Chemistry: The Molecular Science

John W. Moore, Conrad L. Stanitski, Peter C. Jurs

Chapter 19

Electrochemistry and Its Applications - all with Video Answers

Educators

Chapter Questions

Problem 1

Describe the principal parts of an electrochemical cell by drawing a hypothetical cell, indicating the cathode, the anode, the direction of electron flow outside the cell, and the direction of ion flow within the cell.

Nicole Mabante

Nicole Mabante

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.

Nicole Mabante

Numerade Educator

Problem 5

Tell whether each of these statements is true or false. If false, rewrite it to make it a correct statement.
(a) Oxidation always occurs at the anode of an electrochemical cell.
(b) The anode of a voltaic cell is the site of reduction and is negative.
(c) Standard 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 voltage $E_{\text {cell }}^{\circ}$, with a negative sign.

Nicole Mabante

Numerade Educator

Problem 6

In each of these reactions assign oxidation numbers to all species, and tell which substance is oxidized and which is reduced. Tell which is the oxidizing agent and which is the reducing agent. (a) $2 \mathrm{Al}(\mathrm{s})+3 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{AlCl}_{3}(\mathrm{~s})$
(b) $8 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq})+5 \mathrm{Fe}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{Fe}^{3+}(\mathrm{aq})+\mathrm{Mn}^{2+}(\mathrm{aq})+12 \mathrm{H}_{2} \mathrm{O}(\ell)$
(c) $\mathrm{FeS}(\mathrm{s})+3 \mathrm{NO}_{3}^{-}(\mathrm{aq})+4 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \longrightarrow$
$3 \mathrm{NO}(\mathrm{g})+\mathrm{SO}_{4}^{2-}(\mathrm{aq})+\mathrm{Fe}^{3+}(\mathrm{aq})+6 \mathrm{H}_{2} \mathrm{O}(\ell)$

Nicole Mabante

Numerade Educator

Problem 7

In each of these reactions assign oxidation numbers to all species, and tell which substance is oxidized and which is reduced. Tell which is the oxidizing agent and which is the reducing agent.
(a) $\mathrm{Fe}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow \mathrm{FeBr}_{2}(\mathrm{~s})$
(b) $8 \mathrm{HI}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow$
$\mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})+4 \mathrm{I}_{2}(\mathrm{~s})+4 \mathrm{H}_{2} \mathrm{O}(\ell)$
(c) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+2 \mathrm{Fe}^{2+}(\mathrm{aq})+2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \longrightarrow$

Nicole Mabante

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.

Nicole Mabante

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 zinc to $\mathrm{Zn}^{2+}$ ions
(b) Reduction of $\mathrm{H}_{3} \mathrm{O}^{+}$ ions to hydrogen gas
(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

Nicole Mabante

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 hydrogen gas to $\mathrm{H}_{3} \mathrm{O}^{+}$ ions
(d) Reduction of hydrogen peroxide to water in acidic solution
(e) Oxidation of nitric oxide to nitrogen monoxide in acidic solution

Nicole Mabante

Numerade Educator

Problem 12

For each reaction in Question 6 , write balanced halfreactions.

Nicole Mabante

Numerade Educator

Problem 13

For each reaction in Question 7 , write balanced halfreactions.

Nicole Mabante

Numerade Educator

Problem 14

Balance this redox reaction in a basic solution:
$$
\mathrm{Zn}(\mathrm{s})+\mathrm{NO}_{3}^{-}(\mathrm{aq}) \longrightarrow\left[\mathrm{Zn}(\mathrm{OH})_{4}\right]^{2-}(\mathrm{aq})+\mathrm{NH}_{3}(\mathrm{aq})
$$

Nicole Mabante

Numerade Educator

Problem 15

Balance this redox reaction in a basic solution:
$$
\mathrm{NO}_{2}^{-}(\mathrm{aq})+\mathrm{Al}(\mathrm{s}) \longrightarrow \mathrm{NH}_{3}(\mathrm{aq})+\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}(\mathrm{aq})
$$

