Ch.4 - Chemical Quantities & Aqueous ReactionsSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Oxidation and reduction deals with the transferring of electrons between reactants. The reactant that loses electrons is oxidized, while the reactant that gains electrons is reduced

Redox Reactions

Concept #1: Understanding Oxidation versus Reduction

When in doubt about oxidation or reduction just remember the phrase: "LEO the lion goes GER."

Concept #2: Rules for Oxidation Numbers 

We use these oxidation number rules whenever we are asked to determine the oxidation number of an entire compound or the individual elements within a compound. 

Example #1: What is the oxidation number of each underlined element? 

Instead of being asked who is oxidized or reduced, sometimes you may be asked to determine the reducing and oxidizing agents

Example #2: In the following reaction identify the oxidizing agent and the reducing agent

Try your skills at determing the oxidation number of elements within molecules or polyatomic ions. 

Practice: What is the oxidation number of each underlined element?

a) P4                                  b) BO33–                                c) AsO42–                           d) HSO4

Just remember if you've been oxidized then you're the reducing agent and if you've been reduced then you're the oxidizing agent.

Practice: In the following reaction identify the oxidizing agent and the reducing agent:

Cr2O72- + 6 Fe2+ + 14 H→ 2 Cr3+ + 6 Fe3+ + 7 H2O

Basic Redox Concepts

Concept #3: OXIDATION-REDUCTION (REDOX) reactions deal with the transfer of electrons from one reaction to another.

Concept #4: From our understanding of redox reactions we can draw connections to voltage, current, charge and power. 

