redox topic 3 and 14 Flashcards
what does electron transfer in redox cause
creates flow of electrons so a current
salt bridge
unreactive ions to carry flow of charge usualy KNO3
what are cell potentials measured aganst
standard hydrogen elecrode
what are -ve potentials good for
reducing agents and easily oxidised
what are psoitive potentials good for
easily reduced and good oxididsing agents
what does a positive emf mean
reaction is spontaneous
greater the emf - greater the transfer of electrons
E (cell) =
RHS - LHS
reduction vs oxidation
why are -ve ptentials best reducing agenst
lose e most easily
why is emf positive but no reaction occurs
rate of reaction is so slow you cant see anything happen
for Zn —> Zn2+ + 2e-
what does increasing zn2plus conc do
eqm shifts to the left so reducing the amount of electron loss so zn half cell becomes less negative
for cu2+ +2e- —-> Cu
what ahppens if conc of cu 2+ increases
eqm shifts to the right so increasing association of cu 2 plus and electrons so half cell becomes more positive due to less e in circuit
what do fuel cells do
generate electrical current that doesnt need recharging
what happens with fuel cells
chemicals stored seperatelt outside cell and fed in when electricity is neeeded
for alkaline hydrogen oxygen fuel cells
what goes in and out at -ve electrode
H2 in and H20 out
for alkaline hydrogen oxygen fuel cells
what goes in at positive electrode
oxygen
for alkaline hydrogen oxygen fuel cells
where do e flow
from -ve to +ve electrode
what do oh ions go through
anion exchnage membrane towards -ve electrode
what electrolytel in membrane
KOH
for alkaline hydrogen oxygen fuel cells what are the eqautions
2H2+ 4OH- —-> 4H20 +4e-
O2 + 2H2O +4e- —> 4OH-
overall = 2H2 + O2 —> 2H20
acidic fuel cells
what gas goes in at negative electrode
H2
acidic fuel cells
what gas goes in at positive fuel cell
oxygen
what happens at -ve electrode
platinum cat splits hydrogen into protons and electrons
2H2 —> 4H+ + 4e-
acidic fuel cells where does e move
from negative to posiitve
how do protons get to positive electrode
H+ ions pass through proton exchange membrane
what happens at positive electrode
O2 combines with H+ and e- to make H20
O2 + 4H+ +4e- —-> 2H2O
what do new fuel cells use
alcohol
how do alcoholic fuel cells work
CH3OH +H2O –> CO2 + 6e- + 6H+
6H+ + 6e- + 3/2 O2 —> 3H2O
what does H2SO4 in redox do
provides H+ ions for redox catalyst
iron - manganate titration endpoint
colourless to faint pink
what checks shoud made for iorn manganate titrations
make sure iron is fully dissolved
wash containers so iron isn’t lost