Nicole Mabante

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) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+\mathrm{Ti}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{Ti}^{4+}(\mathrm{aq})$ 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) $\mathrm{Zn}(\mathrm{Hg})($ amalgam $)+\mathrm{HgO}(\mathrm{s}) \longrightarrow \mathrm{ZnO}(\mathrm{s})+\mathrm{Hg}(\ell)$ in
basic solution

Nicole Mabante

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) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+\mathrm{Co}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{Co}^{3+}(\mathrm{aq}) \mathrm{in}$
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) $\mathrm{CuFeS}_{2}(\mathrm{~s})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{Cu}_{2} \mathrm{~S}(\mathrm{~s})+\mathrm{FeO}(\mathrm{s})+\mathrm{SO}_{2}(\mathrm{~g})$
(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) $\mathrm{C}_{3} \mathrm{H}_{8}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell)$ in acidic
solution

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 $\mathrm{ZnCl}_{2}(\mathrm{aq}) ?$

Nicole Mabante

Numerade Educator

Problem 19

Explain the function of a salt bridge in an electrochemical cell.

Nicole Mabante

Numerade Educator

Problem 20

Are standard half-cell reactions always written as oxidation reactions or reduction reactions? Explain.

Nicole Mabante

Numerade Educator

Problem 21

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 $\mathrm{Li}^{+}+\mathrm{e}^{-} \longrightarrow \mathrm{L}$ is different from that for $2 \mathrm{Li}^{+}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{~L} \mathrm{i}$.

Nicole Mabante

Numerade Educator

Problem 22

A voltaic cell is assembled with $\mathrm{Pb}(\mathrm{s})$ and $\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})$ in one compartment and $\mathrm{Zn}(\mathrm{s})$ and $\mathrm{ZnCl}_{2}(\mathrm{aq})$ in the other. An external wire connects the two electrodes, and a salt bridge containing $\mathrm{KNO}_{3}(\mathrm{aq})$ connects the two solutions.
(a) In the product-favored reaction, zinc metal is oxidized to $\mathrm{Zn}^{2+}$. 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 flow outside the cell and of ion flow within the cell.

Nicole Mabante

Numerade Educator

Problem 23

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 $\mathrm{KNO}_{3}(\mathrm{aq})$ connects the two solutions.
(a) In the product-favored reaction, $\mathrm{Ag}^{+}$ is reduced to silyer 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 flow outside the cell and of ion flow within the cell.

Nicole Mabante

Numerade Educator

Problem 24

You light a $25-\mathrm{W}$ light bulb with the current from a $12 \cdot \mathrm{V}$ lead-acid storage battery. After $1.0 \mathrm{~h}$ of operation, how much energy has the light bulb utilized? How many coulombs have passed through the bulb? Assume $100 \%$ efficiency. (A watt is the transfer of $1 \mathrm{~J}$ of energy in $1 \mathrm{~s}$.)

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Numerade Educator

Problem 25

Draw a diagram of a standard hydrogen electrode and describe how it works.

Nicole Mabante

Numerade Educator

Problem 26

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 27

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 halfreaction and which is the reduction half-reaction.

Nicole Mabante

Numerade Educator

Problem 28

What is the strongest oxidizing agent in Table $19.1$ or Appendix I? What is the strongest reducing agent? What is the weakest oxidizing agent? What is the weakest reducing agent?

Nicole Mabante

Numerade Educator

Problem 29

Using the standard reduction potentials in Table $19.1$, place these elements in order of increasing ability to function as reducing agents:
(a) $\mathrm{Cl}_{2}$
(b) $\mathrm{Fe}$
(c) $\overline{\mathrm{Ag}}$
(d) Na
(e) $\mathrm{H}_{2}$

Nicole Mabante

Numerade Educator

Problem 30

Using the standard reduction potentials in Table $19.1$, 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) $\mathrm{H}_{2} \mathrm{O}$

Nicole Mabante

Numerade Educator

Problem 31

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) According to data from Table $19.1$, what is $E_{\text {cen }}^{\circ}$ for this reaction?

