6. Chemical Quantities & Aqueous Reactions

Redox Reactions

Practice Problem: Balancing Redox Reactions

What products are obtained in the electrolysis of a molten mix-
ture of KI and KBr?

Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. 
(c) LiOH

What is the pH of the solution in the cathode compartment of the following cell if the measured cell potential at 25 °C is 0.17 V?

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
a. Zn

Calculate ∆Gr°xn and K for each reaction. b. The reaction of Cr3+(aq) and Cr(s) to form Cr2+(aq). [The
electrode potential of Cr2+(aq) to Cr(s) is -0.91 V.]

(a) Sketch a cell with inert electrodes suitable for the elec-trolysis of an aqueous solution of sulfuric acid. Label the anode and cathode, and indicate the direction of electron and ion flow. Identify the positive and negative electrodes.
(b) Write balanced equations for the anode, cathode, and overall cell reactions.

Redox Reactions Example 1

The following cell reactions occur spontaneously:  
(a) Arrange the following reduction half-reactions in order of decreasing tendency to occur:

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions:
(c) Fe1s2 + 2 Fe3+1aq2 ¡ 3 Fe2+1aq2

A metal forms the fluoride MF3. Electrolysis of the molten fluo-
ride by a current of 3.86 A for 16.2 minutes deposits 1.25 g of the
metal. Calculate the molar mass of the metal.

During the discharge of an alkaline battery, 4.50 g of Zn 
is consumed at the anode of the battery. (b)
How many coulombs of electrical charge are transferred
from Zn to MnO2?

True or false: 
(a) If a substance is oxidized, there must be more oxygen in 
the substance.

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(a) Oxygen gas is bubbled through an acidic solution of Cr(NO3)3.

Which element is oxidized and which is reduced in each of the following reactions?
(b)

Hg in Hg(aq):oxidized; Cl in HgCl2(aq):reduced

Hg in Hg(aq):reduced; Cl in HgCl2(aq):oxidized

Hg in Hg(aq):oxidized; Hg in HgCl2(aq):reduced

Hg in Hg(aq):reduced; Hg in HgCl2(aq):oxidized

Which element is oxidized and which is reduced in the following reaction?Hg (aq) + HgCl2 (aq) → Hg2Cl2

The half-reactions that occur in ordinary alkaline batteries can be written as
 In 1999, researchers in Israel reported a new type of alkaline battery, called a “super-iron” battery. This battery uses the same anode reaction as an ordinary alkaline battery but involves the reduction of FeO42- ion (from K2FeO4) to solid Fe(OH)3 at the cathode. 
(a) Use the following standard reduction potential and any data from Appendixes C and D to calculate the stan-dard cell potential expected for an ordinary alkaline battery:
<QUESTION REFERENCES APPENDIX C AND D>

Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. 
(a) Ag2SO4

In the Brønsted–Lowry concept of acids and bases, acid–
base reactions are viewed as proton-transfer reactions.
The stronger the acid, the weaker is its conjugate base.
If we were to think of redox reactions in a similar way, what particle would be analogous to the proton? Would
strong oxidizing agents be analogous to strong acids or
strong bases? [Sections 20.1 and 20.2]

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions:
(d) 2 NO3-1aq2 + 8 H+1aq2 + 3 Cu1s2 ¡ 2 NO1g2 + 
4 H2O1l2 + 3 Cu2+1aq2

A voltaic cell employs the following redox reaction: Sn2+(aq) + Mn(s) ¡ Sn(s) + Mn2+(aq)
Calculate the cell potential at 25 °C under each set of conditions. c. [Sn2+] = 2.00 M; [Mn2+] = 0.0100 M

Experimental solid-oxide fuel cells that use butane (C4H10) as the fuel have been reported recently. These cells contain composite metal/metal oxide electrodes and a solid metal oxide electrolyte. The cell half-reactions are  
(b) Use the thermodynamic data in Appendix B to calculate the values of E° and the equilibrium constant K for the cell reaction at 25 °C. Will E° and K increase, decrease, or remain the same on raising the temperature?

Which of the following are redox reactions? For those that
are, indicate which element is oxidized and which is reduced.
For those that are not, indicate whether they are precipitation
or neutralization reactions.
(a) P41s2 + 10 HClO1aq2 + 6 H2O1l2¡ 4 H3PO41aq2 + 10 HCl1aq2

Copper reduces dilute nitric acid to nitric oxide (NO) but reduces concentrated nitric acid to nitrogen dioxide (NO2): Assuming that [Cu2+] = 0.10 M and that the partial pressures of NO and NO2 are 1.0 * 10-3 atm, calculate the potential (E) for reactions (1) and (2) at 25 °C and show which reaction has the greater thermodynamic tendency to occur when the concentration of HNO3 is
(a) 1.0 M

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(d) A nickel wire is dipped into an aqueous solution of HClO.

Consider a galvanic cell that uses the reaction  Calculate the potential at 25 °C for a cell that has the following ion concentrations: [Ag+] = 0.010M, [Ni2+] = 0.100M.

For the following half-reaction, E° = 1.103 V:  Calculate the formation constant Kf for Cu(CN)2-.

