Unit 12: Redox Class Packet



+03021490034988506239260038103663315004241220503215400Oxidation Numbers ReviewOxidation numbers are very important in this chapter “Redox Reactions.” Without the complete understanding of how to assign these numbers, we cannot move ahead with this chapter. They are much like ionic charges, except that every element will be assigned a number. The most important rules that cannot be broken are:Free elements are zero.Group 1 is +1Group 2 is +2Fluorine is -1Assign oxidation numbers to each element in the following:NaClNa___Cl___H2SH___S___H2OH___O ___CO2C ___O___H2SO4H ___S___ O___FeCO3Fe___C___ O___AgIAg___I___H2H___PbCl2Pb___Cl___BaCO3Ba___C ___ O___Fe2O3Fe___O___I2I____BeOBe____O____CaF2Ca____F ____FeCl3Fe____Cl____PF5P____F____H3PO4H____P____ O___KClK ____Cl____K2OK ____O____O3O ____LiHLi ____H____HBrH ____Br____Li+Li____PO43-P____O___CaH2Ca___H___ Cr2O3Cr___O___ KClO K___Cl___ O___KClO2K___Cl___ O___KClO3K___Cl___ O___KClO4K___Cl___ O___Na2SO4Na___S___ O___Ca(OH)2Ca___O___ H___Na2CO3Na___C___ O___B2(Cr2O7)3B___Cr___ O___Al2(SO4)3Al___S___ O___Al(NO3)3Al___N___ O___(NH4)3PO4 N___H___ P___ O____REDOX Reactions ReviewA redox reaction is a reaction in which electrons are transferred from one element to another. The reaction involves at least two elements, one that will give up an electron, and one that will receive that electron. The term redox comes from two words, “oxidation” and “reduction.” If something is oxidized, it “burns” in oxygen, as shown below:Mg + O Mg+2 + O-2Take a moment to write out their Lewis dot structures. As you can see, Mg is being oxidized and it loses its two valence electrons, while oxygen gains them. Oxidation is defined as the loss of electrons. Considering the name of this reaction, if something is being oxidized, the other element must be reducing. Neither reduction nor oxidation can happen alone. That means that oxygen, in this example, is being reduced because it gains the electrons. Reduction is defined as the gain of electrons. A simple way to remember this is to remember that LEO the lion goes GER. LEO = loss of electrons is oxidation. GER = gain of electrons is reduction. Also, Mg and O are “free” elements, which means their oxidation numbers are both 0. Now you can see that if and element’s oxidation number increases, that element is being oxidized. If an element’s oxidation number decreases it is being reduced (the number is reducing).EXAMPLES: Indicate which element is being oxidized, and which is being reduced.Cu2O Cu + O2Cl2 + KBr KCl + Br2CH4 + O2 CO2 + H2ORedox reactions are usually synthesis reactions, decomposition, combustion or single replacement reactions. Double replacement and neutralization reactions are NOT redox reactions. Usually they are easy to spot because if an element goes from being “free” (with an oxidation number of 0) to being in a compound (with a new oxidation number) it shows there was an exchange of electrons. In the following examples, identify what type of reaction they are and then state if they are redox reactions.N2 + O2 2NO_____________________________________Cl2 + 2NaBr NaCl + Br2_____________________________________2NaOH + HCl H2O + NaCl_____________________________________Redox Half Reactions ReviewA half reaction shows either the oxidation or reduction portion of a redox equation including if the electrons are gained or lost. A reduction half reaction shows an atom or ion gaining one of more e-:Fe3+ + 3e- FeNotice that the e- is on the left.An oxidation half reaction shows an atom or ion losing one or more e-:Mg Mg2+ + 2 e-Notice that the e- is on the right.In a half reaction, only one element is shown and the charges must be conserved. To write a half reaction, first assign all the oxidation numbers to all the elements. Second, cross out any elements that are spectators (they do not change oxidation number). Then, write a half reaction showing a change in oxidation state and label which element is being oxidized and which is being reduced. Last, add in the number of electrons needed to conserve the charge.For the following examples, determine if they represent oxidation or