Nicole Mabante

Numerade Educator

Problem 32

Calculate the value of $E_{\mathrm{cell}}^{0}$ 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) $2 \mathrm{Zn}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow$
$2 \mathrm{Zn}^{2+}(\mathrm{aq})+4 \mathrm{OH}^{-}(\mathrm{aq})$

Nicole Mabante

Numerade Educator

Problem 33

Consider these half-reactions:
$$
\begin{array}{lc}
\hline \text { Half-Reaction } & \boldsymbol{E}^{\circ}(\mathrm{V}) \\
\hline \mathrm{Au}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Au}(\mathrm{s}) & 1.52 \\
\mathrm{Pt}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pt}(\mathrm{s}) & 1.118 \\
\mathrm{Co}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Co}(\mathrm{s}) & -0.277 \\
\mathrm{Mn}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Mn}(\mathrm{s}) & -1.18 \\
\hline
\end{array}
$$
(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 Co(s) reduce $\mathrm{Pt}^{2+}(\mathrm{aq})$ to $\mathrm{Pt}(\mathrm{s}) ?$
(f) Will $\mathrm{Pt}(\mathrm{s})$ reduce $\mathrm{Co}^{2+}$ (aq) to $\mathrm{Co}(\mathrm{s}) ?$
(g) Which ions can be reduced by Co(s)?

Nicole Mabante

Numerade Educator

Problem 34

Consider these half-reactions:
$$
\begin{array}{lr}
\hline \text { Half-Reaction } & \boldsymbol{E}^{\circ}(\mathrm{V}) \\
\hline \mathrm{Ce}^{4+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \mathrm{Ce}^{3+}(\mathrm{aq}) & 1.72 \\
\mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \mathrm{Ag}(\mathrm{s}) & 0.80 \\
\mathrm{Hg}_{2}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Hg}(\ell) & 0.80 \\
\mathrm{Sn}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Sn}(\mathrm{s}) & -0.14 \\
\mathrm{Ni}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Ni}(\mathrm{s}) & -0.25 \\
\mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s}) & -1.68 \\
\hline
\end{array}
$$
(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 Sn(s) reduce $\mathrm{Ag}^{+}$ (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 $\mathrm{Ag}^{+}(\mathrm{aq})$ ?

Nicole Mabante

Numerade Educator

Problem 35

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 $\mathrm{Al}^{3+}(\mathrm{aq}) / \mathrm{Al}(\mathrm{s})$ and $\mathrm{Cl}_{2}(\mathrm{~g}) / \mathrm{Cl}^{-}$ (aq) half-reactions.
(b) Tell which half-reaction occurs at the anode and which at the cathode. What are the polarities of these electrodes?
(c) Calculate the standard potential, $E_{c e 1}^{o}$, for the battery.

Nicole Mabante

Numerade Educator

Problem 36

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

Nicole Mabante

Numerade Educator

Problem 37

For each of the reactions in Question 32 , compute the Gibbs free energy change, $\Delta G^{\circ}$.

Nicole Mabante

Numerade Educator

Problem 38

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 $\Delta G^{\circ}$ 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 $\Delta G^{\circ}$ and $E^{\circ}$ for this new reaction.

Nicole Mabante

Numerade Educator

Problem 39

The standard cell potential for the oxidation of $\mathrm{Mg}$ by $\mathrm{Br}_{2}$ is $3.45 \mathrm{~V}$
$$
\mathrm{Br}_{2}(\ell)+\mathrm{Mg}(\mathrm{s}) \longrightarrow \mathrm{Mg}^{2+}(\mathrm{aq})+2 \mathrm{Br}^{-}(\mathrm{aq})
$$
(a) Calculate $\Delta G^{\circ}$ for this reaction.
(b) Suppose the equation is written with all coefficients doubled. Determine $\Delta G^{\circ}$ and $E^{\circ}$ for this new reaction.