The following cell reactions occur spontaneously:  
(b) Which of these substances (A,A+,B,B+,C,C+) is the strongest oxidizing agent? Which is the strongest reducing agent?

Introduction to Oxidation Reduction (Redox) Reactions

Predict whether the following reactions will be spontaneous in acidic solution under standard conditions:
(c) reduction of Ce4+ to Ce3+ 
by H2O2,

A mercury battery uses the following electrode half-reactions:  
(c) What is the effect on the cell voltage of a tenfold change in the concentration of KOH in the electrolyte? Explain..

Consider the following half-reactions and E° values: 
(c) Write the cell reaction for part (b), and calculate the values of E°, ∆G° (in kilojoules), and K for this reaction at 25 °C

Which element is oxidized and which is reduced in each of the following reactions?
(a)

Sketch a cell with inert electrodes suitable for electrolysis of aqueous CuBr2. 
(b) Indicate the direction of electron and ion flow.

A sample of impure tin of mass 0.535 g is dissolved in strong
acid to give a solution of Sn2+. The solution is then titrated with a 0.0448 M solution of NO3-, which is reduced to NO(g). The equivalence point is reached upon the addition of 0.0344 L of the NO3- solution. Find the percent by mass of tin in the original sample, assuming that it contains no other reducing agents.

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(b) A strip of lead is dipped into an aqueous solution of AgNO3.

A battery relies on the oxidation of magnesium and the reduction of Cu2+. The initial concentrations of Mg2+ and Cu2+ are 1.0 * 10-4 M and 1.5 M, respectively, in 1.0-liter half-cells.
a. What is the initial voltage of the battery?

Indicate whether each of the following statements is true
or false:
(a) If something is oxidized, it is formally losing electrons.

Aqueous solutions of ammonia 1NH32 and bleach (active
ingredient NaOCl) are sold as cleaning fluids, but bottles
of both of them warn: “Never mix ammonia and bleach, as
toxic gases may be produced.” One of the toxic gases that
can be produced is chloroamine, NH2Cl. 
(e) Is N oxidized, reduced, 
or neither, upon the conversion of ammonia to nitrogen 
trichloride?

Silver can be electroplated at the cathode of an electrolysis cell by the half-reaction:
Ag+(aq) + e- ¡ Ag(s)
What mass of silver would plate onto the cathode if a current of
6.8 A flowed through the cell for 72 min?

You are on your dream vacation at the beach when a major storm knocks out the power for days. Your cell phone is dead, and you want to make a battery to charge it. You find the following materials in the beach house. blue stone algaecide for pools, which can be used to make a 1.0 M Cu2+ solution
alum in the kitchen, which can be used to make a 1.0 M Al3+ solution aluminum foil, copper wire, and bologna, which can be used as a salt bridge.
(d) An iPhone requires 5.0 V for charging. Can this battery charge the phone? Explain.

Tell for each of the following substances whether the oxidation number increases or decreases in a redox reaction.
(a) An oxidizing agent 
(b) A reducing agent 
(c) A substance undergoing oxidation 
(d) A substance undergoing reduction

Determine whether each reaction is a redox reaction. For each
redox reaction, identify the oxidizing agent and the reducing
agent.
a. 4 Li(s) + O2( g)¡2 Li2O(s)
b. Mg(s) + Fe2 + (aq)¡Mg2 + (aq) + Fe(s)

(d) Why are active metals such 
as Al obtained by electrolysis using molten salts rather than 
aqueous solutions?

What is the line notation for the galvanic cell? <img src="https://lightcat-files.s3.amazonaws.com/problem_images/a8a7a1536c6c7e29-1673979053099.jpg" alt="" />
(a) <EQUATION> 
(b) <EQUATION> 
(c) <EQUATION> 
(d) <EQUATION>

A voltaic cell utilizes the following reaction:
4 Fe2+1aq2 + O21g2 + 4 H+1aq2 ¡ 4 Fe3+1aq2 + 2 H2O1l2
(b) What is the emf of this cell when 3Fe2+4 = 1.3 M, 3Fe3+4=
0.010 M, PO2 = 0.50 atm, and the pH of the solution in the
cathode half-cell is 3.50?

The diagram that follows represents a molecular view of a
process occurring at an electrode in a voltaic cell.
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/bca278059c130b10-1667395861943.jpg" alt="" />
(c) Why are the 
atoms in the electrode represented by larger spheres than 
those in the solution? [Section 20.3]

Determine whether or not each redox reaction occurs spontaneously in the forward direction.
b. 2 Ag+(aq) + Ni(s) ¡ 2 Ag(s) + Ni2+(aq)

The standard reduction potentials of the following halfreactions are given in Appendix E:
Ag+1aq2 + e- ¡ Ag1s2
Cu2+1aq2 + 2 e- ¡ Cu1s2
Ni2+1aq2 + 2 e- ¡ Ni1s2
Cr3+1aq2 + 3 e- ¡ Cr1s2
(b) Determine which
combination of these half-cell reactions leads to the cell
reaction with the smallest positive cell potential and calculate the value.

