Today s Objectives: Section 13.2 (pp )

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1 1 Today s Objectives: 1. Define oxidizing agent and reducing agent 2. Identify electron transfer, oxidizing agents, and reducing agents in REDOX reactions that occur everyday in both living and non-living systems. Section 13.2 (pp )

2 Redox Terms Review: LEO the lion says GER Loss of electrons = entity being oxidized Gain of electrons = entity being reduced OIL RIG Oxidation is Loss Reduction is Gain Chemists don t usually say

2 2 Redox Terms Review: LEO the lion says GER Loss of electrons = entity being oxidized Gain of electrons = entity being reduced OIL RIG Oxidation is Loss Reduction is Gain Chemists don t usually say the reactant being oxidized or the reactant being reduced Instead they use the terms OXIDIZING AGENT () and REDUCING AGENT () OXIDIZING AGENT: causes oxidation by removing (gaining) electrons from another substance in a redox reaction, therefore the oxidizing agent is being reduced. REDUCING AGENT: causes reduction by donating (losing) electrons to another substance in a redox reaction, therefore the reducing agent is being oxidized. What does this mean? Let s revisit zinc reacting with and hydrochloric acid. Which reactant was reduced? Which was oxidized? Which is the Oxidizing Agent ()? Which is the Reducing Agent () LEO = Oxidized Zn (s) Zn 2+ (aq) + 2 e - Reducing Agent GER = Reduced 2 H + (aq) + 2 e - H 2 (g) Oxidizing Agent

3 Redox Terms Silver ions were reduced to silver metal by reaction with copper metal. Simultaneously, copper metal was oxidized to copper(ii) ions by reaction with silver ions.

3 3 Redox Terms Silver ions were reduced to silver metal by reaction with copper metal. Simultaneously, copper metal was oxidized to copper(ii) ions by reaction with silver ions. If Ag + (aq) is reduced it s the: If Cu (s) is oxidized it is the: OXIDIZING AGENT () REDUCING AGENT () It is important to note that oxidation and reduction are processes, and oxidizing agents and reducing agents are substances.

4 4 Redox Terms Summary so far: The substance that is reduced (gains electrons) is also known as the oxidizing agent The substance that is oxidized (loses electrons) is also knows as the reducing agent Figure 3 p. 569 Question: If a substance is a very strong oxidizing agent, what does this mean in terms of electrons? The substance has a very strong attraction for electrons. Question: If a substance is a very strong reducing agent, what does this mean in terms of electrons? The substance has a weak attraction for its electrons, which are easily removed

5 5 REDOX Reactions so far Reduction Historically, the formation of a metal from its ore (or oxide) i.e. nickel(ii) oxide is reduced by hydrogen gas to nickel metal NiO (s) + H 2(g) Ni (s) + H 2 O (l) Ni +2 Ni o A gain of electrons occurs (so the entity becomes more negative) Electrons are shown as the reactant in the half-reaction A species undergoing reduction will be responsible for the oxidation of another entity, therefore is classified as an oxidizing agent () Oxidation Historically, reactions with oxygen i.e. iron reacts with oxygen to produce iron(iii) oxide 4 Fe (s) + O 2(g) Fe 2 O 3(s) Fe 0 Fe +3 A loss of electrons occurs (so the entity becomes more positive) Electrons are shown as the product in the half-reaction A species undergoing oxidation will be responsible for the reduction of another entity, therefore is classified as an reducing agent ()

6 6 Today s Objectives: 1. Define oxidizing agent, reducing agent, and half-reaction 2. Compare the relative strengths of oxidizing and reducing agents from empirical data. 3. Predict the spontaneity of a REDOX reaction based on a REDOX table, and compare predictions to experimental results. Section 13.2 (pp )

7 7 Quick REDOX Review REDOX reaction explained as a transfer of valence electrons from one substance to another (i.e. two entities involved in e transfer) oxidation & reduction reactions are processes oxidizing & reducing agents are substances loses e (weak attraction) causing reduction by being oxidized (OIL) gains e (strong attraction) causing oxidation by being reduced (RIG) e transfer from to

8 8 REDOX Table Used to indicate the relative strengths of and Consider the reactivity of metal ions in Table 1 p. 569 metal ions () gain elections to oxidize metals () Table 1 p. 569 Ions Ag + (aq) Cu 2+ (aq) Pb 2+ (aq) Zn 2+ (aq) reacted with Cu (s), Pb (s), Zn (s) Pb (s), Zn (s) Zn (s) none number of reactions reactivity order Most Least Based on evidence collected, we can rank the ability of the metal ion to react with the metals. The most reactive metal ion, Ag + (aq), has the greatest tendency to gain electrons, unlike the Zn 2+ (aq), which shows no tendency to gain electrons in the combinations tested.

