Exploring Electrochemistry: Batteries, Voltaic Cells, and Transition Metals
Dive into the realm of electrochemistry with a focus on batteries, voltaic cells, and transition metals. Discover the principles behind lead acid batteries, fuel cells, and electrolytic cells, along with practical applications in powering medical devices and industrial use. Unravel the mysteries of electrochemical processes and their relevance in modern technology and everyday life.
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Presentation Transcript
Announcements I Mastering Assignment due this Saturday Lab Next Week Quiz on Experiments 9 and 10 and Electrochemistry and Start to Transition Metals Experiment 9 lab report due Mon./Tues.
Announcements II Today s Lecture Electrochemistry Batteries applied voltaic cells Electrolytic Cells Transition Elements (Ch. 24) Absorption of visible light Electron configuration and characteristics of transition metals
Chapter 18 Electrochemistry Batteries - Questions 1. If 100 g. of Pb(s) is used in a lead acid battery, what mass of PbO2(s) is required for best efficiency? 2. How many Amp Hours will this provide in a 12 V battery? 3. Will the voltage generated by a lead acid battery be affected by how depleted it is? 4. What is the voltage when it is 90% depleted (vs. initial voltage)? On this
Chapter 18 Electrochemistry Other Voltaic Cells Examples: Fuel Cells Voltaic cell where reactants (fuel plus oxygen) flow to electrodes to produce electricity New Toyota Fuel Cell vehicle available (reported last year in Sacramento Bee) Reactions: 2H2(g) + 4OH-(aq) And O2(g) + 2H2O(l) + 4e- If H2 is produced from electrolysis using solar energy, 100% renewable More commonly, H2 is made from natural gas 4H2O(l) + 4e- 4OH-(aq)
Chapter 18 Electrochemistry Other Voltaic Cells Examples: Powering Medical Devices Batteries have a limited lifetime, so pacemakers and defibrillators must be surgically removed to replace batteries Another 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
Chapter 18 Electrochemistry Electrolytic Cells Example Reactions 1. Electrolysis of water (opposite of fuel cell example) Anode: H2O oxygen is oxidized to O2(g) Cathode: H2O hydrogen is reduced to H2(g) 2. Industrial Use Electroplating (Chrome, nickel, silver plating possible) using external potential to deposit metal to electrode
Chapter 18 Electrochemistry Electrolytic Cells Example Reactions 3. Electrolysis of Mixtures e.g. analysis External potential will work on easiest to oxidize/reduce pair For example, if we have a mixture of NaI and NaCl in water, electrolysis will cause the following reactions: Na+(aq) + e- Na(s) E = -2.71 V H2O(l) + 2e- H2(g) + 2OH-(aq) E = -0.83 V 2Cl-(aq) Cl2(g) + 2e- E = +1.36 V 2I-(aq) I2(aq) + 2e- E = +0.54 V 2H2O(l) O2(g) + 4H+(aq) + 4e- E = 1.23 V
Chapter 18 Electrochemistry Electrolytic Cells - Questions 1. Which of the following changes in switching from a voltaic to an electrolytic cell? a) Charge on anode/cathode b) Which electrode (e.g. anode) does oxidation/reduction c) Ion migration to electrode 2. An anode in an electrolytic cell is used to measure oxalate (E = -0.49V) in the presence of pyruvate (E = -0.70V). Which will oxidize first in a mixture?
Chapter 18 Electrochemistry Electrolytic Cells Questions Cont. 3. When a battery is being recharged, which of the following happens? a) Electrode charge changes b) Electrode reaction changes (anode oxidation becomes cathode) Used as voltaic cell battery powers light bulb External Power Generator to charge battery + - + - Pb(IV) Pb(II) Pb(II) Pb(IV) Reactions reverse (products to reactants to replenish charge)
Chapter 18 Electrochemistry Electrolytic Cells Questions cont. 4. 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 = dL + d2/2 and AW(Cr) = 52.00 g/mol and (Cr) = 7.19 g/cm3
Chapter 24 Transition Metals Overview Compared with the main group elements, differences in transition metals are smaller Variation is in how full d-shell orbitals are Much 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
Chapter 24 Transition Metals Color A variety of compounds are colored because they absorb visible light Most organic compounds have strong bonds and a large energy gap between ground and excited states Transition metals, in coordination complexes, tend to have weaker bonds and smaller energy gaps, so that they often absorb visible light
Chapter 24 Transition Metals Color Cobalt Chloride Compounds In 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 pink This is the basis for indicator Drierite (show samples)
Chapter 24 Transition Metals Properties D-Block Elements (show on periodic table) Electron Configuration nS 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 shell Filling 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
Chapter 24 Transition Metals Properties cont. Filling exceptions 1st row Cr (4s13d5 instead of 4s23d4) and Cu (4s13d10 instead of 4s23d9) due to extra stability of half- and completely-filled d orbitals Electron Configuration for ions electron removal in oxidation is different: first lost are ns electrons and then (n-1)d electrons reason is because outside a cation, (n-1) d electrons are more strongly attracted to the nucleus than the ns electrons
Chapter 24 Transition Metals Properties cont. Size decreases slightly across a row so 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
Chapter 24 Transition Metals Properties cont. Oxidation State All 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)
Chapter 24 Transition Metals Questions 1. Give 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. 3. Why are only the elements Cu and Ag able to form stable +1 oxidation states? 4. What is the maximum oxidation state expected for V?