Heart pacemakers are often powered by lithium–silver
chromate “button” batteries. The overall cell reaction is
2 Li1s2 + Ag2CrO41s2 ¡ Li2CrO41s2 + 2 Ag1s2
(b) Choose
the two half-reactions from Appendix E that most closely
approximate the reactions that occur in the battery. What
standard emf would be generated by a voltaic cell based on
these half-reactions?

A voltaic cell is constructed that is based on the following
reaction:
Sn2+1aq2 + Pb1s2 ¡ Sn1s2 + Pb2+1aq2
(a) If the concentration of Sn2+ in the cathode half-cell is
1.00 M and the cell generates an emf of +0.22 V, what is
the concentration of Pb2+ in the anode half-cell?

A student designs an ammeter (a device that measures
electrical current) that is based on the electrolysis of water
into hydrogen and oxygen gases. When electrical current
of unknown magnitude is run through the device for 2.00
min, 12.3 mL of water-saturated H21g2 is collected. The
temperature of the system is 25.5 °C, and the atmospheric
pressure is 768 torr. What is the magnitude of the current in
amperes?

If a reaction has an equilibrium constant K 6 1, is E° posi-tive or negative? What is the value of K when E° = 0 V?

An H2/H+ half-cell (anode) and an Ag+/Ag half cell (cathode) are connected by a wire and a salt bridge. 
(a) Sketch the cell, indicating the direction of electron and ion flow.

Write equations for the half-reactions that occur in the electrol- ysis of molten potassium bromide.

A Cu/Cu2+ concentration cell has a voltage of 0.22 V at 25 °C. The concentration of Cu2+ in one of the half-cells is 1.5x10^-3 M. What is the concentration of Cu2+ in the other half-cell? (Assume the concentration in the unknown cell is the lower of the two concentrations.)

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written.
a. O2(g) + 2 H2O(l) + 4 Ag(s) ¡ 4 OH-(aq) + 4 Ag+(aq)

Determine whether each reaction is a redox reaction. For each
redox reaction, identify the oxidizing agent and the reducing
agent.
c. Pb(NO3)2(aq) + Na2SO4(aq)¡PbSO4(s) + 2 NaNO3(aq)
d. HBr(aq) + KOH(aq)¡H2O(l ) + KBr(aq)

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(c) A silver wire is immersed in an aqueous solution of NiCl2.

(b) Write the half-reaction that occurs 
at a hydrogen electrode in acidic aqueous solution when 
it serves as the anode of a voltaic cell.

For each of the following reactions, write a balanced
equation, calculate the standard emf, calculate ∆G° at
298 K, and calculate the equilibrium constant K at 298 K.
(b) In acidic solution, copper(I) ion is oxidized to copper(II) 
ion by nitrate ion. 

Consider the reaction shown here occurring at 25 °C. Cr(s) + Cd2+(aq) ¡ Cr2+(aq) + Cd(s)
Determine Ec°ell, K, and ∆Gr°xn for the reaction and complete the table. [Cd2+]
[Cr2+]
Q
Ecell
𝚫Grxn 1.00
1.00
1.00 * 10-5
4.18 * 10-4
1.00
1.00 * 10-5
1.00
1.00<img src="https://lightcat-files.s3.amazonaws.com/problem_images/fe8034d17334b73f-1674680818578.jpg" alt="" />

Oxidation-Reduction in Aqueous Solutions

The nickel–iron battery has an iron anode, an NiO(OH) cathode, and a KOH electrolyte. This battery uses the follow-ing half-reactions and has an E° value of 1.37 V at 25 °C.  
(b) Calculate ∆G° (in kilojoules) and the equilibrium con-stant K for the cell reaction at 25 °C.

The cell potential of this electrochemical cell depends on the gold concentration in the cathode half-cell.
Pt(s) | H2(g, 1.0 atm) | H+(aq, 1.0 M) || Au3+(aq, ? M) | Au(s)
What is the concentration of Au3+ in the solution if Ecell is 1.22 V?

For each of the following reactions, write a balanced
equation, calculate the standard emf, calculate ∆G° at
298 K, and calculate the equilibrium constant K at 298 K.
(a) Aqueous iodide ion is oxidized to I21s2 by Hg22+1aq2.

A storm has knocked out power to your beach house, and you would like to build a battery from household items to charge your iPhone. You have the following materials. alum in the kitchen, which can be used to make a 1.0 M Al3+ solution bleach, which is a solution that is approximately a 1.0 M in ClO-aluminum foil, a platinum necklace and bologna, which can be used as a salt bridge 
(b) What voltage can be generated?

An electrochemical cell is based on these two half-reactions:
Ox: Pb(s) -> Pb2+ (aq, 0.10 M) + 2 e- Red: MnO4-(aq, 1.50 M) + 4 H+(aq, 2.0 M) + 3 e- -> MnO2(s) + 2 H2O(l)
Calculate the cell potential at 25 °C.

A voltaic cell utilizes the following reaction:
Al1s2 + 3 Ag+1aq2 ¡ Al3+1aq2 + 3 Ag1s2
What is the effect on the cell emf of each of the following
changes? (a) Water is added to the anode half-cell, diluting the solution.