Additional Problems
Which of these ions is the best reducing agent?  Standard Reduction Potentials                   E°      Fe 3+ (aq) + e– → Fe 2+ (aq)                + 0.77 V Cu 2+ (aq) + e– → Cu + (aq)                 + 0.15 V   a) Fe 3+ b) Fe 2+ c) Cu 2+ d) Cu +    
Of the substances below, which is the weakest reducing agent? a. Na (s) b. K+ (aq) c. Cl2 (g) d. Br - (aq) e. Fe2+ (aq)
Given the overall redox reaction:  Fe2+(aq) + Ce4+(aq) → Fe3+(aq) + Ce3+(aq) Identify the two half-reactions Oxidation half-reaction                            Reduction half-reaction A) Fe2+(aq) → Fe3+(aq) + e−                     Ce4+(aq) + e− → Ce3+(aq) B) Ce4+(aq) + e− → Ce3+(aq)                    Fe2+(aq) → Fe3+(aq) + e− C) Fe2+(aq) + e− → Fe3+(aq)                     Ce4+(aq) → Ce3+(aq) + e− D) Ce4+(aq) → Ce3+(aq) + e−                    Fe2+(aq) + e− → Fe3+(aq) E) Fe3+(aq) →Fe2+(aq) + e−                      Ce4+(aq) → Ce3+(aq) + e−
Which of the following is the strongest reducing agent?                                                                E° Sn2+(aq) + 2e- → Sn°                             -0.14 Cr3+(aq) + 3e- → Cr°                             -0.73 Sn4+(aq) + 4e- → Sn2+(aq)                     +0.15 Mn2+(aq)+ 2e- → Mn°                            -1.18 Cr2+(aq) + 2e- → Cr°                              -0.23 A) Sn2+(aq) B) Mn2+(aq) C) Sn4+(aq) D) Cr2+(aq) E) Mn°(aq)  
Use the standard reduction potentials below to determine which element or ion is the best reducing agent. Pd2+ (aq) + 2 e –       →      Pd (s) E° = + 0.90 V 2 H+ (aq) + 2 e –        →        H2 (g) E° = 0.00 V Mn2+ (aq) + 2 e –       →      Mn (s) E° = – 1.18 V   a) Pd (s)             b) H + (aq)              c) Mn2+ (aq)              d) H2 (g)
Consider the following standard reduction potentials in acid solution:                                                             E°(V) Al3+ + 3e- → Al(s)                                - 1.66 AgBr(s) + e- → Ag(s) + Br -                   + 0.07 Sn4+ + 2e- → Sn2+                              + 0.14 Fe3+ + e- → Fe2+                                 + 0.77 The strongest oxidizing agent among those shown above is  A) Fe3+. B) Fe2+. C) Br -. D) Al3+. E) Al.
Which of the following is the weakest oxidizing agent?                                                                      E° Sn2+ + 2e- → Sn°                                      -0.14 Cr3+ + 3e- → Cr°                                       -0.73 Sn4+ + 4e- → Sn2+                                    +0.15 Mn2+ + 2e- → Mn°                                     -1.18 Cr2+ + 2e- → Cr°                                       -0.23 A) Sn2+(aq) B) Mn2+(aq) C) Sn4+(aq) D) Cr2+(aq) E) Cr3+(aq)
Identify the oxidation and reduction steps in the following reaction: 4Fe +3O2 → 2Fe2O3  
When designing a voltaic cell with the following cell notation:                         Li(s) | Li+(aq) ‖ Zn2+(aq) | Zn(s) That uses a salt bridge made of NaCl, what answer describes what is occurring at the anode? A.  Lithium is being oxidized and Cl − joins the solution B.  Lithium is being reduced and Cl − joins the solution C.  Zinc is being oxidized and Cl− joins the solution D.  Zinc is being oxidized and Na+ joins the solution E.  Lithium is being oxidized and Na+ joins the solution
Rank these species by their ability to act as an oxidizing agent.  Au3+, Ca2+, Pb2+, Fe2+
Which of the following chemical species is the strongest reducing agent based on the following information:F2(g) + 2 e – → 2 F– (aq)           E°cell = +2.87 VMg2+ (aq) + 2 e – → 2 Mg (s)     E° cell = –2.37 V a) F2 (g)b) Mg2+ (aq)c) F– (aq)d) Mg (s)e) None of the above
Rank these species by their ability to act as an oxidizing agent from Best oxidizing agent to least oxidizing agent. Al3+, Au3+, Fe2+, Cu+
Break down reaction into its half-reactions.4Fe + 3O2 → 2Fe2O3
Rank the following half reactions (1-5) in order of oxidizing ability, from strongest to weakest._______   K → K+ + e–                                 E° = + 2.93 V _______   F2 + 2 e– → 2 F –                         E° = + 3.0 V________  2 H2O + 2 e– → H2 + 2 OH–       E° = – 0.83 V ________  Ag → Ag+ + e–                            E° = – 0.80 V ________  Ni2+ + 2 e– → Ni                         E° = – 0.23 V
What is the net cell reaction for the chromium-silver voltaic cell?Cr(s) → Cr3+(aq) + 3e-Ag+(aq) + e- → Ag(s) 
Which of the following metal cations is the best oxidizing agent?a. Cu+b. Zn2+c. Cd2+d. Cr3+ 
Which of the following metals is the best reducing agent?a. Crb. Mnc. Nid. Li
Consider the following standard reduction potentials:Al3+ + 3e –  → Al (s)                  E ̊red = –1.66AgBr (s) + e – → Ag (s) + Br–    E ̊red = +0.07Sn4+ + 2e – → Sn2+                  E ̊red = +0.14Fe3+ + e – → Fe2+                     E ̊red = +0.77Which of the following substances below is the strongest reducing agent?a) Fe3+b) Fe2+c) Ag (s)d) Al3+e) Al (s)