9 9 REDOX Table By convention, table written as reduction half reactions, therefore all reactants will be (i.e. gain e ) list in decreasing order of strength S Ag + (aq) + e - Ag (s) Cu 2+ (aq) + 2 e - Cu (s) Pb 2+ (aq) + 2 e - Pb (s) Zn 2+ (aq) + 2 e - Zn (s) + n e - S

10 10 REDOX Spontaneity Rule A reaction is considered spontaneous if it occurs on its own The table of relative strengths of and with reduction half reactions is useful in predicting the spontaneity of a reaction Spontaneous REDOX reactions occur only if the is above the If is below the, then the reaction is considered non-spontaneous. A reaction will be spontaneous if on a redox table: above = spont rxn Figure 5 p. 572 above = non-spont rxn

11 11 Example: Building REDOX Tables Consider the following experimental information and add reduction half-reactions to the REDOX table created earlier. Hg 2+ (aq) Cu 2+ (aq) Ag + (aq) Au 3+ (aq) Hg (s) (l) Cu (s) Ag (s) Au (s) S Au 3+ (aq) + 3 e - Au (s) Check p. 7 of the data booklet. Does this ranking order match? S Hg 2+ (aq) + 2 e - Hg (s) Ag + (aq) + e - Ag (s) Cu 2+ (aq) + 2 e - Cu (s) Pb 2+ (aq) + 2 e - Pb (s) Zn 2+ (aq) + 2 e - Zn (s) S YES! Because of the spontaneity rule!

12 12 Sample Problem 13.4 p. 573 The spontaneity rule can also be used to generate REDOX tables Use the following information to create a table of reduction half reactions 3 Co 2+ (aq) + 2 In (s) 2 In 3+ (aq) + 3 Co (s) Pd (s) Cu 2+ (aq) + Co (s) Co 2+ (aq) + Cu (s) Cu 2+ (aq) + Pd (s) no reaction Determine the relative position of REDOX pairs based on reaction spontaneity Cu 2+ Co 2+ Co (s) In (s) Figure 6 p. 573 S Pd 2+ (aq) + 2 e - Pd (s) Cu 2+ (aq) + 2 e - Cu (s) Co 2+ (aq) + 2 e - Co (s) In 3+ (aq) + 3 e - In (s) S

13 Example: Building REDOX Tables Use the following information to create a table of reduction half reactions 2 A 3+ (aq) + 3 D (s) 3 D 2+ (aq) + 2 A (s) A 3+ G + (aq) + D (s) no reaction

13 13 Example: Building REDOX Tables Use the following information to create a table of reduction half reactions 2 A 3+ (aq) + 3 D (s) 3 D 2+ (aq) + 2 A (s) A 3+ G + (aq) + D (s) no reaction D 2+ D (s) 3 D 2+ (aq) + 2 E (s) 3 D (s) + 2 E 3+ (aq) G + (aq) + E (s) no reaction G + E (s) S A 3+ (aq) + 3 e - A (s) D 2+ (aq) + 2 e - D (s) E 3+ (aq) + 3 e - E (s) G + (aq) + e - G (s) S

14 REDOX Tables Trends So far examples include that are metal ions and that are metal atoms. What else could gain or lose electrons? Non-metal atoms gain electrons i.e. Cl 2(g) + 2e 2 Cl (aq) Cl (aq) could act as a Reducing Agent Non-metal ions lose electrons i.