reduction.e- + Cr+3 Cr+22e- + Mn+7 Mn+5Mg+2 + 2e- MgK e- + K+1For the following examples, add in the e- to balance the charge. Cr+5 Cr+2 Mn+4 Mn+7 Cu+1 Cu+2 B+3 B For the following examples, balance the elements first, then add in the e- to balance the charge. Cl- Cl2 Br2 Br-1 I2 I- N+3 N2 S8 S-2 O-2 O2Spontaneous Reactions and Activity SeriesUse Table J to help you with the following questions.Write the oxidation and reduction half reaction for:Ca + Cu2+ Ca2+ + CuAccording to Table J, the element higher on the list will oxidize. Which element is oxidizing here and does that mean that this reaction is spontaneous?Write the oxidation and reduction half reaction forMg + Ca2+ Mg2+ + CaWhich element is oxidizing in number 3 and is the reaction spontaneous?Which of the following ions is most easily oxidized?F-b. Cl-c. Br-d. I-Which element is more easily reduced?Cub. Mgc. Ald. ZnWhich element will reduce Mg2+ to Mg?Feb. Bac. Pbd. AgWhich ion will oxidize Fe?Zn2+b. Ca2+c. Mg2+d. Cu2+Which metal will react spontaneously with Ag+ but not Zn2+?Cub. Auc. Ald. MgWhich reaction will take place spontaneously?Mg + Ca2+ Mg2+ + CaBa + 2Na+ Ba2+ + 2NaCl2 + 2F- 2Cl- +F2I2 + 2Br- 2I- + Br2RedOx Reaction Regents Review 1. Which reaction is an example of an oxidation- reduction reaction?AgNO3 + KI → AgI + KNO3Cu + 2AgNO3 → Cu(NO3)2 + 2Ag2KOH + H2SO4 → K2SO4 + 2H2OBa(OH)2 + 2HCl → BaCl2 + 2H2O2. In an oxidation-reduction reaction, reduction is defined as the (1) loss of protons???? (3) loss of electrons (2) gain of protons???? (4) gain of electrons3. When a lithium atom forms a Li+ ion, the lithium atomgains a proton(3) loses a protongains an electron(4) loses an electron4. Which type of reaction occurs when nonmetal atoms become negative nonmetal ions?oxidation(3) substitutionreduction(4) condensation5. When a neutral atom undergoes oxidation, the atom’s oxidation statedecreases as it gains electronsdecreases as it loses electronsincreases as it gains electronsincreases as it loses electrons6. In a redox reaction, there is a conservation ofmass, onlyboth mass and chargeneither mass nor charge7. In any redox reaction, the substance that undergoes reduction will(1) lose e- & have a decrease in oxidation number(2) lose e- & have an increase in oxidation number(3) gain e- & have a decrease in oxidation number(4) gain e- & have an increase in oxidation number8. What occurs during the reaction below?The manganese is reduced and its oxidation number changes from +4 to +2.The manganese is oxidized and its oxidation number changes from +4 to +2.The manganese is reduced and its oxidation number changes from +2 to +4.The manganese is oxidized and its oxidation number changes from +2 to +4.9. Given the balanced equation:What is the total number of moles of electrons lost by 2 moles of Al(s)?1 mole(3) 3 moles(2) 6 moles(4) 9 moles10. Given the balanced equation:Mg(s)?+ Ni2+(aq)? Mg2+(aq)?+ Ni(s)What is the total number of moles of electrons lost by 2 moles of Mg(s)?(1) 1.0 mol?? (3) 3.0 mol(2) 2.0 mol?(4) 4.0 mol11. Given the equation representing a reaction:Mg(s)?+ Ni2+(aq)? Mg2+(aq)?+ Ni(s)What is the total number of moles of e- lost by Mg when 2.0 moles of e- are gained by Ni2+(aq)?(1) 1.0 mol?? (3) 3.0 mol(2) 2.0 mol?(4) 4.0 mol12. Given the reaction:Which species undergoes oxidation?Mg(s)(3) Cl–(aq)H+(aq)(4) H2(g)13.Given the redox reaction:As the reaction takes place, there is a transfer ofelectrons from Al to Cr3+electrons from Cr3+ to Alprotons from Al to Cr3+(4) protons from Cr3+ to Al17. Given the redox reaction:2 Fe3+ + 3 Zn 2 Fe + 3 Zn2+As the reaction takes place, there is a transfer of electronsfrom Fe3+ to Znfrom Zn to Fe3+ from Zn2+ to Fe(4) from Fe to Zn2+14. Which half-reaction correctly represents oxidation?Fe(s) → Fe2+(aq) + 2e–Fe2+(aq) → Fe(s) + 2e–Fe(s) + 2e– → Fe2+(aq)Fe2+(aq) + 2e– → Fe(s)15. Which equation shows a conservation of both mass and charge?Cl2 + Br– → Cl– + Br2Cu + 2Ag+ → Cu2+ + Ag+Zn + Cr3+ → Zn2+ + CrNi + Pb2+ → Ni2+ + Pb16. Given the balanced ionic equation:Which equation represents the oxidation half-reaction?Zn(s) + 2e– → Zn2+(aq)Zn(s) → Zn2+(aq) + 2e– Cu2+(aq) → Cu(s) + 2e–Cu2+(aq) + 2e– → Cu(s)18.Which half-reaction equation represents the reduction of a potassium ion?