Calculate E° for each of the following reactions, and tell which are spontaneous under standard-state conditions.
(a) <CHEMICAL EQUATION>

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
b. Cr

A voltaic cell utilizes the following reaction:
(b) What is the emf for this cell when 3Fe3+4 = 3.50 M, PH2=
0.95 atm, 3Fe2+4 = 0.0010 M, and the pH in both half-cells
is 4.00?

An electrochemical cell is based on these two half-reactions:
Ox: Sn(s) ¡ Sn2+(aq, 2.00 M) + 2 e-
Red: ClO2(g, 0.100 atm) + e- ¡ ClO2-(aq, 2.00 M) Calculate the cell potential at 25 °C.

Write the shorthand notation for a galvanic cell that uses the following cell reaction. Include inert electrodes if necessary.
2 Fe1s2 + Cr2O72-1aq2 + 14 H+1aq2¡2 Fe3+1aq2 + 2 Cr3+1aq2 + 7 H2O1l2

Which element is oxidized, and which is reduced in the 
following reactions? 
(a) N21g2 + 3 H21g2¡2 NH31g2

(a) Which reaction is spontaneous in the hydrogen fuel
cell: hydrogen gas plus oxygen gas makes water, or water
makes hydrogen gas plus oxygen gas?

A voltaic cell consists of a Pb>Pb half-cell and a Cu>Cu half- cell at 25°C. The initial concentrations of Pb2+ and Cu2+ are 0.0500 M and 1.50 M, respectively. b. What is the cell potential when the concentration of Cu2+ has fallen to 0.200 M?

Indicate whether each of the following statements is true
or false:
(c) An oxidizing agent is needed to convert CO into CO2.

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(c) Chlorine gas is bubbled through aqueous H2C2O4.

A voltaic cell is constructed that uses the following half-cell
reactions:
Cu+1aq2 + e- ¡ Cu1s2
I21s2 + 2 e- ¡ 2 I-1aq2
The cell is operated at 298 K with 3Cu+4 = 0.25 M and
3I-4 = 0.035 M. (a) Determine E for the cell at these concentrations.

Hydrazine 1N2H42 and dinitrogen tetroxide 1N2O42 form 
a self-igniting mixture that has been used as a rocket propellant. The reaction products are N2 and H2O.
(c) Which substance serves as the reducing agent and which as the oxidizing agent?

In order to charge a lead storage battery (Section 19.10) 500.0 g of PbSO4(s) must be converted into PbO2(s) and Pb(s).
(a) Does the reaction represent an electrolytic or galvanic cell?

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(d) Hydrogen gas is bubbled through aqueous Cd(NO3)2.

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written.
c. PbO2(s) + 4 H+(aq) + Sn(s) ¡ Pb2+(aq) + 2H2O(l) + Sn2+(aq)

(a) Which region of the periodic table shown here contains 
elements that are easiest to oxidize? (b) Which region contains 
the least readily oxidized elements?<img src="https://lightcat-files.s3.amazonaws.com/problem_images/d1040041796583b4-1660739570184.jpg" alt="" />

Indicate whether each of the following statements is true
or false:
(c) If there are no changes in the oxidation state of the reactants or products of a particular reaction, that reaction is not a redox reaction.

The commercial production of nitric acid involves the
following chemical reactions:
4 NH31g2 + 5 O21g2¡4 NO1g2 + 6 H2O1g2
2 NO1g2 + O21g2¡2 NO21g2
3 NO21g2 + H2O1l2¡2 HNO31aq2 + NO1g2
(a) Which of these reactions are redox reactions?

Potassium superoxide, KO2, is often used in oxygen masks
(such as those used by firefighters) because KO2 reacts with
CO2 to release molecular oxygen. Experiments indicate that 2
mol of KO21s2 react with each mole of CO21g2. (b) Indicate
the oxidation number for each atom involved in the reaction
in part (a). What elements are being oxidized and reduced?

A voltaic cell consists of a Zn>Zn2+ half-cell and a Ni>Ni2+ half-cell at 25 °C. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively. c. What are the concentrations of Ni2+ and Zn2+ when the cell potential falls to 0.45 V?
Ec°ell for the fuel-cell breathalyzer, which employs the following

Gold exists in two common positive oxidation states, +1
and +3. The standard reduction potentials for these oxidation states are
Au+1aq2 + e- ¡ Au1s2 Ered ° = +1.69 V
Au3+1aq2 + 3 e- ¡ Au1s2 Ered ° = +1.50 V
(c) Miners obtain gold by soaking gold-containing ores 
in an aqueous solution of sodium cyanide. A very soluble 
complex ion of gold forms in the aqueous solution because 
of the redox reaction 
4 Au1s2 + 8 NaCN1aq2 + 2 H2O1l2 + O21g2 
¡ 4 Na3Au1CN2241aq2 + 4 NaOH1aq2 
What is being oxidized, and what is being reduced in this 
reaction?

