Chem. 1B – 11/10 Lecture - PowerPoint Presentation

1. Chem. 1B – 11/10 Lecture

2. Announcements IMastering – Assignment due this SaturdayLab Next WeekQuiz on Experiments 9 and 10 and Electrochemistry and Start to Transition MetalsExperiment 9 lab report due Mon./Tues.

3. Announcements IIToday’s LectureElectrochemistryBatteries – applied voltaic cellsElectrolytic CellsTransition Elements (Ch. 24)Absorption of visible lightElectron configuration and characteristics of transition metals

4. Chapter 18 ElectrochemistryBatteries - QuestionsIf 100 g. of Pb(s) is used in a lead acid battery, what mass of PbO2(s) is required for best efficiency?How many Amp–Hours will this provide in a 12 V battery?Will the voltage generated by a lead acid battery be affected by how “depleted” it is?What is the voltage when it is 90% depleted (vs. initial voltage)?On this

5. Chapter 18 ElectrochemistryOther Voltaic CellsExamples:Fuel CellsVoltaic cell where reactants (fuel plus oxygen) flow to electrodes to produce electricityNew Toyota Fuel Cell vehicle available (reported last year in Sacramento Bee)Reactions: 2H2(g) + 4OH-(aq) ↔ 4H2O(l) + 4e-And O2(g) + 2H2O(l) + 4e- ↔ 4OH-(aq)If H2 is produced from electrolysis using solar energy, 100% renewableMore commonly, H2 is made from natural gas

6. Chapter 18 ElectrochemistryOther Voltaic CellsExamples:Powering Medical DevicesBatteries have a limited lifetime, so pacemakers and defibrillators must be surgically removed to replace batteriesAnother option is to run devices off of blood glucose oxidation (C6H12O6(aq) + O2(aq) ↔ C6H10O6(aq) + H2O2(aq) - requires enzyme)Either attachment of enzyme to electrode or electrodes for H2O2 oxidation or reduction can be used to generate electricity

7. Chapter 18 ElectrochemistryElectrolytic CellsExample ReactionsElectrolysis of water (opposite of fuel cell example)Anode: H2O – oxygen is oxidized to O2(g)Cathode: H2O – hydrogen is reduced to H2(g)Industrial Use – Electroplating (Chrome, nickel, silver plating possible) – using external potential to deposit metal to electrode

8. Chapter 18 ElectrochemistryElectrolytic CellsExample ReactionsElectrolysis of Mixtures – e.g. analysisExternal potential will work on easiest to oxidize/reduce pairFor example, if we have a mixture of NaI and NaCl in water, electrolysis will cause the following reactions:Na+(aq) + e- ↔ Na(s) Eº = -2.71 VH2O(l) + 2e- ↔ H2(g) + 2OH-(aq) Eº = -0.83 V2Cl-(aq) ↔ Cl2(g) + 2e- Eº = +1.36 V2I-(aq) ↔ I2(aq) + 2e- Eº = +0.54 V2H2O(l) ↔ O2(g) + 4H+(aq) + 4e- Eº = 1.23 V

9. Chapter 18 ElectrochemistryElectrolytic Cells - QuestionsWhich of the following changes in switching from a voltaic to an electrolytic cell?Charge on anode/cathodeWhich electrode (e.g. anode) does oxidation/reductionIon migration to electrodeAn anode in an electrolytic cell is used to measure oxalate (Eº = -0.49V) in the presence of pyruvate (Eº = -0.70V). Which will oxidize first in a mixture?

10. Chapter 18 ElectrochemistryElectrolytic Cells – Questions – Cont.+-When a battery is being recharged, which of the following happens?Electrode charge changesElectrode reaction changes (anode – oxidation becomes cathode) Used as voltaic cell – battery powers light bulb+-External Power Generator – to charge batteryReactions reverse (products to reactants to replenish charge)Pb(IV) → Pb(II)Pb(II) → Pb(IV)

11. Chapter 18 ElectrochemistryElectrolytic Cells – Questions – cont.A steel rod is being chrome plated from Cr3+. If the rod has a diameter of 10 cm and a length of 150 cm, how long does it take to chrome plate the rod to a thickness of 1 mm, if a current of 20 A is applied during the chrome plating process?V(plating) = (rod surface area)(plating thickness)Rod surface area = pdL + pd2/2 and AW(Cr) = 52.00 g/mol and r(Cr) = 7.19 g/cm3

12. Chapter 24 Transition MetalsOverviewCompared with the main group elements, differences in transition metals are smallerVariation is in how full d-shell orbitals areMuch of the interesting chemistry is from Coordination Compounds (metal – ligand complexes)Focus will be on types of compounds and their relationship to the electron configurations

13. Chapter 24 Transition MetalsColorA variety of compounds are colored because they absorb visible lightMost organic compounds have strong bonds and a large energy gap between ground and excited statesTransition metals, in coordination complexes, tend to have weaker bonds and smaller energy gaps, so that they often absorb visible light

14. Chapter 24 Transition MetalsColor – Cobalt Chloride CompoundsIn Quantitative Analysis Lab, we analyze an aqueous mixture of Co2+ and Cr3+Students tend to think that Co2+ is the blue solution (it is the red/purple solution) Why? Co in inorganic compounds (anhydrous CoCl2, CoO) is blue, but in a coordination complex with water it turns purple and then pinkThis is the basis for indicator Drierite (show samples)

15. Chapter 24 Transition MetalsPropertiesD-Block Elements (show on periodic table)Electron ConfigurationnS and (n-1)d shells are similar in energy (depends on several factors)transition metals start on the 4th row because only 3rd row (n = 3) capable of having d shellFilling goes 4s → 3d → 4p (with a few exceptions) or 5s → 4d → 5p (for 5th row)Filling for 6th row is more complicated: 6s → 4f (lanthanides) → 5d → 6p

16. Chapter 24 Transition MetalsProperties – cont.Filling exceptions – 1st rowCr (4s13d5 instead of 4s23d4) and Cu (4s13d10 instead of 4s23d9) due to extra stability of half- and completely-filled d orbitalsElectron Configuration – for ionselectron removal in oxidation is different: first lost are ns electrons and then (n-1)d electronsreason is because outside a cation, (n-1) d electrons are more strongly attracted to the nucleus than the ns electrons

17. Chapter 24 Transition MetalsProperties – cont.Sizedecreases slightly across a rowso right hand transition metals (e.g. silver) are more dense than left hand metals (titanium)Increase in size from 4th row to 5th row but little change between 5th and 6th row (Lanthanide Contraction) due to filling of 4f orbitals

18. Chapter 24 Transition MetalsProperties – cont.Oxidation StateAll elements but Cu column will lose 2 ns electrons (Cu column is stabilized in +1 state due to full d orbital)Left hand side elements tend to lose additional d orbitals (up to complete emptying)

19. Chapter 24 Transition MetalsQuestionsGive the electron configurations for: V, Fe, Ni, Cu, Fe3+ and Ni2+2. Explain why Fe3+ is a stable ion while Mn3+ is not very stable.Why are only the elements Cu and Ag able to form stable +1 oxidation states?What is the maximum oxidation state expected for V?