Lecture 26 Background Oxidation Numbers bonding Indicates the number of electrons lost gained or shared as a result of chemical Allows us to see when electrons move in a reaction The change in the oxidation state of a species lets you know if it has undergone oxidation or reduction Rules Not all but important ones Make sure to study all of them Free element is 0 Monatomic ion is the same as the charge of the ion Fluorine is always 1 H is usually 1 O is usually 2 Sum of oxidation numbers should equal charge of the compound Know cathode anode characteristics view concept sheet Questions 1 The bacterium Nitrosomonas sp first converts ammonia NH3 to nitrite NO2 a What is the oxidation number of nitrogen in NH3 b What is the oxidation number of nitrogen in NO2 c Balance the half reaction under basic conditions NH3 NO2 2 Find the oxidation numbers for the following a nitrogen in NH b chlorine in Cl O c chromium in Cr O d vanadium in VO and VO e cobalt in Co OH f chromium in Cr OH 3 Identify what is being oxidized what is reduced which is the oxidizing agent and reducing agent Zn s CuSO4 aq ZnSO4 aq Cu s 4 Consider the redox reaction 3Cu2 2Al 2Al3 3Cu How many electrons are transferred in the balanced reaction Lecture 27 STEP FOR REDOX BALANCING you can skip step 1 for the most part 1 Assign oxidation numbers 2 Break into half reactions 3 Balance non O and H elements 4 Add water s to balance oxygen cont next page 5 Add H to balance hydrogens if ACIDIC you DON T do 6a 6b 6 Add electrons to get charges to be the same note every electron adds 1 charge a b The side with both H and OH makes water H2O If BASIC add OH to both sides same amount of H left 7 Multiply to get electrons to cancel 8 Combine and cancel equation 5 Given the following oxidation reduction reaction VO2 aq Cr2O7 2 aq Cr3 aq The reagent being oxidized The reagent being reduced The number of electrons transferred Balance the equation in acid solution 6 Complete and balance the following redox reaction in acidic solution As s H2AsO4 aq AsH3 aq Question VO2 aq Identify Lecture 28 29 Background Know difference between galvanic voltaic and electrolytic cells Gibbs free energy Cell notation Anode Cathode Reactant Product Reactant Product Example Zn s Zn2 1 0M Cu2 1 0M Cu s Anode reaction Zn s Zn2 2e Cathode reaction Cu2 2e Cu s Balanced redox reaction overall Zn s Cu2 Zn2 Cu s Be careful when setting up Q conc can take place too Salt bridge Units of voltage and coulomb Acronym RED CAT AN OX reduction at cathode anode for oxidation Cell Potential Electromotive Force emf difference in the electric potential between two electrodes Positive cell potentials are spontaneous Ecell values are always reported as reduction potentials Measured against a standard hydrogen electrode Ecell E cathode E anode A higher more positive reduction potential is more likely to be a cathode lower would be anode Nernst Equation at equilibrium AT ANY TEMP Eo cell 2 303RT nF log K ONLY AT 298K Eo cell 0 0592 n log K Nernst Equation for non standard conditions AT ANY TEMP E cell Eo cell RT nF ln Q ONLY AT 298K E cell Eo cell 0 0592 n ln Q Faraday s constant 96500 C mol Know how what equations to use for converting for K to G to Eo E E RT nF lnQ VIDEO Explaining Nernst Equation https www youtube com watch v jousNNceCXs Question 7 Consider the voltaic cell with the following components and identify each statement as true or false Ag e Ag 0 80V Zn2 2e Zn 0 76V A B The zinc electrode is the anode Electrons will flow through the circuit from the zinc electrode to the silver electrode C Reduction occurs at the zinc electrode while operating D E The mass of the silver electrode will increase while operating The concentration of Zn2 will decrease as the cell operates 8 Write the following reaction in terms of cell notation 3 Pb aq 2 Al s 3 Pb s 2 Al aq 9 a What is E cell for the reaction Au s 3 Ca aq 2 Au aq 3 Ca s b Using the reduction potentials identify which species is the best oxidizing agent and reducing agent 10 Calculate Eo cell for each of the following balanced redox reactions and determine whether the reaction is spontaneous as written a O2 g 2H2O l 4Ag s 4OH aq 4Ag aq b Br2 l 2I aq 2Br aq I2 s Reduction Potentials Ag e Ag E 0 80 O2 2H2O 4OH E 0 40 Br2 2Br E 1 09 I2 2I E 0 54 11 Consider the following reaction Cu s 2Ag aq Cu2 2Ag s If Ag 1 0M and Cu2 0 020M what is the cell potential at 20 C Ag e Ag E 0 80 Cu2 2e Cu E 0 34 12 What is the equilibrium constant K at 298K for an electrochemical cell when E 0 025 V and n 3 13 Calculate G and E Cell for this redox reaction with an equilibrium constant of K 4 6 10 2 at 298K Mn Zn2 Mn2 Zn 14 Given the following reaction 2 Al s 3 Mn2 aq 2 Al3 aq 3 Mn s The standard cell potential E cell is 0 48 V the concentration of Al3 is 1 0 M What is the E value when concentration of Mn2 is 0 05 M Assume T is 298K 15 A galvanic cell consists of a silver electrode in a 1 0 M Ag solution and a magnesium electrode in a 1 0 M Mg2 A schematic of the cell as well as the standard reduction potentials for Ag and Mg2 are given below a What is the overall balanced reaction that occurs in the cell b What is the flow of electrons element to element in the cell c Which half cell is the anode and which is the cathode d What is the standard cell potential for this reaction Lecture 30 16 True or False for the following a True or False Primary batteries are rechargeable while secondary batteries are b True or False A fuel cell can eventually go dead because it stores a limited c True or False Gold silver and platinum are examples of noble metals that do disposable amount of reactants not corrode d True or False In an electrolytic cell reduction occurs at the anode and oxidation occurs at the cathode Lecture 31 34 17 Write a nuclear equation for the indicated decay of each of the following nuclides A 210 Ra undergoes alpha decay B 103 Pd undergoes electron capture C 15 O undergoes positron emission 18 What nuclide undergoes neutron emission to form 87 Br 19 235 U undergoes fission by one neutron to produce 133 Sb 3 neutrons and what other nuclide 20 A radioactive sample contains …
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