 \mathrm{~V} & - \\
\mathrm{C}(\mathrm{s}) \text { in } \mathrm{C}^{n+}(\mathrm{aq}) & - & - \\
\mathrm{B}(\mathrm{s}) \text { in } \mathrm{B}^{n+}(\mathrm{aq}) & - & - \\
\hline
\end{array}
$$

Aadit Sharma

Numerade Educator

Problem 93

When the voltaic cell shown here runs for several hours, the green solution gets lighter and the yellow solution gets darker.
(a) Determine what is oxidized and what is reduced.
(b) Identify the oxidizing agent and the reducing agent.
(c) Identify the anode and the cathode.
(d) Write equations for the half-reactions.
(e) Which metal electrode gains mass?
(f) What is the direction of the electron transfer through the external wire?
(g) If the salt bridge contains $\mathrm{KNO}_{3}(\mathrm{aq})$, into which solution will the $\mathrm{K}^{+}$ ions migrate?

David Collins

Numerade Educator

Problem 94

An electrolytic cell is set up with $\mathrm{Cd}(\mathrm{s})$ in $\mathrm{Cd}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$
and $\mathrm{Zn}(\mathrm{s})$ in $\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) .$ Initially both electrodes weigh $5.00 \mathrm{~g}$. After running the cell for several hours the electrode in the left compartment weighs $4.75 \mathrm{~g}$.
(a) Which electrode is in the left compartment?
(b) Does the mass of the electrode in the right compartment increase, decrease, or stay the same? If the mass changes, what is the new mass?
(c) Does the volume of the electrode in the right compartment increase, decrease, or stay the same? If the volume changes, what is the new volume? (The density of $\mathrm{Cd}$ is $\left.8.65 \mathrm{~g} / \mathrm{cm}^{3} .\right)$

Aadit Sharma

Numerade Educator

Problem 95

Using data from Appendix I, show why
(a) $\mathrm{Co}^{3+}$ is not stable in aqueous solution.
(b) $\mathrm{Fe}^{2+}$ is not stable in air.

Aadit Sharma

Numerade Educator

Problem 96

When $\mathrm{H}_{2} \mathrm{O}_{2}$ is mixed with $\mathrm{Fe}^{2+},$ which redox reaction occurs - the oxidation of $\mathrm{Fe}^{2+}$ to $\mathrm{Fe}^{3+}$ or the reduction of $\mathrm{Fe}^{2+}$ to Fe? Determine what the $E_{\text {cell }}^{\circ}$ values are for the voltaic cells corresponding to the two reactions.

Aadit Sharma

Numerade Educator

Problem 97

The permanganate ion $\mathrm{MnO}_{4}^{-}$ can be reduced to the manganese(II) ion $\mathrm{Mn}^{2+}$ in aqueous acidic solution, and the half-cell potential for this half-cell reaction is $1.51 \mathrm{~V}$. If this half-cell is combined with a $\mathrm{Zn}^{2+} \mid \mathrm{Zn}$ half-cell to form a voltaic cell at standard conditions,
(a) Write the chemical equation for the half-reaction occurring at the anode.
(b) Write the chemical equation for the half-reaction occurring at the cathode.
(c) Write the overall balanced equation for the reaction.
(d) Calculate the cell potential.

Anthony Han

Numerade Educator

Problem 98

Consider two different electrolytic cells; one cell contains aqueous $\mathrm{Zn}^{2+}$ and the other contains $\mathrm{Cr}^{3+}$. The initial metal ion concentration is the same in each cell and the metal ions are reduced to the metal during the electrolysis. Each cell operates at the same current. Without doing calculations, predict which cell has the greater mass of metal deposited after 5 min. Explain your prediction.

Aadit Sharma

Numerade Educator

Problem 99

The $K_{\mathrm{sp}}$ of $\mathrm{Cu}\left(\mathrm{IO}_{3}\right)_{2}$ is $1.4 \times 10^{-7} .$ Calculate the $E^{\circ}$ for $\mathrm{Cu}\left(\mathrm{IO}_{3}\right)_{2}(\mathrm{~s})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Cu}(\mathrm{s})+2 \mathrm{IO}_{3}^{-}(\mathrm{aq})$

Anthony Han

Numerade Educator

Problem 100

Use calculations to determine whether (a) oxygen in air can oxidize silver metal in acidic solution; and (b) oxygen in air can oxidize silver metal in basic solution. In each case, write the balanced cell reaction equation and calculate the standard electrical potential.

Aadit Sharma

Numerade Educator

Problem 101

To measure the $\mathrm{Ag}^{+}$ concentration, $25.00 \mathrm{~mL}$ of a silvercontaining solution is titrated with $0.015 \mathrm{M} \mathrm{KI}$ at $25^{\circ} \mathrm{C}$ by using a silver electrode immersed in the test solution and the electrical potential measured against a standard hydrogen electrode. It required $16.7 \mathrm{~mL}$ of the KI solution to reach the equivalence point, where the potential was $0.325 \mathrm{~V}$.
(a) Calculate the molarity of $\mathrm{Ag}^{+}$ in the solution.
(b) Calculate the $K_{\mathrm{sp}}$ of $\mathrm{AgI}$.

David Collins

Numerade Educator

Problem 102

The $\mathrm{K}^{+}$ concentration inside a nerve cell differs from that outside the cell. Calculate the difference in electrical potential required for the $\mathrm{K}^{+}$ concentration inside a nerve cell to be 45 times greater than that outside the cell. Assume that the potential difference is due only to the $\mathrm{K}^{+}$ concentration difference.

