Lecture 274/8/05

Quiz 10 1) A potential of V is calculated (under standard conditions) for a voltaic cell using the following half reactions. What is the E° of the cathode? Anode: Ag(s)  Ag + (aq) + e - Cathode: Ag 2 SO 4 (s) + 2e -  2Ag(s) + SO 4 2- (aq) 2) Which is more easily reduced: Cl 2 or Br 2 ?

Primary Batteries (non-rechargeable) Dry Cell or Zinc-carbon Invented by Georges Leclanche in 1866 E° = 1.5 V Anode:Zn(s)  Zn 2+ (aq) + 2e - Cathode2NH 4 + (aq) + 2e -  2NH 3 (g) + H 2 (g) To keep gas from building up:  Zn 2+ (aq) + 2NH 3 (g) + 2Cl - (aq)  Zn(NH 3 ) 2 Cl 2 (s)  2MnO 2 (s) + H 2 (g)  Mn 2 O 3 (s) + H 2 O (l) Short shelf life zinc since the reaction slowly continues even if battery not being used

Primary Batteries (non-rechargeable) Alkaline battery E° = 1.54 V AnodeZn(s) + 2OH -  ZnO (aq) + H 2 O + 2e - CathodeMnO 2 (aq) + H 2 O + e -  MnO(OH) (s) + OH - Longer shelf life No gas formation Higher concentrations so last longer than dry cell

Primary Batteries (non-rechargeable) Mercury battery E° = 1.35 V Anode:Zn(s) + 2OH -  ZnO (aq) + H 2 O + 2e - Cathode:HgO (aq) + H 2 O + 2e -  Hg (l) + 2OH - Mercury is toxic so must be carefully disposed of Calculators, watches, etc

Primary Batteries (non-rechargeable) Oxyride battery E° = 1.7 V Cathode: NiOOH + H 2 O + e-  Ni(OH) 2 + OH - (1) Anode:MnO 2 (aq) + H 2 O + e -  MnO(OH) (s) + OH - New battery Vacuum pouring technology Should last 2X longer than alkaline battery

Secondary Batteries (rechargeable) Lead battery E° = 2 V Cathode: PbO 2 + 4H + + SO e-  PbSO 4 + 2H 2 O (1) Anode:MnO 2 (aq) + H 2 O + e -  MnO(OH) (s) + OH - Put 6 in series to get 12 V