14 14 REDOX Tables Trends So far examples include that are metal ions and that are metal atoms. What else could gain or lose electrons? Non-metal atoms gain electrons i.e. Cl 2(g) + 2e 2 Cl (aq) Cl (aq) could act as a Reducing Agent Non-metal ions lose electrons i.e. 2 Br (aq) Br 2(l) + 2 e Br 2(l) could act as an Oxidizing Agent tend to be metal ions and non-metal atoms tend to be metal atoms and non-metal ions Are there any entities that could act as both or? Multivalent metals p. 574

15 15 Homework Practice Qs p. 571 #1-10 Lab Exercise 13.A p. 572 DUE: Thursday, October 29 Practice Qs p. 573 #11-14; p. 574 #15-24

16 16 Today s Objectives: 1. Predict REDOX reactions 2. Define disproportionation 3. Identify electron transfer, oxidizing agents, and reducing agents in REDOX reactions that occur everyday in both living and non-living systems. Section 13.2 (pp )

17 17 Practice Question - p. 573 #14 Use the following information to create a table of reduction half reactions Ag (s) + Br 2(l) AgBr (s) Ag (s) + I 2(s) no evidence of reaction Br 2(l) Cl (aq) Ag (s) Cu 2+ (aq) + I (aq) no redox reaction I 2(s) I (aq) Br 2(l) + Cl (aq) no evidence of reaction Cu 2+ (aq) S Cl 2(g) + 2 e 2Cl (aq) Br 2(l) + 2 e 2Br (aq) Ag + (aq) + 1 e Ag (s) I 2(s) + 2 e 2I (aq) Cu 2+ (aq) + 2 e Cu (s) S

18 18 Predicting REDOX Reactions With the knowledge of REDOX reactions you will be responsible for determining if a reaction will spontaneously occur and its corresponding reaction equation. 1. List all the entities that are present Refer to Table 6 p. 575 In solutions, molecules and ions behave independently of each other. Example: copper metal placed into an acidic solution of potassium permanganate Cu (s) K + (aq) MnO 4 (aq) H + (aq) H 2 O (l)

19 19 Predicting REDOX Reactions 2. Determine all possible and This is a crucial step!! Consider: Combinations MnO 4 - (aq) is only an in an acidic solution Indicate this pair by drawing an arc between the permanganate and hydrogen ion Species that can act as or Label both possibilities in your list Cu (s) K + (aq) MnO 4 (aq) H + (aq) H 2 O (l)

20 20 Predicting REDOX Reactions 3. Identify the S and S using the REDOX table in the data booklet Predict the reaction spontaneity S Cu (s) K + (aq) MnO 4 (aq) H + (aq) H 2 O (l) S S > S spont. 4. Show the reduction half reactions and balance Copy the S equation directly from table Read the S equation from right to left 2 [ ] MnO 4 (aq) + 8H + (aq) + 5e Mn 2+ (aq) + H 2 O (l) 5 [ Cu (s) Cu 2+ (aq) + 2e ] spont. 2 MnO 4 (aq) + 16H + (aq) + 5Cu (s) 2Mn 2+ (aq) + 2H 2 O (l) + 5Cu 2+ (aq)

21 21 Sample Problem 13.5 p. 576 potassium permanganate solution is slowly poured into acidified iron(ii) sulfate solution S Figure 9 p. 576 S spont. Experimentally when these solutions are mixed the purple color of the permanganate ion disappears as it is reacted. Also a diagnostic test of the ph would indicate hydrogen ions reacting if the ph increased.

22 22 Communication Example 1 p. 577 Could copper pipe be used to transport a hydrochloric acid solution? Figure 10 p. 577 Since the reaction is nonspontaneous, it should be possible to use a copper pipe to carry hydrochloric acid.

23 23 Disproportionation The REDOX electron transfer reactions covered so far have one reactant () that removes electrons from a second reactant () if a spontaneous reaction occurs. Although the and are usually different entities, this is not a requirement. A reaction is which a species is both oxidized and reduced is called disproportionation aka autoxidation or self oxidation-reduction occurs when a substance can act as either an or

24 24 Disproportionation Example: Will a spontaneous reaction occur as a result of an electron transfer from one iron(ii) ion to another iron (II) ion when two iron (II) solutions are combined? non spont. Use the REDOX table and spontaneity rule, which indicates that iron(ii) as an is below iron(ii) as a, therefore the reaction is non-spontaneous and will not occur.