Nicole Mabante

Numerade Educator

Problem 40

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, $\Delta G^{\circ}$, for this reaction.

Nicole Mabante

Numerade Educator

Problem 41

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

Nicole Mabante

Numerade Educator

Problem 42

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

Nicole Mabante

Numerade Educator

Problem 43

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

Nicole Mabante

Numerade Educator

Problem 44

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

Nicole Mabante

Numerade Educator

Problem 45

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

Aadit Sharma

Numerade Educator

Problem 46

Estimate the equilibrium constant $K_{c}$ for this reaction.
$$
\begin{aligned}
\mathrm{Ni}(\mathrm{s})+\mathrm{Co}^{2+}(\mathrm{aq}) \rightleftharpoons \mathrm{Ni}^{2+}(\mathrm{aq})+\mathrm{Co}(\mathrm{s}) \\
& E_{\mathrm{cell}}^{\circ}=+0.046 \mathrm{~V}
\end{aligned}
$$

Nicole Mabante

Numerade Educator

Problem 47

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 $E_{\mathrm{cell}}^{\circ}$ for this cell.
(b) If $E_{\text {cell }}=0.390$ and (conc. $\mathrm{Cd}^{2+}$ ) $=2.00 \mathrm{M}$, what is $\left(\right.$ conc. $\left.7 n^{2+}\right) ?$
(c) If (conc. $\left.\mathrm{Cd}^{2+}\right)=0.068 \mathrm{M}$ and $\left(\right.$ conc. $\left.\mathrm{Zn}^{2+}\right)=1.00 \mathrm{M}$, what is $E_{\text {cell? }}$ ?

Nicole Mabante

Numerade Educator

Problem 48

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 $E_{\mathrm{cdl}}^{\circ}$ for this cell.
(b) If (conc. $\left.\mathrm{Cd}^{2+}\right)=2.0 \mathrm{M}$ and $\left(\right.$ conc. $\left.\mathrm{Ag}^{+}\right)=0.25 \mathrm{M}$, what is $E_{\text {cell }} ?$
(c) If $E_{\text {cell }}=1.25 \mathrm{~V}$ and (conc. $\left.\mathrm{Cd}^{2+}\right)=0.100 \mathrm{M}$, what is $\left(\right.$ conc. $\left.\mathrm{Ag}^{+}\right)$ ?

Nicole Mabante

Numerade Educator

Problem 49

Consider the reaction $2 \mathrm{H}_{2} \mathrm{O}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Sn}^{4+}(\mathrm{aq}) \longrightarrow 2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{Sn}^{2+}(\mathrm{aq})$
operating at $298 \mathrm{~K}$.
(a) Calculate the $E_{\text {cell }}^{\circ}$ for this cell.
(b) Calculate the $E_{\text {cell }}$ for $P_{\mathrm{H}_{2}}=1.0 \mathrm{bar},\left(\mathrm{conc} . \mathrm{Sn}^{2+}\right)=$
$6.0 \times 10^{-4} \mathrm{M},\left(\right.$ conc. $\left.\mathrm{Sn}^{4+}\right)=5.0 \times 10^{-4} \mathrm{M}$, and
$\mathrm{pH}=3.60$.

Aadit Sharma

Numerade Educator

Problem 50

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. $\left.\mathrm{H}_{3} \mathrm{O}^{+}\right)=0.05 \mathrm{M}$.

Aadit Sharma

Numerade Educator

Problem 51

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 52

For a voltaic cell with the reaction
$$
\mathrm{Pb}(\mathrm{s})+\mathrm{Sn}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{Pb}^{2+}(\mathrm{aq})+\mathrm{Sn}(\mathrm{s})
$$
at what ratio of concentrations of lead and tin ions will $\boldsymbol{E}_{\text {cell }}=0 ?$

Aadit Sharma

Numerade Educator

Problem 53

What are the advantages and disadvantages of lead-acid storage 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 an electrochemical cell using this setup.
(a) Write a balanced net ionic equation depicting the reaction occurring in the cell.
(b) What is oxidized? What is reduced? What is the reducing agent and what is the oxidizing agent?
(c) Which is the anode and which is the cathode?
(d) Calculate $E^{\circ}$ for the cell.
(e) What is the direction of electron flow in the external wire?
(f) If the salt bridge contains $\mathrm{KNO}_{3}$, toward which compartment will the $\mathrm{NO}_{3}^{-}$ ions migrate?