Anthony Han

Numerade Educator

Problem 103

A pH meter is standardized using a pH 9.40 buffer; the cell potential is $+0.060 \mathrm{~V}$. When the buffer is replaced with a solution of unknown $\mathrm{H}^{+}(\mathrm{aq})$ concentration, the cell potential is $+0.22 \mathrm{~V}$. Calculate the $\mathrm{pH}$ of the test solution.

Aadit Sharma

Numerade Educator

Problem 104

Consider these unbalanced equations for two reactions:
$\mathrm{NO}_{3}^{-}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq})+\mathrm{Hg}(\ell) \longrightarrow \underset{\mathrm{Hg}_{2}^{2+}}(\mathrm{aq})+\mathrm{NO}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell)$
$$
\mathrm{Hg}^{2+}(\mathrm{aq})+\mathrm{Br}^{-}(\mathrm{aq}) \longrightarrow \mathrm{Hg}_{2}^{2+}(\mathrm{aq})+\mathrm{Br}_{2}(\ell)
$$
For each reaction:
(a) balance the equation.
(b) draw a cell diagram.
(c) calculate the standard cell potential.
(d) calculate the $\Delta_{t} G^{\circ} .$
(e) determine whether each reaction is product-favored. Explain your reason.

David Collins

Numerade Educator

Problem 105

The standard potential of a $\mathrm{Zn}\left|\mathrm{Zn}^{2+} \| \mathrm{Cu}^{2+}\right| \mathrm{Cu}$ voltaic cell is $1.103 \mathrm{~V}$. As the cell operates, the cell potential changes due to concentration changes of $\mathrm{Zn}^{2+}$ and $\mathrm{Cu}^{2+} .$ Calculate the ratio (conc. $\left.\mathrm{Zn}^{2+}\right) /\left(\right.$ conc. $\left.\mathrm{Cu}^{2+}\right)$ when the cell potential is $0.050 \mathrm{~V}$.

Anthony Han

Numerade Educator

Problem 106

In an electrolytic cell, a 10.0 -A direct current passes through an aqueous copper(II) nitrate solution and $9.50 \mathrm{~g}$ metallic copper plates out.
(a) Calculate how long it took for this mass of copper to be deposited at the cathode. Assume $100 \%$ efficiency.
(b) A gas is produced at the anode and collected. Identify the gas and calculate its volume. The gas was collected at $25^{\circ} \mathrm{C}$ and $0.945 \mathrm{~atm} .$

Anthony Han

Numerade Educator

Problem 107

Consider a voltaic cell to study the reaction of chromium and zinc. The cell consists of the usual array of a salt bridge, appropriate wiring, and two half-cells: (1) a chromium metal electrode dipping into an aqueous solution of $\mathrm{Cr}^{2+}$ ions; and (2) a zinc metal electrode dipping into an aqueous solution of $\mathrm{Zn}^{2+}$ ions.
(a) Calculate the cell potential at standard conditions.
(b) Calculate $\Delta_{\mathrm{r}} G_{\text {cell }}^{\circ}$
(c) The concentration of metal ions is changed to
$$
\begin{array}{l}
\mathrm{Cr}^{2+}=0.050 \mathrm{M} \text { and } \mathrm{Zn}^{2+}=0.010 \mathrm{M} \text { . Calculate } \\
\Delta_{\mathrm{r}} G_{\mathrm{cell}} \text { and } E_{\mathrm{cell}} \text { . }
\end{array}
$$

David Collins

Numerade Educator

Problem 108

If $\mathrm{Cl}_{2}$ and $\mathrm{Br}_{2}$ are added to an aqueous solution that contains $\mathrm{Cl}^{-}$ and $\mathrm{Br}^{-},$ what product-favored reaction will occur?

Anthony Han

Numerade Educator

Problem 109

This reaction occurs in a cell with $\mathrm{H}_{2}(\mathrm{~g})$ pressure of $1.0 \mathrm{~atm}$ and (conc. $\left.\mathrm{Cl}^{-}\right)=1.0 \mathrm{M}$ at $25^{\circ} \mathrm{C} ;$ the measured
$E_{\text {cell }}=0.34 \mathrm{~V}$. Calculate the $\mathrm{pH}$ of the solution.
$$
\mathrm{H}_{2}(\mathrm{~g})+2 \mathrm{AgCl}(\mathrm{s}) \longrightarrow 2 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})
$$

Anthony Han

Numerade Educator

Problem 110

$E_{\text {cell }}=0.013 \mathrm{~V}$ for a voltaic cell with this reaction at $25^{\circ} \mathrm{C}$.
$$
\mathrm{Sn}(\mathrm{s})+\mathrm{Pb}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{Sn}^{2+}(\mathrm{aq})+\mathrm{Pb}(\mathrm{s})
$$
(a) Calculate the equilibrium constant $K_{\mathrm{c}}$ for the reaction.
(b) If a solution with (conc. $\left.\mathrm{Pb}^{2+}\right)=1.1 \mathrm{M}$ had excess tin metal added to it, calculate the equilibrium concentrations of $\mathrm{Sn}^{2+}$ and $\mathrm{Pb}^{2+}$.

Anthony Han

Numerade Educator

Problem 111

A student wanted to measure the copper(II) concentration in aqueous solution. For the cathode half-cell she used a silver electrode with a 1.00 -M solution of $\mathrm{AgNO}_{3}$. For the anode half-cell she used a copper electrode dipped into the aqueous sample. The cell gave $E_{\text {cell }}=$ $0.62 \mathrm{~V}$ at $25^{\circ} \mathrm{C}$. Calculate the copper(II) ion concentration of the solution.

Anthony Han

Numerade Educator