25 Disproportionation Example: Will a spontaneous reaction occur as a result of an electron transfer from one copper(i) ion to another copper (I) ion?

25 25 Disproportionation Example: Will a spontaneous reaction occur as a result of an electron transfer from one copper(i) ion to another copper (I) ion? Cu + (aq) + 1 e - Cu (s) Cu + (aq) Cu 2+ (aq) + 1 e - 2 Cu + (aq) Cu 2+ (aq) + Cu (s) spont. Use the REDOX table and spontaneity rule, which indicates that copper (I) as an is above copper (I) as a, therefore an aqueous solution of copper (I) ions will spontaneously, but slowly, disproportionate into copper (II) ions and copper metal. Communication Examples 2 p. 578

26 26 Predicting REDOX Reactions by Constructing Half-Reactions Suppose the REDOX table does not provide the half-reaction equations needed Use your knowledge about constructing half-reactions to create a REDOX equation Recall the summary on page 567 for writing half-reaction equations. Consider the main starting materials and reaction conditions (acidic or alkaline) Create a skeleton equation showing only the main reactants and products Examine individual balanced half-reaction equations to determine the details of the overall REDOX reaction equation

27 27 Sample Problem 13.6 p. 580 A person suspected of being intoxicated uses a breathalyzer device and the alcohol in their breath reacts with an acidic dichromate ion solution to produce acetic acid (ethanoic acid) and aqueous chromium(iii) ions. Predict the balanced REDOX reaction equation. Create a skeleton equation from the information provided: Separate the entities into the start of two half-reaction equations Apply strategies for writing half reactions (p. 567) Now, balance the electrons lost and gained, and add the half reactions. Cancel the electrons and anything else that is exactly the same on both sides of the equation.

28 28 Communication Example 3 p. 581 Permanganate ions and oxalate ions react in a basic solution to produce carbon dioxide and manganese (IV) oxide Create a skeleton equation from the information provided: Separate the entities into the start of two half-reaction equations Apply strategies for writing half reactions (p. 567) Now, balance the electrons lost and gained, and add the half reactions. Cancel the electrons and anything else that is exactly the same on both sides of the equation. Basic solution so add OH - (aq) to both sides to equal the number of H + (aq) present. Cancel equal amounts of H 2 O (l) from both sides.

29 29 Summary Predicting REDOX Reactions by Constructing Half-Reaction Equations p Use the information provided to start two half-reaction equations. 2. Balance each half-reaction equation. 3. Multiply each half-reaction by simple whole numbers to balance electrons lost and gained. 4. Add the two half-reaction equations, cancelling the electrons and anything else that is exactly the same on both sides of the equation.

30 30 REDOX in Living Organisms The smell of a skunk is caused by a thiol compound (R-SH). To deodorize a pet sprayed by a skunk, you need to convert the smelly thiol to an odourless compound. Hydrogen peroxide in a basic solution (usually sodium bicarbonate) acts as an oxidizing agent to change the thiol to a disulfide compound (RS-SR), which is odourless. Figure 8 p. 575

31 31 Investigation 13.3 p. 581 Predict the products of the reaction of sodium metal with water. S Na (s) S H 2 O (l) VIDEOS: 2 H 2 O (l) + 2 e H 2(g) + 2 OH (aq) 2 [ Na (s) Na + (aq) + e ] 2 H 2 O (l) + 2 Na (s) 2 Na + (aq) + H 2(g) + 2 OH (aq) Brainiacs! spont. Slow Motion Diagnostic Test? Na in Water Na Properties Determine presence with the hydrogen pop test Cesium Examine ph for an alkaline solution

32 32 Homework Practice Qs p. 575 #25; p. 579 #25-30; p. 579 #26-30; p. 581 #31-33 Section 13.2 Review p. 582 #1-18 Section 13.2 Extra Exercises handout

Today s Objectives: Section 13.3 (pg )

Today s Objectives: Section 13.3 (pg ) 1 Today s Objectives: 1. Define oxidation number 2. Write and balance equations for REDOX reactions in acidic, basic, and neutral solutions with half-reaction equations, developing simple half-reaction