What is meant by cathodic protection? 
(a) Steel is coated with a layer of paint.
(b) Iron in steel is oxidized to form a protective oxide coating.
(c) Steel is coated with zinc because zinc is more easily oxidized than iron.
(d) A strip of magnesium is attached to steel because the magnesium is more easily oxidized than iron.

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(b) An acidic solution of FeSO4 is exposed to oxygen.

Beginning with the equations that relate E°, ∆G°, and K, show that ∆G° is negative and K 7 1 for a reaction that has a positive value of E°

Given the following half-reactions and E° values,  write a balanced equation for the formation of Mn2+ and MnO2 from Mn3+, and calculate the value of E° for this reaction. Is the reaction spontaneous under standard-state conditions?

Which of the following describes the process of galvanization that protects steel from rusting?
(a) Steel is coated with a layer of paint. 
(b) Iron in steel is oxidized to form a protective oxide coating.
(c) Steel is coated with zinc because zinc is more easily oxidized than iron.
(d) A strip of magnesium is attached to steel because the magnesium is more easily oxidized than iron.

Consider the redox titration of 100.0 mL of a solution of 0.010 M Fe2+ in 1.50 M H2SO4 with a 0.010 M solution of KMnO4, yielding Fe3+ and Mn2+. The titration is carried out in an electrochemical cell equipped with a platinum electrode and a calomel reference electrode consisting of an Hg2Cl2/Hg electrode in contract with a saturated KCl solution having [Cl-] = 2.9M. Using any data in Appendixes C and D, calculate the cell potential after addition of (a) 5.0 mL, (b) 10.0mL, (c) 19.0 mL, and (d) 21.0 mL of the KMnO4 solution.

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. <QUESTION REFERENCES APPENDIX D>
(d) Reduction of I2(s) by H2SO3(aq)

What products should be formed when the following reac-tants are electrolyzed in a cell having inert electrodes? Account for any differences. 
(b) Aqueous KCl

Oxidizing Agent is reduced and in turn oxidizes another element/compound.Reducing Agent is oxidized and in turn reduces another element/compound.

Treatment of gold metal with BrF3 and KF produces Br2 and
KAuF4, a salt of gold. Identify the oxidizing agent and the reducing
agent in this reaction.

Disulfides are compounds that have S ¬ S bonds, like peroxides have O ¬ O bonds. Thiols are organic compounds
that have the general formula R ¬ SH, where R is a generic
hydrocarbon. The SH- ion is the sulfur counterpart of
hydroxide, OH-. Two thiols can react to make a disulfide,
R ¬ S ¬ S ¬ R.
(c) If you react two thiols to make a disulfide, are you 
oxidizing or reducing the thiols?

True or false: 
(a) Reduction occurs if the oxidation number of an element 
increases

Calculate ∆Gr°xn and K for each reaction. a. The reaction of Cr2+(aq) with Cr2O7^2-(aq) in acid solution to form Cr3+(aq).

Write balanced equations for the electrode and overall cell reactions in the following galvanic cells. Sketch each cell, labeling the anode and cathode and showing the direction of electron and ion flow.
(a) .

The Nernst equation applies to both cell reactions and half-reactions. For the conditions specified, calculate the potential for the following half-reactions at 25 °C.

(b) <CHEMICAL EQUATION>

The following cell reactions occur spontaneously:  
(c) Which of the three cell reactions delivers the highest voltage?

Consider a galvanic cell that uses the following half-reactions: 
(b) What is the oxidizing agent, and what is the reducing agent?.

Calculate the equilibrium constant for the reaction between Fe2+(aq) and Zn(s) (at 25 °C).

 Correct, the lead in lead(II) oxide is reduced. 

 The nitrogen in ammonia is oxidized and therefore the reducing agent. 

 Nitrogen is a product of the reaction.  The oxidizing agent is a reactant. 

 Water is a product of the reaction.  The oxidizing agent is a reactant. 

 Lead is a product of the reaction.  The oxidizing agent is a reactant. 

 Both lead and nitrogen change oxidation states in this reaction. 

 In a redox reaction, the oxidizing agent oxidizes another substance (and is itself reduced). 

What is the oxidizing agent in the following reaction?3 PbO (s) + 2 NH3 (aq) &#8594; N2 (g) + 3 H2O (l) + 3 Pb (s)

Determine whether or not each redox reaction occurs spontaneously in the forward direction.
a. Ni(s) + Zn2+(aq) ¡ Ni2+(aq) + Zn(s)

Which element is oxidized, and which is reduced in the 
following reactions? 
(c) Cl21aq2 + 2 NaI1aq2¡I21aq2 + 2 NaCl1aq2

To remember the difference between oxidation and reduction just learn:LEO the lion goes GER

Calculate the number of kilowatt-hours of electricity
required to produce 1.0 * 103 kg (1 metric ton) of aluminum by electrolysis of Al3+ if the applied voltage is 4.50 V
and the process is 45% efficient.

(d) Why is 
sodium metal not obtained when an aqueous solution of 
NaCl undergoes electrolysis?

Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. 
(b) CuCl2

For each of the following reactions, write a balanced
equation, calculate the standard emf, calculate ∆G° at
298 K, and calculate the equilibrium constant K at 298 K.
(c) In basic solution, Cr1OH231s2 is oxidized to CrO42-1aq2 by ClO-1aq2.