(1) K+?+ e–?? K??? (3) K+? K + e–?(2) K + e–? K+??? (4) K K+?+ e–19.Given the equation:The reduction half-reaction isAl → Al3+ + 3e–Cu2+ + 2e– → CuAl + 3e– → Al3+ Cu2+ → Cu + 2e–Iron is a more active metal.+2 for carbon in CO and +4 for carbon in CO20. A flashlight can be powered by a rechargeable nickel-cadmium battery. The unbalanced equation below represents the reaction that occurs as the battery produces electricity. When a nickel-cadmium battery is recharged, the reverse reaction occurs.Balance the equation above using the smallest whole-number coefficients. 1,1,2,1,1Determine the change in oxidation number for Cd. From 0 to +2`1Explain why Cd would be above Ni if placed on Table J. Cd is more reactive than Ni.Voltaic Cells Modeling ActivityDirections: Using table J and your knowledge of atoms, ions, and redox, draw and explain how electrons are transferred and mass changes in the following cell. Draw Bohr diagrams in the zoomed in circles to show charge and mass transfers in more detail. 3982085106680Explain your diagram. Label the anode, cathode, charges, and direction of electron flow. 00Explain your diagram. Label the anode, cathode, charges, and direction of electron flow. 29527503857625001514475376364573342537636452990850385889534766253458845347662534588443905253382645-1047753382644-30480020327334290002368552889809924667406512827Voltaic Cells PracticeDirections: In each of the following, determine which element oxidized easier on table J. Then label the anode, cathode, direction of e- flow, and the half reactions. 2. 3. 4. Additional Questions:On diagram 1, which way will anions travel through the salt bridge?____________On diagram 2, towards which electrode will cations travel through the salt bridge?____________On diagram 3, how many e- are exchanged per mole of Mg?____________On diagram 4, how many e- are transferred between Ag and Ni?____________On all diagrams, at which electrode does oxidation occur?____________On all diagrams, at which electrode does reduction occur?____________On all diagrams, from which electrode will electrons travel? ____________What is the purpose of the salt bridge? ____________________________________________________Describe the change in energy that occurs in voltaic cells in terms of electric and chemical energies:Voltaic Cells Short AnswerAnswer questions 1 and 2 using the diagram below, which represents an electrochemical cell.23863421235611. When the switch is closed, in which half-cell does oxidation occur? 2. What occurs when the switch is closed?(1) Zn is reduced.(2) Cu is oxidized.(3) Electrons flow from Cu to Zn.(4) Electrons flow from Zn to Cu.001. When the switch is closed, in which half-cell does oxidation occur? 2. What occurs when the switch is closed?(1) Zn is reduced.(2) Cu is oxidized.(3) Electrons flow from Cu to Zn.(4) Electrons flow from Zn to Cu.350520126365003. Base your answers to the following questions on the diagram of the voltaic cell below.1327158128000(a) Identify the anode and the cathode. Anode = PbCathode = Ag(b) Write the oxidation and reduction half-reactions for this voltaic cell. Red: 2Ag+ + 2 e- 2Ag2 e-(c) What is the total number of moles of electrons needed to completely reduce 6 moles of Ag+(aq) ions? (d) Describe the direction of electron flow between the electrodes.Electrons flow from the Pb electrode to the Ag electrode(e) State the purpose of the salt bridge in this cell. Maintains a balance of charge; allows ions to migrate(f) State the electrode to which positive ions migrate when the switch is closed. Ag electrode (the cathode) – to balanced the electrons that are arriving (g) As this voltaic cell operates, the mass of the Ag(s) electrode increases. Explain, in terms of silver ions and silver atoms, why this increase in mass occurs.At the Ag electrode, silver ions in the water are being reduced to solid silver atoms. The solid silver deposits on the Ag electrode, which increases its mass.4. Base your answers to the following questions on the diagram below, which represents a voltaic cell at 298 K and 1 atm.015367000In which half-cell will oxidation occur when switch S is closed? Zn, anode, rightWrite the balanced half-reaction equation that will occur in half-cell 1 when switch S is closed. Pb2+ + 2e– Describe the direction of electron flow between the electrodes when switch S is closed. 