Back to Redox Resource Page

1) Which most readily gains electrons?

Cu

Cu^+2

Fe^+2

Zn^+2

Au^+3 most readily gains electrons

2) Which most readily loses electrons?

Hg(l)

Cu^+2

Sn^+4

Ba most readily loses electrons

Al

Calculate the cell potentials or voltages (E⁰). Indicate spontaneity.

3. Cl₂ + 2Br^- -----> 2Cl^- + Br₂ E⁰= + 0.27 v spontaneous

4. 2MnO₄^- + 5Pb + 16H⁺ -----> 2Mn⁺² + 8H₂O + 5Pb⁺² E⁰= + 1.64 v spontaneous

5. Will AgNO₃ react with Zn? Write a balanced redox reaction and calculate E^o

2Ag⁺ + Zn ------> 2Ag + Zn⁺² E⁰= + 1.56 v spontaneous Yes!

6. What would happen if you used an iron spoon to stir a soulution of Al₂(SO₄)₃(aq) ? Write a balanced redox reaction and calculate E^o.

3Fe + 2Al⁺³ ------> 3Fe⁺² + 2Al E⁰= - 1.21 v nonspontaneous No reaction!

7) What are the differences between an electrochemical cell and an electrolytic cell?

electrochemical cell	electrolytic cell
Produces electricity	Consumes electricity
Spontaneous	Nonspontaneous
Salt bridge Two beakers	No salt bridge One beaker
Metal Electrodes	Inert C or Pt Electrodes

8) What are the similarities between an electrochemical cell and an electrolytic cell?

electrochemical cell or electrolytic cell

The Anode is the site of oxidation and the cathode is the site of reduction.

Anions migrate to the anion and cations migrate to the cathode.

Both have redox reactions.

Electrons flow through a wire from the anode to the cathode

9) State how you would determine each of the following in an electrochemical or electrolytic cell.

	Electrochemical Cell	Electrolytic Cell
The site of reduction	Highest on Reduction Chart	The Negative Electrode
The site of oxidation	Lowest on Reduction Chart	The Positive Electrode
The +ve electrode	Site of Reduction	Connected to the power supply +ve
The -ve electrode	Site of Oxidation	Connected to the power supply -ve
The anions migrate to the	Anode	Anode
The cations migrate to the	Cathode	Cathode
The electrode that gains mass	Cathode	Neither inert electrodes
The electrode that loses mass	Anode	Neither inert electrodes
The electrons flow from	Anode to Cathode	Anode to Cathode

10.a) Draw an operating electrochemical cell using an Al half-cell and a Mg half-cell. Label the parts of the electrochemical cell including the anode or cathode, and all reagents and materials used. Write the reactions and determine the E⁰.

Cathode Reaction: 2(Al⁺³ + 3e^- ------> Al ) E⁰= - 1.66

Anode Reaction: 3(Mg -------> Mg⁺² + 2e^- ) E⁰= +2.37

Redox Reaction: 2Al⁺³ + 3Mg -----> 3 Mg⁺² + 2 Al E⁰= +0.71

11. (a) Write the half reaction that occurs at each electrode during the electrolysis of aqueous 1 M NaI.

Anode : 2I- --------> I2 + 2e^- E⁰= -0.54 v

Cathode : 2H2O + 2e- ------> H2 + 2OH- E0= -0.41v

(b) What is the minimum required voltage for this process? E⁰= +0.95 v

12. (a) Write the half reaction that occurs at each electrode during the electrolysis of molton NaI.

Anode : 2I^- --------> I2 + 2e^- E⁰= -0.54 v

Cathode : Na⁺ + 1e^- ------> Na E⁰= -2.71v

(b) What is the minimum required voltage for this process? E⁰= +3.25v

13. Aluminum is produced industrially from aluminum oxide, Al₂O₃. Demonstrate your understanding of this process by

(i) describing how the process is carried out: C electrodes are used in the electrolysis of molten Al₂O₃.

(ii) writing equations of the reactions involved in the process, and

Anode : 2O^-2 --------> O₂ + 4e^- Cathode : Al⁺³ + 3e^- ------> Al

(iii) describing how the problem of the high melting point of Al₂O₃ is overcome.