A major source of sodium metal is the electrolysis of molten so-
dium chloride. What magnitude of current produces 1.0 kg of
sodium metal in 1 hour?

Where in the periodic table are the best reducing agents found? The best oxidizing agents?

Consider a galvanic cell that utilizes the following half-reactions:
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/089351c803a2cf4b-1674069483425.jpg" alt="" /> 
<QUESTION REFERS TO APPENDIX B> 
(b) What are the values of E° and the equilibrium constant K for the cell reaction at 25 °C?

Electrolysis of a metal nitrate solution M(NO3)2(aq) for 325 min with a constant current of 20.0 A gives 111 g of the metal. Identify the metal ion M2+.

What reaction can occur, if any, when the following experiments are carried out under standard-state conditions? 
(a) A strip of zinc is dipped into an aqueous solution of Pb(NO3)2.

Which of the following represents an oxidation-reduction reaction?&nbsp;I. PCl3 (aq) + Cl2 (g) → PCl5 (aq)&nbsp;II. 2 AgNO3 (aq) + Cu (s) → Cu(NO3)2 (aq) + 2 Ag (s)&nbsp;III. CO2 (g) + 2 LiOH (aq) → Li2CO3 (aq) + H2O (l)IV. FeCl2 (aq) + 2 NaOH (aq) → Fe(OH)2 (aq) + 2 NaCl (aq)&nbsp;

A voltaic cell consists of a Zn>Zn2+ half-cell and a Ni>Ni2+ half-cell at 25 °C. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively.
b. What is the cell potential when the concentration of Ni2+ has fallen to 0.500 M?

Magnesium metal is produced by the electrolysis of molten magnesium chloride using inert electrodes. 
(a) Sketch the cell, label the anode and cathode, indicate the sign of the electrodes, and show the direction of electron and ion flow.

What is the Fe2+: Sn2+ concentration ratio in the following cell at 25 °C if the measured cell potential is 0.35 V?

How does the pH of the solution affect the formation of rust?

Which of the following metals can offer cathodic protec-tion to iron? Select all the correct choices. Mn, Ni, Pb, Sn, Al

What is the pH of the solution in the cathode compartment of the following cell if the measured cell potential at 25 °C is 0.58 V? (Refer to Appendix B for standard reduction potentials.) <QUESTION REFERENCES TABLE 19.1>
(a) 8.0
(b) 4.5
(c) 2.2
(d) 3.0

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
c. Mn

(c) What process occurs at the anode in the electrolysis of molten NaCl?

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written.
b. MnO2(aq) + 4 H+(aq) + Zn(s) ¡
Mn2+(aq) + 2H2O(l) + Zn2+(aq)

(b) Given 
the following reduction potentials, calculate the standard 
emf of the cell: 
Cd1OH221s2 + 2 e- ¡ Cd1s2 + 2 OH-1aq2 
E°red = -0.76 V 
NiO1OH21s2 + H2O1l2 + e- ¡ Ni1OH221s2 + OH-1aq2 
E°red = +0.49 V

Oxidation and Reduction (Redox) Reactions Step-by-Step Example

What products are obtained in the electrolysis of molten NaI?

Draw an electrolytic cell in which Mn2+ is reduced to Mn and Sn
is oxidized to Sn2+. Label the anode and cathode, indicate the direction of electron flow, and write an equation for the half- reaction occurring at each electrode. What minimum voltage is necessary to drive the reaction?

Identify the oxidizing agent and reducing agent from the following redox reaction.&nbsp;Ba (s) + Cl2 (g) → BaCl2 (aq)

When suspected drunk drivers are tested with a Breathalyzer, the alcohol (ethanol) in the exhaled breath is oxidized to acetic acid with an acidic solution of potassium dichromate: <CHEMICAL EQUATION> The color of the solution changes because some of the orange Cr2O7
2-is converted to the green Cr3+ The Breath-alyzer measures the color change and produces a meter reading calibrated in blood alcohol content. 

(a) What is E° for the reaction if the standard half-cell potential for the reduction of acetic acid to ethanol is 0.058 V?

A voltaic cell utilizes the following reaction:
2 Fe3+1aq2 + H21g2 ¡ 2 Fe2+1aq2 + 2 H+1aq2
(a) What is the emf of this cell under standard conditions?

Calculate the equilibrium constant for each of the reactions in Problem 65.

The commercial production of nitric acid involves the
following chemical reactions:
4 NH31g2 + 5 O21g2¡4 NO1g2 + 6 H2O1g2
2 NO1g2 + O21g2¡2 NO21g2
3 NO21g2 + H2O1l2¡2 HNO31aq2 + NO1g2
(b) Identify the element undergoing oxidation and the element undergoing reduction.
3 NO21g2 + H2O1l2¡2 HNO31aq2 + NO1g2

Identify the element that gets oxidized and the oxidizing agent in the reaction. (LO 4.19) 
(a) 
(b) 
(c) 
(d)

A Level Chemistry Revision "Introduction to Redox Reactions"

A voltaic cell consists of a Pb>Pb half-cell and a Cu>Cu half- cell at 25°C. The initial concentrations of Pb2+ and Cu2+ are 0.0500 M and 1.50 M, respectively. a. What is the initial cell potential?