5. Base your answers to the following questions on the information below.Underground iron pipes in contact with moist soil are likely to corrode. This corrosion can be prevented by applying the principles of electrochemistry. Connecting an iron pipe to a magnesium block with a wire creates an electrochemical cell. The magnesium block acts as the anode and the iron pipe acts as the cathode. A diagram of this system is shown below.01905000(a) State the direction of the flow of electrons between the electrodes in this cell.From Mg (anode) to Fe (cathode) (b) Explain, in terms of reactivity, why magnesium is preferred over zinc to protect underground iron pipes. Your response must include both magnesium and zinc. 6. Base your answers to the following questions on the diagram of a voltaic cell and the balanced ionic equation below.0000What is the total number of moles of electrons needed to completely reduce 6.0 moles of Ni2+(aq) ions? 12Identify one metal from Reference Table J that is more easily oxidized than Mg(s). Explain the function of the salt bridge in the voltaic cell.Electrolytic Cells Modeling ActivityDirections: Using table J and your knowledge of atoms, ions, and redox, draw and explain how electrons are transferred and mass changes in the following cells. Draw Bohr diagrams in the zoomed in circles to show charge and mass transfers in more detail. 3887470339090Explain your diagram. Label the anode, cathode, charges, and direction of electron flow. 00Explain your diagram. Label the anode, cathode, charges, and direction of electron flow. 7673012703416001250727113952599690250507521812253095625021812243095625022574254333875265747525050744781550431482550145495841Electrolytic Cells Practice23145751892301. Which element is oxidizing in the diagram to the left?2. According to E Tables, should that element oxidize? 3. Is this reaction spontaneous?4. What type of cell is it?5. Label the anode and the cathode with charges on the diagram to the left.6. Write the overall reaction for this cell. 001. Which element is oxidizing in the diagram to the left?2. According to E Tables, should that element oxidize? 3. Is this reaction spontaneous?4. What type of cell is it?5. Label the anode and the cathode with charges on the diagram to the left.6. Write the overall reaction for this cell. 57150292097. Water is being decomposed using a battery in the diagram to the right. Write the equation for the decomposition of water.8. Which element is being oxidized? 9. How many e- are lost? 10. Should that element oxidize? 11. Is this reaction spontaneous?12. What type of cell is it?13. Label where oxidation and reduction on the diagram.14. Why is more H2 gas being formed that O2 gas?15. Write a half reaction for Hydrogen.007. Water is being decomposed using a battery in the diagram to the right. Write the equation for the decomposition of water.8. Which element is being oxidized? 9. How many e- are lost? 10. Should that element oxidize? 11. Is this reaction spontaneous?12. What type of cell is it?13. Label where oxidation and reduction on the diagram.14. Why is more H2 gas being formed that O2 gas?15. Write a half reaction for Hydrogen.204298835598616. Only one element is being used in the diagram to the left. The silver plate ionizes and the ions attach to the spoon. Show a half reaction for silver oxidizing. 17. Label the anode and cathode with charges on the diagram.18. Explain the direction of e- flow through the wire.19. Is this reaction spontaneous? _____ How can you tell? 0016. Only one element is being used in the diagram to the left. The silver plate ionizes and the ions attach to the spoon. Show a half reaction for silver oxidizing. 