Mixing Al₂O₃ with cryolyte lowers the melting point from 2000º C to 900ºC, which is suitable for electrolysis.

14. Consider the following redox data:

3V + 2Ga³⁺ ----> 3V²⁺ + 2Ga E=+0.64V

3V²⁺ + 2Al ----> 3V + 2 Al³⁺ E=+0.46V

Based on these observations, a student concludes that Ga⁺³ and Al will react spontaneously. List the oxidizing agents in order of decreasing strength. Write reduction reactions for each. Determine the strongest reducing agent. Determine if Ga⁺³ and Al will react spontaneously.

strongest oxidizing agent	Ga^3+ + 3e^- ----> Ga
	V^2+ + 2e^-----> 3V
	Al^3+ + 3e^- ----> Al	strongest reducing agent

Ga⁺³ and Al will react spontaneously as Ga⁺³ is a stronger oxidizing agent than Al⁺³.

15. Balance the equation for the following half reaction occuring in acid solution:

7 H₂O + 2V ----> HV₂O₇^-3 + 13H⁺ + 10e^-

16. Balance the following redox reaction occuring in basic solution:

4 H₂O + 2 MnO₄^- + 3 C₂O₄^-2 -----> 2 MnO₂ + 8 OH^- + 6 CO₂

17. 250ml .200M MnO_4- reacts with excess SO₃^-2. How many grams of MnO₂ are produced?

2MnO₄^- + 3SO₃^-2 + H₂O -----> 2MnO₂ + 3SO₄^-2 + 2OH^- 4.35g MnO₂

18. Determine the oxidation number for each bold atom.

MnO2	IO3^-	Cr2O7^-2	C2O4^-2	Al(NO3)3	NH4Cl	NaH
+4	+5	+6	+3	+3	-3	-1
HOOH	NO3^-	H3PO4	Na2C2O4	I2	N2O3	Pt(H2O)4^+2
-1	+5	+5	+3	0	+3	+2

19. 250ml of .500M MnO₄^- are required to titrate a 100ml sample of SO₃^-2. Calculate the [SO₃^-2]

2MnO₄^- + 3SO₃^-2 + H₂O -----> 2MnO₂ + 3SO₄^-2 + 2OH^- [SO₃^-2] = 1.88M

20. How is the breathalyzer reaction used to determine BAC? Write the reaction and describe how it works. BAC is blood alcohol concentration which is related to the concentration of alcohol in the breath. The alcohol in a breath sample reacts with Cr₂O₇^-2 reducing the orange color of the solution.

8 H+ + Cr₂O₇^-2 (orange) + 3C₂H₅OH ------> 2Cr⁺³ (green) + 3C₂H₄O + 7H₂O

21. 2H⁺ + Mg-----> Mg⁺² +H₂

Determine the Oxidizing agent H⁺ and the Reducing agent Mg

22. Choose a suitable redox reactant to oxidize Cl^- to ClO₄^- in a redox titration. MnO₄^- in acid

23. Describe as an electrochemical or electrolytic cell:

a) Fuel cell	electrochemical
b) Charging a car battery	electrolytic
c) Discharging a car battery	electrochemical
d) Ni plating	electrolytic
e) Industrial Al production	electrolytic
f) Cl2 production	electrolytic
g) Electrowinning	electrolytic

24) Which of the reactants is gaining electrons? Which of the reactants is the oxidizing agent?

Br₂ (oxidizing agent and is gaining electrons) + SO₂ +Na₂SO₄ +H₂O --------> 2H₂SO₄ + 2NaBr

25) A student studied the following reactions and she recorded:

Pd⁺² + Cu -------> Pd + Cu⁺² spontaneous

Pd⁺² + Au -------> no reaction

Pd⁺² + Hg -------> no reaction

Au⁺³ + Hg -------> Au + Hg⁺² spontaneous

List the oxidizing agents from strongest to weakest. List the reducing agents from strongest to weakest. Predict if the reaction will occur.