You are on your dream vacation at the beach when a major storm knocks out the power for days. Your cell phone is dead, and you want to make a battery to charge it. You find the following materials in the beach house. blue stone algaecide for pools, which can be used to make a 1.0 M Cu2+ solution
alum in the kitchen, which can be used to make a 1.0 M Al3+ solution aluminum foil, copper wire, and bologna, which can be used as a salt bridge.
(b) What voltage can be generated?

Determine whether each reaction is a redox reaction. For each
redox reaction, identify the oxidizing agent and the reducing
agent.
a. Al(s) + 3 Ag+ (aq)¡Al3 + (aq) + 3 Ag(s)
b. SO3( g) + H2O(l )¡H2SO4(aq)
c. Ba(s) + Cl2( g)¡BaCl2(s)
d. Mg(s) + Br2(l )¡MgBr2(s)

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. <QUESTION REFERENCES APPENDIX D>
(b) Reduction of Ni2+(aq) by Sn2+(aq)

Oxidation-Reduction Reactions

What are the products of the overall reaction in the elec-trolysis of an aqueous solution of sodium hydroxide? (Refer to Table 19.1 for standard reduction potentials.)
(a) Na(s) and O2(g)
(b) H2(g) and O2(g)
(c) Na(s) and H2(g) 
(d) Na(s) and H2O2(aq)

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
b. Sn

Porous pellets of TiO2 can be reduced to titanium metal at the cathode of an electrochemical cell containing molten CaCl2 as the electrolyte. When the TiO2 is reduced, the O2-ions dis-solve in the CaCl2 and are subsequently oxidized to O2 gas at the anode. This approach may be the basis for a less expensive process than the one currently used for producing titanium.
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/990e6d90be840896-1673905726100.jpg" alt="" /> 
(c) Write balanced equations for the anode, cathode, and overall cell reactions.

A voltaic cell consists of a Pb>Pb half-cell and a Cu>Cu half- cell at 25°C. The initial concentrations of Pb2+ and Cu2+ are 0.0500 M and 1.50 M, respectively. c. What are the concentrations of Pb2+ and Cu2+ when the cell potential falls to 0.35 V?

Calculate Ec°ell for each balanced redox reaction and determine if the reaction is spontaneous as written.
a. 2 Cu(s) + Mn2+(aq) ¡ 2 Cu+(aq) + Mn(s)

A mercury battery uses the following electrode half-reactions:  
(b) Calculate ∆G° (in kilojoules) and K at 25 °C for the cell reaction.

Using the standard reduction potentials listed in Appendix
E, calculate the equilibrium constant for each of the following reactions at 298 K:
(c) 10 Br -1aq2 + 2 MnO4-1aq2 + 16 H+1aq2 ¡
2 Mn2+1aq2 + 8 H2O1l2 + 5 Br21l2

Write equations for the half-reactions that occur at the anode
and cathode for the electrolysis of each aqueous solution. a. Ni(NO3)2(aq)

Consider a Daniell cell with 1.0 M ion concentrations: <img src="https://lightcat-files.s3.amazonaws.com/problem_images/24c95afcb82444b1-1673966817776.jpg" alt="" /> Does the cell voltage increase, decrease, or remain the same when each of the following changes is made? Explain. 
(a) Write a balanced equation for each cell reaction.

Redox reactions

GCSE Chemistry - Oxidation and Reduction - Redox Reactions #39 (Higher Tier)

Use line notation to represent each electrochemical cell in
Problem 43.

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
a. Mg

Refer to the tabulated values of ∆Gf° in Appendix IIB to calculate Ec°ell for the fuel-cell breathalyzer, which employs the following reaction. ((∆G° for HC H O (g) = -374.2 kJ>mol.) CH3CH2OH(g) + O2(g) ¡ HC2H3O2(g) + H2O(g)

A current of 11.3 A is applied to 1.25 L of a solution of 0.552 M HBr converting some of the H+ to H2(g), which bubles out of solution. What is the pH of the solution after 73 minutes?

To what pH should you adjust a standard hydrogen electrode to
get an electrode potential of -0.122 V? (Assume that the partial pressure of hydrogen gas remains at 1 atm.)

Magnesium, the element, is produced commercially by
electrolysis from a molten salt (the “electrolyte”) using a
cell similar to the one shown here. (c) Recall that in an 
electrolytic cell the anode is given the + sign and the cathode is given the – sign, which is the opposite of what we see 
in batteries. What half-reaction occurs at the anode in this 
electrolytic cell? 

<img src="https://lightcat-files.s3.amazonaws.com/problem_images/a8cbcef5e91e582a-1667395281969.jpg" alt="" />

The following galvanic cell has a potential of 1.214 V at 25 °C:  Calculate the value of Ksp for Hg2Br2 at 25°C

What constant current (in amperes) is required to produce aluminum by the Hall–Héroult process at a rate of 40.0 kg/h?

