final exam Flashcards
(50 cards)
What is the difference between a primary and secondary battery?
Primary batteries cannot be recharged due to slow kinetics
What are the advantages of lithium ion batteries?
lithium has an extremely negative reduction potential >-3
lithium is the lightest and smallest metal
can provide two times the voltage of other batteries
no memory effects - 100% rechargable
What is the issue with large scale liion batteries?
repeated charging can cause the lithium anode to develop dendrites
- largely fixed now with better designs
What occurs in a liion battery?
Anode - LiC6 –> 6C + Li^+ + e^-
Cathode - LiCoO2 + xLi + xe^- –> LiCoO2
lithium ions slide between graphite sheets at anode
Co(IV) is reduced to Co(III) in the form of LiCoO2 at the cathode
Li is kept with carbon to prevent dendrites and short circuiting
slightly less capacity but more effieicent and less risk with graphite anode
What is disproportionation and comproportionation?
Disproportionation - when an element is oxidized and reduced at the same time
Comproportionation - two species of the same element come together to make an intermediate oxidation state
(from a graph… if the lowest (most stable) state is the middle - the species comproportionate if the lower states are on either side - the species disproportinate
How do we determine if a metal oxide can be reduced to pure metal?
using Ellingham diagrams - if any C,CO,CO2 reaction has a more negative delta G than the metal oxide then the compound will be reduced to pure metal under specific temperature
How do we reduce silicon?
silicon is re oxidized to SiCl4, purified by distillation and then re reduced by H2 - produces pure large crystals at 1700 c
Explain the Hall-Heroult process
process used to produce aluminum metal
Mix Al2O3 with a cryolite to lower the melting temperature - Heat to 935C to split Al2O3 into 2Al3+ and 3O2- wich are deionized at the cathode and anode respectively
- aluminum is more dense than cryolite and can be siphoned out
Explain the Bayer process
Way to create Al2O3 for the Hall-Heroult process
- bauxite and NaOH under high pressure - distilled with water and then filtered to produce Al2O3 and H2O from AlO(OH) and H2O
Explain the Downs process
used to produce Na and Cl2 from NaCl
Cathode - Na+ + e- –> Na
Anode - 2Cl- –> Cl2 +2e-
very energy intensive process
- similar processed used on other alkaline earth metals
Explain the Nelson process
electrolysis of NaCl
- Anode - 2Cl- –> Cl2 + 2e-
Cathode - 2H2O + 2e- –> 2OH- + H2
major source of NaOH and Cl2
Industrial considerations and applications of fluorine
Since F is most electronegative, it will react with almost anything - F2 extremely strong oxidizing agent
Extracted from fluorite CaF2 - used to produce HF or F2
CaF2 + H2SO4 –> 2HF + CaSO4
Anode - 2F- –> F2 + 2e-
Cathode - 2H+ + 2e- –> H2
uses molten KF as solvent
Explain the Haber - Bosch process *** likely key
N2 + 3H2 <—> 2NH3 at high temp and pressure
exothermic reaction
high pressure needed to overcome small eq constant
needs Iron catalyst
Have to overcome the super strong N2 bond - interacting with a catalyst effectively lowers the bond order
Define Bronsted and Lewis Acid/base
BA - proton donor
BB - proton acceptor
LA - electron acceptor
LB - electron donor
How do we determine pKa, what does this mean?
-log Ka = pKa
higher Ka or lower pKa = stronger acid
if pka is less than 0 the acid can be considered a strong acid
What is an aqua acid?
Bronsted acids with an OH group - basically an interaction between water and metal cations
- donate a proton to water
strength increases with higher charge of metal ion and decreasing ionic radius
What is the electrostatic parameter?
smaller ions with higher charges are the strongest acids - but like actually not? generally larger atoms deep in the periodic table with high oxidation numbers are acidic
What is a hydroxyacid?
species in which the acidic proton is on a hydroxyl group attached to the central metal core
cannot have a M-O double bond
Ex) Te(OH)6 reacts with water to give TeO(OH)5-
What is an oxyacid?
species in which the acidic proton is on a hydroxyl group attached to the central metal core in which there is also a MO double bond
like H2SO4 which can be written like SO2(OH)2
common when central element has high oxidation stat
What is a general trend for acidity and oxyacids
acidity increases with increasing oxidation number
- the more MO double bonds the more acidic as well
What is paulings rule for oxoacids?
strength increases with number of O double bonded to center
pKa = 8-5p
What two species violate paulings rules
H2CO3 and H2SO3 which have higher and lower pKas than expected respectively
- because they form a complex equilibria in an aqueous soln
Difference between basic and acidic metal oxides?
basic - react with water to from hydroxides (BaO + H2O = Ba(OH)2
acidic - forms hydroxy/oxyacids
(CO2 + H2O = H2CO3
What is it called when a species can act as an acid or a base?
amphoterism
common to group 13 and 14
generally amphoteric in the 4+ oxidation state