Strongest Oxidizing agent	Au^+3 + 3e^- -------> Au
	Hg^+2 + 2e^- -------> Hg
	Pd^+2 + 2e^- -------> Pd
	Cu^+2 + 2e^- -------> Cu	Weakest Reducing Agent

Au⁺³ + Cu ------------> Yes Spontaneous Reaction

26) Match each type of electrolytic cell with the example cell.

Electrowinning	Pure Al is reduced at the cathode from molten bauxite (Al2O3).
Electroplating	A silver anode oxidizes & Ag reduces on a Cu cathode
Electrorefining	Pure Pb is reduced at the cathode while impure Pb oxidizes at the anode

27. List the anode, cathode, anode reaction , cathode reaction, and electrolyte for each commercial electrochemical cell.

Cell	anode	anode reaction	cathode	cathode reaction	electrolyte
Leclanche or Common Dry Cell	Zn	Zn-->Zn+2 + 2e-	C/MnO2	Mn^+4+1e^- -----> Mn^+3	NH4Cl
Alkaline Cell	Zn	Zn-->Zn+2 + 2e-	C/MnO2	Mn^+4+1e^- -----> Mn^+3	KOH
Lead Storage or Car Battery	Pb	Pb ---> Pb^+2+ 2e^-	PbO2	PbO2 + SO4^-2 + 4OH^-1+ 2e^------> PbSO4 + 2H2O	H2SO4
Fuel Cell	C	H2 + 2OH^----> 2H2O + 2e^-	C	O2 + 2H2O +4e^-----> 4OH^-	KOH

28. Which of the above cells requires continuous input of O₂ and H₂ and is produced by Ballard Industries. Fuel Cell

29. List the anode, cathode, anode reaction , cathode reaction, and electrolyte for each commercial electrolytic cell.

Cell	anode	anode reaction	cathode	cathode reaction	electrolyte
Electrolysis of Molten Al2O3	C	O^-2 ---> O2 + 2e^-	C	Al^+3 + 3e^- ---> Al	Molten Al2O3
Electrolysis of Aqueous NaCl	C	2Cl^- ----> Cl2 + 2e^-	C	2H2O + 2e^-----> H2 + 2OH^-	Aqueous NaCl
Silver-plating a Cu spoon	Ag	Ag ---> Ag^+ + 1e^-	Cu	Ag^+ + 1e^- ---> Ag	AgNO3(aq)
Electrorefining pure Pb from impure Pb	Impure Pb	Pb ---> Pb^+2 + 2e^-	Pure Pb	Pb^+2 + 2e^- ---> Pb	PbSiF6

30. Describe each term:

salt bridge	U-tube filled with salt solution connecting two half cells in a electrochemical cell. Allows ions to migrate.
electrolyte	A solution that contains ions and conducts electricity.
anode	Metal electrode that is the site of oxidation.
cathode	Metal electrode that is the site of reduction.
spontaneous	Occurs naturally and has a positive E^o.
electronegativity	The ability to attract electrons.
cation	Positive ion.
anion	Negative ion.
electrochemical cell	Two metals in electrolytes joined by a salt bridge using spontaneous redox reaction to produce an electrical current.
electrolytic cell	A power supply connected to inert electrodes in an electrolyte which forces nonspontaneous redox reactions to occur.
oxidation number	The real or apparent charge of an atom if all bonds are assumed to be ionic.
electrolysis	What occurs in an electrolytic cell.
oxidation	Loss of electrons.
reduction	Gain of electrons.
oxidizing agent	Causes oxidation by undergoing reducing.
reducing agent	Causes reduction by undergoing oxidation.
electrode	Strip of C or Metal used in a cell.
corrosion	The oxidation of a metal often Fe ---> Fe^+2 + 2e^-
electrowinning	The reduction of a metal from its ore by electrolysis.
electrorefining	The purification of a metal by electrolysis.
overpotential effect	The higher than normal voltage for the oxidation and reduction of water.
fuel cell	An electrochemical cell that converts H2 and O2 into H2O and electricity.

31. Define corrosion of a metal, and illustrate your definition with reference to an example, using appropriate equations. Give TWO methods by which corrosion can be prevented and describe how each method works. The two methods must involve different chemical principles.

The corrosion of iron Cathode: Fe ----> Fe⁺² + 2e^-

Anode: O₂ + 2H₂O + 4e^- ------> 4OH^-

1) Painting prevents the reactants: O₂ + 2H₂O from colliding with the surface of the metal.