Consider the following substances: Fe(s), PbO2(s), H+(aq), Al(s), Ag(s), Cr2O72-(aq).
(a) Look at the E° values in Appendix D, and classify each substance as an oxidizing agent or a reducing agent. <PROBLEM REFERENCES APPENDIX D>

A voltaic cell consists of a Zn>Zn2+ half-cell and a Ni>Ni2+ half-cell at 25 °C. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively.
a. What is the initial cell potential?

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
c. Cu

At one time on Earth, iron was present mostly as iron(II). Later, once plants had produced a significant quantity of oxygen in the atmosphere, the iron became oxidized to iron(III). Show that Fe2+(aq) can be spontaneously oxidized to Fe3+(aq) by O2(g) at 25°C assuming the following reasonable environmental conditions: <CHEMICAL EQUATION>

In each of the following instances, tell whether the substance gains electrons or loses electrons in a redox reaction. 
(a) An oxidizing agent 
(b) A reducing agent 
(c) A substance undergoing oxidation 
(d) A substance undergoing reduction

An MnO2(s)/Mn2+(aq) electrode in which the pH si 10.24 is prepared. Find the [Mn2+] necessary to lower the potential of the half-cell to 0.00 V (at 25°C)

Which element is being reduced in the following reaction?&nbsp;Cr2O72- + 3 HNO2 + 5 H+&nbsp;→ 2 Cr3+ + &nbsp;3NO3- + 4 H2O

(b) On which
side of an oxidation half-reaction do the electrons appear?

The cell potential of this electrochemical cell depends on the
pH of the solution in the anode half-cell.
Pt(s) | H2(g, 1 atm) | H+(aq, ? M) || Cu2+(aq, 1.0 M) | Cu(s) What is the pH of the solution if Ecell is 355 mV?

A galvanic cell has an iron electrode in contact with 0.10 M FeSO4 and a copper electrode in contact with a CuSO4 solu-tion. If the measured cell potential at 25 °C is 0.67 V, what is the concentration of Cu2+ in the CuSO4 solution?

When suspected drunk drivers are tested with a Breathalyzer, the alcohol (ethanol) in the exhaled breath is oxidized to acetic acid with an acidic solution of potassium dichromate: <CHEMICAL EQUATION> The color of the solution changes because some of the orange Cr2O7
2-is converted to the green Cr3+ The Breath-alyzer measures the color change and produces a meter reading calibrated in blood alcohol content. 

(b) What is the value of E for the reaction when the concentrations of ethanol, acetic acid, Cr2O7 are 1.0 M and the pH is 4.00?

Experimental solid-oxide fuel cells that use butane (C4H10) as the fuel have been reported recently. These cells contain composite metal/metal oxide electrodes and a solid metal oxide electrolyte. The cell half-reactions are 
<QUESTION REFERS TO APPENDIX B> 
(c) How many grams of butane are required to produce a constant current of 10.5 A for 8.00 h? How many liters of gaseous butane at 20 °C and 815 mm Hg pressure are required?

Write a balanced equation for the overall cell reaction in the following galvanic cell, and tell why inert electrodes are required at the anode and cathode.
Pt(s) | Br-(aq) | Br2(l2) || Cl2(g) | Cl-(aq) || Pt(s)

The accompanying photo shows the reaction between a
solution of Cd1NO322 and one of Na2S. 
(d) Is this a redox reaction?

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions:
(a) Cl21g2 + 2 I-1aq2 ¡ 2 Cl-1aq2 + I21s2

What Are Redox Reactions? (Oxygen Exchange) | Reactions | Chemistry | FuseSchool

A voltaic cell that uses the reaction
PdCl42-1aq2 + Cd1s2 ¡ Pd1s2 + 4 Cl-1aq2 + Cd2+1aq2
has a measured standard cell potential of +1.03 V. 
(b) By using data from Appendix
E, determine E°red for the reaction involving Pd.

Use the data in Appendix D to predict whether the following reactions can occur under standard-state conditions. <QUESTION REFERENCES APPENDIX D>
(c) Oxidation of Ag(s) by Pb2+(aq)

A voltaic cell is constructed that uses the following reaction
and operates at 298 K:
Zn1s2 + Ni2+1aq2 ¡ Zn2+1aq2 + Ni1s2
(c) What is the emf of the cell when 
3Ni2+4 = 0.200 M and 3Zn2+4 = 0.900 M?

A voltaic cell utilizes the following reaction:
4 Fe2+1aq2 + O21g2 + 4 H+1aq2 ¡ 4 Fe3+1aq2 + 2 H2O1l2
(a) What is the emf of this cell under standard conditions?

The standard potential for the following galvanic cell is 0.40 V: (Europium, Eu, is one of the lanthanide elements.) Use the data in Table 19.1 to calculate the standard reduction potential for Eu3+/Eu2+ half-cell. <PROBLEM REFERENCES TABLE 19.1>

(a) A Cr3+1aq2 solution is electrolyzed, using a current of
7.60 A. What mass of Cr(s) is plated out after 2.00 days?