lol Flashcards
Cell
A redox system which contains chemicals that react together to create electrical energy
Structure
Two metals in contact with an electrolyte
Size of PD depends on
Type of electrode
Concentration of electrolyte
Battery
2 or more cells connected in series
Non rechargeable batteries
Reaction at electrodes is irreversible
When all reactants run out, no voltage produced
Rechargeable batteries
Reaction at electrodes is reversible
Connect battery to pins and reverse current through it
Fuel cell
A cell which generates an electrical current as long as fuel and O2 are supplied
Negative electrode
H2 converted to H+ oxidation
H2 (g) -> 2H+ + 2e-
H+ travels through electrolyte
e- travels into electrical circuit generating a current
Positive electrode
H+ reacts w oxygen to form water reduction
4H+ (aq) + 4e- + O2 -> 2H2O
Overall reaction fuel cell
2 H2 (g) + O2 (g) -> 2 H2O (g)
Advantages of fuel cells
More accessible materials
Lower emissions
No toxic fumes
Fuel added makes it last longer
Disadvantages of fuel cells
Less accessible fuels
Less available infrastructure
H2 is explosive
Corrosion
The gradual destruction of materials by reaction with substances in the environment
Rust
The corrosion of iron
Forms hydrated iron oxides and hydroxide
Hydroxide ions half equation
4e- + O2 + 2H2O -> 4OH-
Iron ions half equation
Fe -> Fe 2+ + 2 e-
Iron further oxidised
Fe 2+ + O2 -> Fe 3+ + 2O2-
Iron hydroxides break down into oxides releasing water
Fe (OH) 2 -> FeO + H2O
Barrier method of preventing corrosion
Coating with paint or plastic
Oiling or greasing
Electroplating with less reactive metal
O2 and H2O cannot get to surface
Sacrificial protection
Blocks of more reactive metal corrode in place of less reactive metal
Galvanising adds a coat of zinc to stop O2 and H2O reaching surface
If scratched, Zn corrodes and not Fe
Low carbon steel
Easily shaped
Car bodies
0.1 to 0.3
High carbon steel
Strong but brittle
Construction
0.25 to 0.5
Stainless
Resists corrosion
Cutlery
Cu/Ni
Higher carbon content means
Harder for layers to slide, so higher CC = less malleable = less easy to slide = more brittle
Why is Chromium used in steel (iron alloys)
More reactive, adding sacrificial protection, reducing corrosion
Aluminum - why unpainted?
Forms a layer of unreactive AlO on surface, 2-3nm thick that doesn’t flake away
What are alloys of Al used for
Low density
Cu + Tin
Bronze
Cu + Zinc
Brass
Nitinol
Memory alloy reforms og shape when heated and cooled
24 karats
100% gold
12 karats
50% gold
Why is gold alloyed
Hardness
Colour
Cheap
Composites
Reinforcement
Matrix
Reinforcement provides strength
Matrix surrounds and holds reinforcement in place
Ceramics
Shaping wet clay and heating in furnace
Forms cross links in a giant covalent structure
Soda-lime glass
Sand limestone sodium carbonate
Borosilicate
Sand and boron trioxide
Higher melting point
Glass structure
Giant covalent
Melting point in polymers
Strength of IM forces holding polymer chains together
Longer chain = stronger forces
Monomer used also affects strength of IM forces
Polyethene reaction conditions
HDPE
LDPE
Thermosoftening polymer
Melts
No cross links
Haber process
Methane = Natural gas
Methane + steam -> Hydrogen + Carbon monoxide
Hydrogen + oxygen = water [removes o2 from air to leave N]
Nitrogen + Hydrogen -> Ammonia
N2 (g) + 3H2 (g) -> 2NH3 (g)
Conditions for haber
450 degrees
200 atmospheres
Iron catalyst
What does condensing ammonia do
Unused reactant gases separated from ammonia easily and recycled into reactor
Equilibrium position shifts to right as product is removed
NPK fertiliser
Formulation and contains carefully measured salt quantities
Nitrogen
Amino caids/proteins
Phosphorous
DNA, root growth, flower production
Potassium
Growth and crop yield
Why is manure not used
Parasites
Where does nitrogen come from in NPK
Haber
Where does ammonium nitrate come from
Nitric acid + Ammonia -> Ammonium nitrate
HNO3 + NH3 -> NH4NO3
Potassium salts
Mined
Phosphorous
Extracted from phosphate rock
Phosphate rock and H2SO4
Monocalcium phosphate
Calcium sulfate
Phosphate rock and HNO3
Phosphoric acid
Calcium nitrate
Phosphate rock and H3O4P
Calcium phosphate
HDPE
High density
Higher melting point
LDPE
Low density
Lower melting point