Which substance below is the strongest reducing agent? See the attached table of standard reduction potentials.a) Li+ (aq)b) Li (s)c) F– (aq)d) F2 (g)e) H2 (g)
Which of the following metal cations is the best oxidizing agent?a. Co+2b. Zn+2c. Fe+2d. Fe+3
Of the substances below, which is the weakest reducing agent? a) Na (s) b) K+ (aq) c) Cl2 (g) d) Br– (aq) e) Fe2+ (aq)
Indicate the half-reaction occurring at Anode, and Cathode.2Ag+(aq) + Pb(s) → 2Ag(s) + Pb 2+(aq)
Separate this redox reaction into its component half-reactions. O2 + 2Mg → 2MgO
Write a balanced overall reaction from these unbalanced half-reactions.i) In → In3+ii) Cd2+ → Cd
For the reaction:Ni2+(aq) + Mg(s) → Ni(s) + Mg 2+(aq)a. Indicate the half-reaction occurring at Anode.b. Indicate the half-reaction occurring at Cathode.Express your answer as a chemical equation. Identify all of the phases in your answer.
Two metals are represented by the symbols L and Z. Which is the best oxidizing agent listed?(A) L(B) L2+(C) Z(D) Z+
Separate this redox reaction into its component half-reactionsCl2 + 2Cs → 2CsClOxidation half reaction:Reduction half reaction:
Separate this redox reaction into its balanced component half-reactions.Cl2 + 2Cu → 2CuClOxidation half-reaction:Reduction half-reaction:
For the oxidation-reduction reaction equation given below, indicate how many electrons are transferred in the formation of one formula unit of product.2Na + S → Na 2S 
Separate this redox reaction into its component half-reactions. O2 + 2Cu → 2CuO
Which of the following substances is the strongest oxidizing agent given the standard reduction potential? A. +2.71B. +0.40C. 0.00D. -0.81
Separate this redox reaction into its component half-reactions. 3O2 + 4Co → 2Co 2O3 
Identify the oxidation and reduction steps in the following reaction:4 Fe + 3 O2 → 2 Fe2O3 
Which of the following is the STRONGEST reducing agent?a. Ba(s)b. Li+ (aq)c. Na(s)d. Cr2+ (aq)e. Li(s)
Predict the relative reducing power of the group 2A elements. Rank from strongest to weakest reducing agent. To rank items as equivalent, overlap them.Ca, Mg, Be, Sr, Ba
Given the overall redox reaction: Fe2+(aq) + Ce4+(aq) → Fe3+(aq) + Ce3+(aq)  Identify the two half-reactions. Oxidation half-reaction                          Reduction half-reactionA) Fe 2+(aq) → Fe 3+(aq) + e−              Ce 4+(aq) + e − → Ce 3+(aq)B) Ce 4+(aq) + e − → Ce 3+(aq)           Fe 2+(aq) → Fe 3+(aq) + e −C) Fe 2+(aq) + e − → Fe 3+(aq)           Ce 4+(aq) → Ce 3+(aq) + e −D) Ce 4+(aq) → Ce 3+(aq) + e −           Fe 2+(aq) + e − → Fe 3+(aq)E) Fe 3+(aq) →Fe 2+(aq) + e −              Ce 4+(aq) → Ce 3+ (aq) + e −
2NO3-(aq) + 8H+(aq) + 3Cu(s) → 2NO(g) + 4H 2O(l) + 3Cu2+(aq) i)  Indicate the half-reaction occurring at Anode. Express your answer as a chemical equation. Identify all of the phases in your answer.     ii) Indicate the half-reaction occurring at Cathode. Express your answer as a chemical equation. Identify all of the phases in your answer.
Which metal cation is the best oxidizing agent?a. Pb2+b. Cr3+c. Fe2+d. Sn2+
Rank these species by their ability to act as an oxidizing agent. Cu+, Cr2+,Cl2, Na+ Rank from best oxidizing agent to poorest oxidizing agent.
Rank these species by their ability to act as an oxidizing agent. Mg2+, Zn2+, Cu+, F2
Rank these species by their ability to act as an oxidizing agent. Mg2+, Zn2+, Sn2+, Ag+
Rank these species by their ability to act as an oxidizing agent (from best oxidizing agent to poorest). Ag+, I2, Ca2+, Cr3+
Rank these species by their ability to act as an oxidizing agent. Sn2+, Cr3+, Li+, Ag+
Indicate the half-reaction occurring at Anode and the half-reaction occurring at Cathode of the following: a. Ni2+(aq)+Mg(s) → Ni(s)+Mg2+(aq)b. 2H+(aq)+Fe(s) → H2(g)+Fe2+(aq)c. 2NO3-(aq)+8H+(aq)+3Cu(s) → 2NO(g)+4H2O(l)+3Cu2+(aq)
Based on the data presented below, which is the strongest reducing agent? (a) Fe3+ (b) Fe2+ (c) Br- (d) Al3- (e) AI (s)
2I- + Cl2 → I2 + 2Cl-In the above redox reaction, use oxidation numbers to identify the element oxidized, the element reduced, the oxidizing agent and the reducing agent.
Cr3+ + 3Cu+ → 3Cu2+ + CrIn the above redox reaction, use oxidation numbers to identify the element oxidized, the element reduced, the oxidizing agent and the reducing agent. 
Ag2O + Cu + H2O → 2Ag + Cu(OH)2In the above redox reaction, use oxidation numbers to identify the element oxidized, the element reduced, the oxidizing agent and the reducing agent.
Study this chemical reaction: Pt + O2 → PtO2 Then, write balanced half-reactions describing the oxidation and reduction that happen in this reaction.
Which of the following is the  weakest oxidizing agent?