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. $\left.\mathrm{Ni}^{2+}\right)=1.0 \mathrm{M}$, will the cell emf be smaller or larger than when the concentration of $\mathrm{Cd}^{2+}(\mathrm{aq})$ 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 will 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 $\mathrm{H}_{2} / \mathrm{O}_{2}$ fuel cell. What is the reaction at the cathode? At the anode? What is 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
$\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+4 \mathrm{OH}^{-}(\mathrm{aq}) \longrightarrow \mathrm{N}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(\ell)+4 \mathrm{e}^{-}$
$\mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell)+4 \mathrm{e}^{-} \longrightarrow 4 \mathrm{OH}^{-}(\mathrm{aq})$
(a) Which reaction occurs at the anode and which at the cathode?
(b) What is the net cell reaction?
(c) If the cell is to produce $0.50 \mathrm{~A}$ of current for $50.0 \mathrm{~h}$, what mass in grams of hydrazine must be present?
(d) What mass in grams 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 $19.1$ write down all of the aqueous metal ions that can be reduced by electrolysis to the corresponding metal.

Nicole Mabante

Numerade Educator

Problem 62

From Table $19.1$ write down all of the aqueous species that can be oxidized by electrolysis, and determine the products.

Aadit Sharma

Numerade Educator

Problem 63

What are the products of the electrolysis of a $1-\mathrm{M}$ aqueous solution of NaBr? What species are present in the solution? What is formed at the cathode? What is formed at the anode?

David Collins

Numerade Educator

Problem 64

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

David Collins

Numerade Educator

Problem 65

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

Aadit Sharma

Numerade Educator

Problem 66

Current is passed through a solution containing $\mathrm{Ag}^{+}$ (aq). How much silver was in the solution if all the silver was removed as Ag metal by electrolysis for $14.5 \mathrm{~min}$ at a current of $1.0 \mathrm{~mA}$ ?

Aadit Sharma

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 $2.00 \mathrm{~h}$. What mass of copper is deposited at the cathode?

Aadit Sharma

Numerade Educator

Problem 68

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

Aadit Sharma

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 $\mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \rightarrow \mathrm{Al}(\mathrm{s}) .$ If the cell operates at
$5.0 \mathrm{~V}$ and $1.0 \times 10^{5} \mathrm{~A}$, what mass (in grams) of aluminum metal can be produced in $8.0 \mathrm{~h} ?$

Aadit Sharma

Numerade Educator

Problem 70

The vanadium(II) ion can be produced by electrolysis of a vanadium(III) salt in solution. How long must you 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 $\mathrm{V}^{2+}$ (aq) using a current of $0.268 \mathrm{~A} ?$

Aadit Sharma

Numerade Educator

Problem 71

The reactions occurring in a lead-acid storage battery are given in Section $19.9 .$ 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 $50 . \mathrm{h}$, what mass of lead would be consumed?

Aadit Sharma

Numerade Educator

Problem 72

An effective battery can be built using the reaction between $\mathrm{Al}$ metal and $\mathrm{O}_{2}$ from the air. If the $\mathrm{Al}$ anode of this battery consists of a $3-\mathrm{oz}$ piece of aluminum $(84 \mathrm{~g})$, for how many hours can the battery produce $1.0 \mathrm{~A}$ of electricity?

Aadit Sharma

Numerade Educator

Problem 73

A dry cell is used to supply a current of $250 . \mathrm{mA}$ for $20 \mathrm{~min}$. What mass of $\mathrm{Zn}$ is consumed?

