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CHEM 231 > final exam > Flashcards

final exam Flashcards

1
Q

What is the difference between a primary and secondary battery?

A

Primary batteries cannot be recharged due to slow kinetics

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2
Q

What are the advantages of lithium ion batteries?

A

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

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3
Q

What is the issue with large scale liion batteries?

A

repeated charging can cause the lithium anode to develop dendrites
- largely fixed now with better designs

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4
Q

What occurs in a liion battery?

A

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

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5
Q

What is disproportionation and comproportionation?

A

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

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6
Q

How do we determine if a metal oxide can be reduced to pure metal?

A

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

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7
Q

How do we reduce silicon?

A

silicon is re oxidized to SiCl4, purified by distillation and then re reduced by H2 - produces pure large crystals at 1700 c

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8
Q

Explain the Hall-Heroult process

A

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

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9
Q

Explain the Bayer process

A

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

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10
Q

Explain the Downs process

A

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

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11
Q

Explain the Nelson process

A

electrolysis of NaCl
- Anode - 2Cl- –> Cl2 + 2e-
Cathode - 2H2O + 2e- –> 2OH- + H2
major source of NaOH and Cl2

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12
Q

Industrial considerations and applications of fluorine

A

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

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13
Q

Explain the Haber - Bosch process *** likely key

A

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

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14
Q

Define Bronsted and Lewis Acid/base

A

BA - proton donor
BB - proton acceptor

LA - electron acceptor
LB - electron donor

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15
Q

How do we determine pKa, what does this mean?

A

-log Ka = pKa
higher Ka or lower pKa = stronger acid
if pka is less than 0 the acid can be considered a strong acid

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16
Q

What is an aqua acid?

A

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

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16
Q

What is the electrostatic parameter?

A

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

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17
Q

What is a hydroxyacid?

A

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-

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18
Q

What is an oxyacid?

A

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

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18
Q

What is a general trend for acidity and oxyacids

A

acidity increases with increasing oxidation number
- the more MO double bonds the more acidic as well

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19
Q

What is paulings rule for oxoacids?

A

strength increases with number of O double bonded to center
pKa = 8-5p

20
Q

What two species violate paulings rules

A

H2CO3 and H2SO3 which have higher and lower pKas than expected respectively
- because they form a complex equilibria in an aqueous soln

21
Q

Difference between basic and acidic metal oxides?

A

basic - react with water to from hydroxides (BaO + H2O = Ba(OH)2

acidic - forms hydroxy/oxyacids
(CO2 + H2O = H2CO3

22
Q

What is it called when a species can act as an acid or a base?

A

amphoterism
common to group 13 and 14
generally amphoteric in the 4+ oxidation state

23
Q

Explain silica condensation to form glass

A

take from corrected assignment 4

24
Q

What is a zeolite?

A

zeolites can absorb and release large amounts of water or ions
- molecular sieves
important in commercial applications
- crystalline aluminosilicate material
MxAlO2xSiO2y.mH2O
tend to have a Si/Al ratio of 0.5

made of primary building blocks of silica and alumina tetrahedra - 4/6 ring

secondary structure called a sodalite unite - 24 tetrahedra
connection of secondary units produces pores and internal cavities in the structure

25
Q

How are zeolites used as solid acid catalysts?

A

used for cracking petroleum
- ion exchange
ZSM5 - has strongly acidic sites - great for breaking down carbons

26
Q

What are the three kinds of selectivity that makes zeolites useful

A

Reactant selectivity - only reactants that can enter the pores can reach the catalytic sites

Product selectivity - only products that can leave the zeolite will be formed

Transition state selectivity - only reactions with transition states that will fit in the cavity are possible

27
Q

Define hard and soft acid / bases

A

Hard acids - not polarizable and usually charged - small cations
Soft acids - polarizable - deeper in the periodic table
Hard bases - small negatively charged
Soft bases - larger but still negatively charged

28
Q

What is important about the hard/soft acid/base classification

A

hard acids form stronger acid base bonds with hard bases, soft acids form stronger bonds with soft bases

hard acid/base are electrostatic in nature
soft are covalent (size differences

29
Q

What is a superacid?

A

an acid that is stronger than H2SO4
typically a mixture of a strong lewis acid and a strong bronsted acid
will protonate hydrocarbons

30
Q

What is a superbase?

A

a nicki minaj song
- bases which are more efficient proton acceptors than OH-

31
Q

Why is BF3 weaker than BCl3

A

BF3 has minor resonance contribution from pi bonding of F 2p orbitals and empty 2p boron orbital - no pi contribution with BCl

32
Q

Why is CO2 a gas while SiO2 is solid?

A

2p elements will form pi bonds while other p block elements cannot do this

33
Q

Why is there no graphite analog of Si?

A

2p elements will form pi bonds while other p block elements cannot do this

34
Q

Why is N2 a gas while P4 is a solid?

A

2p elements will form pi bonds while other p block elements cannot do this

35
Q

Why is O2 a gas while sulfur is solid?

A

2p elements will form pi bonds while other p block elements cannot do this

36
Q

What are the phosphorus allotropes?

A

White, black red and violet
white is used in smoke grenades

37
Q

Why is graphite different from diamond?

A

Graphite is more thermodynamically stable than diamond but is kinetically hidered - the state is metastable

38
Q

Why does group 14 have so many different properties?

A

Non metals, metalloids and metals are all in this group - has to do with size effects ionization energy and structureSol

39
Q

Solid oxides of group 14 are often found as

A

MO not MO2 - the inert pair effect

40
Q

How do we recover nitrogen?

A

distillation of liquid air on a large scale - separation by boiling point
- separation by membranes ona small scale
- used as an inert gas in metal production
- used as a refrigerant
- used in ammonia production

41
Q

What is an example of comproportionation used in purification?

A

Claus process for sulfur production - H2S and SO2 comproportionate to S

42
Q

What does the catalyst do in the Haber Bosch process - explain with an MO diagram?

A

Basically lowers the bond order of N2 from 3 to 2 - Electrons from catalyst join anti bonding orbitals with N2 meaning there is a +2 e- going into the final orbital

43
Q

What is an example of disproportionation used in synthesis?

A

Ostwald process - NO2 disproportionates into HNO3 and NO

44
Q

What is a charge transfer bond and where do we see them?

A

When lewis acids and bases come together to fomr a complex called an adduct - charge transfer bond is formed from the base sharing electron density with the acid - is the component behind superacids

45
Q

ACTUAL example of a comproportionation reaction

A

Claus process - sulfer production
- 4H2S + 2SO2 —> 6S + 4H2O
comproportionate to intermediate oxidation state

46
Q

ACTUAL example of disproportionation reaction?

A

High Z group 14 elements found as MO
SnO —> Sn + SnO2

47
Q

Periodic trends for atomic radii, eneg, Zeff, ionization energy

A

atomic radii - decrease left to right, increase down
eneg - increase left to right, decrease down
Zeff - increase left to right
ionization energy - increase left to right, decrease going down

48
Q

Where is water formed in each of the main fuel cells? (alkaline, PEM, solid oxide, methanol)

A

Alkaline - anode
PEM - cathode
Solid Oxide - anode
M/ethanol - cathode

CHEM 231 (3 decks)

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