17. Label the anode and cathode with charges on the diagram.18. Explain the direction of e- flow through the wire.19. Is this reaction spontaneous? _____ How can you tell? 209550614426000270510018732620. Write the half reaction for the anode in the diagram to the left: 21. Write the half reaction for the cathode,22. How many e- are transferred per mole? 23. What is the charge of the Zn electrode? 24. Why is a power source needed in this cell? 0020. Write the half reaction for the anode in the diagram to the left: 21. Write the half reaction for the cathode,22. How many e- are transferred per mole? 23. What is the charge of the Zn electrode? 24. Why is a power source needed in this cell? 17145024193625. Show a half reaction for silver reducing.26. Label the anode and cathode on the diagram to the right.27. What will happen to the mass of the key?28. What will happen to the mass of the silver metal?29. Show the direction of e- flow through the wire on the diagram to the right.30. State the difference between voltaic and electrolytic cells in terms of electrical and chemical energy. 0025. Show a half reaction for silver reducing.26. Label the anode and cathode on the diagram to the right.27. What will happen to the mass of the key?28. What will happen to the mass of the silver metal?29. Show the direction of e- flow through the wire on the diagram to the right.30. State the difference between voltaic and electrolytic cells in terms of electrical and chemical energy. 278130025146031. Why will the mass of the key increase?32. Label the anode, cathode, and the direction of e-flow through the wire.33. State the difference between voltaic and electrolytic cells in terms of spontaneity.34. State the difference between voltaic and electrolytic cells in terms of energy being released or absorbed.0031. Why will the mass of the key increase?32. Label the anode, cathode, and the direction of e-flow through the wire.33. State the difference between voltaic and electrolytic cells in terms of spontaneity.34. State the difference between voltaic and electrolytic cells in terms of energy being released or absorbed.leftbottomElectrochemical Cells Regents Questions1. In a voltaic cell, chemical energy is converted toelectrical energy, spontaneouslyelectrical energy, nonspontaneouslynuclear energy, spontaneouslynuclear energy, nonspontaneously2. A voltaic cell spontaneously convertselectrical energy to chemical energychemical energy to electrical energyelectrical energy to nuclear energynuclear energy to electrical energy3. A voltaic cell differs from an electrolytic cell in that in a voltaic cellenergy is produced when the reaction occursenergy is required for the reaction to occurboth oxidation and reduction occurneither oxidation nor reduction occurs4. Which half-reaction can occur at the anode in a voltaic cell?Ni2+ + 2e- → NiSn + 2e- → Sn2+Zn → Zn2+ + 2e-Fe3+ → Fe2+ + e-5. Which process requires an external power source?neutralization(3) fermentationsynthesis(4) electrolysis6. Which energy transformation occurs when an electrolytic cell is in operation?chemical energy → electrical energyelectrical energy → chemical energylight energy → heat energylight energy → chemical energy7. What is the purpose of the salt bridge in a voltaic cell?It blocks the flow of electrons.It blocks the flow of positive and negative ions.It is a path for the flow of electrons.It is a path for the flow of positive and negative ions.8. Which statement is true for any electrochemical cell?Oxidation occurs at the anode, only.Reduction occurs at the anode, only.Oxidation occurs at both the anode and the cathode.Reduction occurs at both the anode and the cathode.9. Given the balanced equation representing a reaction occurring in an electrolytic cell:2NaCl(l) 2Na(l)?+ Cl2(g)Where is Na(l) produced in the cell?(1) at the anode, where oxidation occurs(2) at the anode, where reduction occurs(3) at the cathode, where oxidation occurs(4) at the cathode, where reduction occursElectrolytic Cells Short AnswerUse the diagram of a key being plated with copper to answer questions 12 through 15.1866900920751. What is the name of the process shown in the diagram? 