Aadit Sharma

Numerade Educator

Problem 74

If the same current as in Question 73 were supplied by a mercury battery, what mass of Hg would be produced at the cathode?

Aadit Sharma

Numerade Educator

Problem 75

Assume that the anode reaction for the lithium battery is
$$
\mathrm{Li}(\mathrm{s}) \longrightarrow \mathrm{Li}^{+}(\mathrm{aq})+\mathrm{e}^{-}
$$
and the anode reaction for the lead-acid storage battery is
$$
\mathrm{Pb}(\mathrm{s})+\mathrm{HSO}_{4}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{PbSO}_{4}(\mathrm{~s})+2 \mathrm{e}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})
$$
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 76

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, how long can it operate if there is an excess of oxygen and only sufficient hydrogen to fill a 1.0-L tank at 200 . bar pressure at $25^{\circ} \mathrm{C}$ ?

David Collins

Numerade Educator

Problem 77

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

Aadit Sharma

Numerade Educator

Problem 78

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

Aadit Sharma

Numerade Educator

Problem 79

Explain how rust is formed from iron materials by corrosion.

Nicole Mabante

Numerade Educator

Problem 80

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

Nicole Mabante

Numerade Educator

Problem 81

What common metal does not corrode readily under normal conditions?

Aadit Sharma

Numerade Educator

Problem 82

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

Nicole Mabante

Numerade Educator

Problem 83

Explain how galvanizing iron stops corrosion of the underlying iron.

Nicole Mabante

Numerade Educator

Problem 84

A $12-V$ automobile battery consists of six cells of the type described in Section $19.9 .$ 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, what is the maximum possible work that could be obtained from the battery?

David Collins

Numerade Educator

Problem 85

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

Aadit Sharma

Numerade Educator

Problem 86

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 $\mathrm{CH}_{3} \mathrm{SO}_{2} \mathrm{~F} .(\mathrm{S}$ 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 S atom? What are the $\mathrm{O}-\mathrm{S}-\mathrm{O}$ and $\mathrm{O}-\mathrm{S}-\mathrm{F}$ bond angles?
(b) If you electrolyze $150 . \mathrm{g} \mathrm{CH}_{3} \mathrm{SO}_{2} \mathrm{~F}$, how many grams of 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 $250 \mathrm{~A}$. How many kilowatt-hours of energy does one such cell consume in $24 \mathrm{~h} ?$

David Collins

Numerade Educator

Problem 87

Four metals $A, B, C$, and $D$ exhibit these properties:
(a) Only $A$ and $C$ react with $1.0-\mathrm{M} H C l$ to give $H_{2}$ gas.
(b) When $\mathrm{C}$ is added to solutions of ions of the other metals, metallic $\mathbf{A}, \mathbf{B}$, 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.

David Collins

Numerade Educator

Problem 88

The table below lists the cell potentials for the ten possible electrochemical cells assembled from the elements $\bar{A}$, $\mathrm{B}, \mathrm{C}, \mathrm{D}$, and $\mathrm{E}$ and their respective ions in solutions. Using the data in the table, establish a standard reduction potential table similar to Table $19.1 .$ Assign a reduction potential of $0.00 \mathrm{~V}$ to the element that falls in the middle of the series.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 89

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

Nicole Mabante

Numerade Educator

Problem 90

An electrolytic cell is set up with $\mathrm{Cd}(\mathrm{s})$ in $\mathrm{Cd}\left(\mathrm{NO}_{3}\right)_{2}$ (aq) and $\mathrm{Zn}(\mathrm{s})$ in $\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) .$ Initially both electrodes weigh 5.00 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 $8.65 \mathrm{~g} / \mathrm{cm}^{3} .$ )

David Collins

Numerade Educator

Problem 91

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 92

When $\mathrm{H}_{2} \mathrm{O}_{2}$ is mixed with $\mathrm{Fe}^{2+}$, which redox reaction will occur-the oxidation of $\mathrm{Fe}^{2+}$ to $\mathrm{Fe}^{3+}$ or the reduction of $\mathrm{Fe}^{2+}$ to Fe? What are the $E_{\text {cenl }}^{\circ}$ values for the electrochemical cells corresponding to the two reactions?