2) Galvinizing allows Zn to corrode (anode) instead of Fe (cathode) due to the action of the chemical cell they produce.

32. Explain why you would choose Zn or Cu to cathodically protect iron? Zn because it oxidizes more readily than Fe forcing Fe to be the cathode or site of reduction.

33. A⁺² does not react with B, while C⁺² reacts with B. Rank the oxidizing agents in decreasing order of strength. Rank the reducing agents in decreasing order of strength. Will A⁺² react with C?

C⁺² + 2e^- --------> C Oxidizing agents: C⁺² B⁺² A⁺²

B⁺² + 2e^- --------> B Reducing Agents: A B C

A⁺² + 2e- --------> A

A⁺² will not react with C.

34. Write half reactions for each using the reduction table and list the half cell potential.

	Half Reaction	E^o
oxidation of water	H2O --------> 1/2 O2 + 2H^+ + 2e^-	-0.82v
oxidation of water in acid	2 H2O --------> 1/2O2 + 2H^+ + 2e^-	-1.23v
reduction of water	2 H2O + 2e^- ------------> H2 + 2OH^-	-0.41v
reduction of water in alkaline	2 H2O + 2e^- ------------> H2 + 2OH^-	-0.83v
oxidation of H2 in water	H2 + 2OH^-------------> 2 H2O + 2e^-	+0.41
oxidation of H2 in acid	H2 ------------> 2H^+ + 2e^-	0.00v
oxidation of H2 in base	H2 + 2OH^-------------> 2 H2O + 2e^-	+0.83
reduction of Cr2O7^-2 in acid	Cr2O7^-2 + 14 H^+ + 6 e^--------> 2Cr^3+ + 7 H2O	+1.23v
reduction of HBr	2H^+ + 2e^-------------> H2	0.00v

35.Completely analyze the following electrochemical cell.

The anode reaction is:	Zn -----------> Zn^+2+ 2e^-
The cathode reaction is:	Cu^+2 + 2e^- -------> Cu
The electrons flow from ___ to ___	anode to cathode
The ions that migrate to the Zn electrode are:	NO3^-
The ions that migrate to the Cu electrode are:	Zn^+2 Cu^+2K^+
The intial voltage of this cell is:	1.10v
The voltage of this cell once equilibrium is reached is:	0.00v
Describe the change in [Cu^+2] in the Cu half cell	decreases
Describe the change in [NO3^-1] in the Zn half cell	increase

36. Completely analyze the following electrochemical cell.

The anode reaction is:	H2 ------------> 2H^+ + 2e^-
The cathode reaction is:	Cu^+2 + 2e^- -------> Cu
The electrons flow from ___ to ___	anode to cathode
The ions that migrate to the Pt electrode are:	NO3^- Cl^-
The ions that migrate to the Cu electrode are:	Cu^+2 K^+ H^+
The intial voltage of this cell is:	0.34v
The voltage of this cell once equilibrium is reached is:	0.00v
Describe the change in [Cu^+2] in the Cu half cell	decreases
Describe the change in [NO3^-1] in the H^+/H2 half cell	increases

38. Completely analyze the following electrolytic cell. Note that the electrodes are not inert and because of that, the anode might oxidize.

Anode Reaction	Cu ® Cu^2+ + 2e^- E^0 = -0.34 v
Cathode Reaction	2H2O+ 2e^- ® H2 + 2OH^- E^0 = -0.41 v
Chemicals produced at the anode	Cu^2+
Chemicals produced at the cathode	H2 OH^-
The electrons flow from	Anode (right) to cathode (left)
The MTV	+0.75 v
Which electrode is the anode ?	right

38. Completely analyze the following electrolytic cell.

Anode Reaction	2O^-2 ---------> O2 +4e^-
Cathode Reaction	Al^+3 + 3e^- ---------> Al
Chemicals produced at the anode	O2
Chemicals produced at the cathode	Al
The electrons flow from __to __	anode to cathode
The chemical used to lower the mp is:	cryolite
Which electrode is the anode ?	the one on the right

Back to Redox Resource Page