2. What is the purpose of the battery in this electrolytic cell? 3. Which electrode, A or B, attracts positive copper ions? 4. Given the reduction reaction for this cell: Cu2+(aq) + 2e– → Cu(s) This reduction occurs atA, which is the anode(3) B, which is the anodeA, which is the cathode(4) B, which is the cathode001. What is the name of the process shown in the diagram? 2. What is the purpose of the battery in this electrolytic cell? 3. Which electrode, A or B, attracts positive copper ions? 4. Given the reduction reaction for this cell: Cu2+(aq) + 2e– → Cu(s) This reduction occurs atA, which is the anode(3) B, which is the anodeA, which is the cathode(4) B, which is the cathode1247140379730005. Aluminum is one of the most abundant metals in Earth’s crust. The aluminum compound found in bauxite ore is Al2O3. Over one hundred years ago, it was difficult and expensive to isolate aluminum from bauxite ore. In 1886, a brother and sister team, Charles and Julia Hall, found that molten (melted) cryolite, Na3AlF6, would dissolve bauxite ore. Electrolysis of the resulting mixture caused the aluminum ions in the Al2O3 to be reduced to molten aluminum metal. This less expensive process is known as the Hall process.Write the oxidation state for each of the elements in cryolite. Na: +1 Al: +3 F: –1Write the balanced half-reaction equation for the reduction of Al3+ to Al.Al3+ + 3e– AlExplain, in terms of ions, why molten cryolite conducts electricity. There are freely moving ions in the molten cExplain, in terms of electrical energy, how the operation of a voltaic cell differs from the operation of an electrolytic cell used in the Hall process. Include both the voltaic cell and the electrolytic cell in your answer.lectrolysis uses electrical energy. Voltaic cells produce electrical energy98953236308006. Base your answers to the following questions on the diagram and balanced equation below, which represent the electrolysis of molten NaCl.When the switch is closed, which electrode will attract the sodium ions? cathode, one on the rightWhat is the purpose of the battery in this electrolytic cell? energy sourceWrite the balanced half-reaction for the reduction that occurs in this electrolytic cell. a+ + e– : requires energy, nonspontaneous, 1 cell, electrical energy chemical energy8. The apparatus shown in the diagram consists of two inert platinum electrodes immersed in water. A small amount of an electrolyte, H2SO4, must be added to the water for the reaction to take place. The electrodes are connected to a source that supplies electricity.0000What type of electrochemical cell is shown? electrolytic or electrolysisWhat particles are provided by the electrolyte that allow an electric current to flow? Ions, charged particles, H3O+, or SO42–9. The diagram below shows a system in which water is being decomposed into oxygen gas and hydrogen gas. Litmus is used as an indicator in the water. The litmus turns red in test tube 1 and blue in test tube 2.The oxidation and reduction occurring in the test tubes are represented by the balanced equations below.30289501136650006921500(a) Identify the information in the diagram that indicates this system is an electrolytic cell. A battery is part of the cell and is providing energy that causes the reaction.Electricity is used to operate the cell.(b) Determine the change in oxidation number of oxygen during the reaction in test tube 1. -2 to 0Explain, in terms of the products formed in test tube 2, why litmus turns blue in test tube 2.Litmus turns blue when hydroxide ions are produce0138430010. Which reaction occurs spontaneously?(1) Cl2(g)?+ 2NaBr(aq) Br2(l)?+ 2NaCl(aq)(2) Cl2(g)?+ 2NaF(aq) F2(g)?+ 2NaCl(aq)(3) I2(s)?+ 2NaBr(aq) Br2(l)?+ 2NaI(aq)(4) I2(s)?+ 2NaF(aq) F2(g)?+ 2NaI(aq)11. Which metal reacts spontaneously with a solution containing zinc ions?(1) magnesium????????? (3) copper(2) nickel??????????(4) silver12. Which metal with react with Zn2+ spontaneously, but will not react with Mg2+?(1) Al(3) Ni(2) Cu(4) Ba13. Which of the following metals has the least tendency to undergo oxidation?(1) Ag(3) Zn(2) Pb(4) LiOur Model so far… Complete the table below using your knowledge of voltaic and electrolytic cells.Diagram:Mathematical:Graphical:Narrative: ................
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