Nicole Mabante

Numerade Educator

Problem 93

Calculate the potential of a cell consisting of two hydrogen electrodes, one immersed in a solution with (conc. $\left.\mathrm{H}^{+}\right)=1.0 \times 10^{-8} \mathrm{M}$ and the other with (conc. $\left.\mathrm{H}^{+}\right)=$
$0.025 \mathrm{M}$

Aadit Sharma

Numerade Educator

Problem 94

The permanganate ion $\mathrm{MnO}_{4}^{-}$ can be reduced to the manganese(II) ion $\mathrm{Mn}^{2+}$ in aqueous acidic solution, and the reduction potential for this half-cell reaction is $1.52 \mathrm{~V}$. If this half-cell is combined with a $\mathrm{Zn}^{2+} \mid Z n$ half-cell to form a galvanic 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 voltage.

Nicole Mabante

Numerade Educator

Problem 95

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 $12 \mathrm{~V} . \mathrm{A}$ large-scale plant can produce about $9.0$ metric tons of $\mathrm{F}_{2}$ gas per day.
(a) What mass in grams of $\mathrm{HF}$ is consumed?
(b) Using the conversion factor of $3.60 \times 10^{6} \mathrm{~J} / \mathrm{kWh}$, how much energy in kilowatt-hours is consumed by a cell operating at $6.0 \times 10^{3} \mathrm{~A}$ at $12 \mathrm{~V}$ for $24 \mathrm{~h}$ ?

David Collins

Numerade Educator

Problem 96

What reaction would take place if a $1.0-\mathrm{M}$ solution of $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ was added to a $1.0-\mathrm{M}$ solution of $\mathrm{HBr}$ ?

Aadit Sharma

Numerade Educator

Problem 97

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 98

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
$E_{\mathrm{cell}}=0.34 \mathrm{~V}$. What is the $\mathrm{pH}$ of the solution?
$$
\begin{array}{r}
2 \mathrm{H}_{2} \mathrm{O}(\ell)+2 \mathrm{H}_{2}(\mathrm{~g})+2 \mathrm{AgCl}(\mathrm{s}) \longrightarrow \\
2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})
\end{array}
$$

Aadit Sharma

Numerade Educator

Problem 99

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

David Collins

Numerade Educator

Problem 100

$E_{\text {cell }}=0.010 \mathrm{~V}$ for a galvanic 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) What is the equilibrium constant $K_{c}$ for the reaction?
(b) If a solution with (conc. $\mathrm{Pb}^{2+}$ ) $=1.1 \mathrm{M}$ had excess tin metal added to it, what would the equilibrium concentration of $\mathrm{Sn}^{2+}$ and $\mathrm{Pb}^{2+}$ be?

David Collins

Numerade Educator

Problem 101

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 $150.0 \mathrm{~mA}$, what electrolysis time should you use? The density of metallic silver is $10.5 \mathrm{~g} / \mathrm{cm}^{3}$.

David Collins

Numerade Educator

Problem 102

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

Aadit Sharma

Numerade Educator

Problem 103

A student wanted to measure the copper(II) concentration in an 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. If the cell gave $E_{\text {cell }}=$ $0.62 \mathrm{~V}$ at $25^{\circ} \mathrm{C}$, what was the copper(II) concentration of the solution?

David Collins

Numerade Educator

Problem 104

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 $1.35 \mathrm{~V} .$ How many hours can such a battery provide power at a rate of $4.0 \times 10^{-4}$ watt $\left(1\right.$ watt $=1 \mathrm{~J} \mathrm{~s}^{-1}$ ) if $1.25 \mathrm{~g} \mathrm{HgO}$ is available?

David Collins

Numerade Educator