Redox Flashcards
what 3 things can you add to ionic half equations ?
H+ / e- / H2O
what is the colour change w/ MnO4- titration ?
purple to colourless
what is the colour change w/ dichromate titration ?
orange to green
outline the process of a redox titration
- measure quantity of unknown conc sol. using pipette into conical flask
- add dilute acid
- gradually add known conc sol. using burette
- stop when mixture changes colour and record vol of oxidising agent used
- repeat and calculate mean titre
what is Iodine-thiosulfate titration used for ?
finding concentration of an oxidising agent
outline the process of finding oxidising agent conc Iodine-thiosulfate titration
- add set vol of [O] agent to excess of KI to form Iodine
- Iodine-thiosulfate titration
- calculate no. of moles of iodine in solution
- calculate conc of [O] w/ first equation
outline the process of Iodine-thiosulfate titration
- add sodium thiosulfate to iodine using burette
- when Iodine solution fades to pale yellow, add starch solution, turning solution blue
- continue to add sodium thio. slowly until decolourises
what is the salt bridge ?
filter paper soaked in potassium nitrate, which allows ions to flow through and balance charges
what electrode is used when no solid metal for electrochemical cell ?
platinum
inert and conducts electricity
in an electrochemical cell, electrons flow ..
from most reactive metal to least
more negative electrode potential means ..?
more easily oxidised - loses electrons
electrode potential of cell =
electrode potential of positive - electrode potential of negative
define standard electrode potential
voltage measured when the half-cell is connected to a standard hydrogen electrode, under standard conditions
a more reactive metal will have a … electrode potential
more negative
a more reactive NON metal will have a … electrode potential
more positive
what equation is at the anode of a fuel cell ?
H2 –> 2H+ + 2e-
what equation is at the cathode of a fuel cell ?
1/2 O2 + 2H+ +2e- –> H2O
what goes in / out at the anode of fuel cell ?
fuel (H2) in / unused fuel out
what goes in / out at the cathode of fuel cell ?
oxidant (O2) in / water out
which direction do electrons flow in fuel cell ?
2 electrons from anode to cathode
state the advantages of electrochemical cells
- more efficient than conventional combustion engines
- produce less pollution
state the disadvantages of electrochemical cells
- toxic chemicals in cell must be disposed of at end of cell life
- chemicals used to make cells are often very flammable
state one difference between fuel cell and modern storage cell
fuel like oxygen required to give electrical voltage
state an advantage of using ethanol over hydrogen as a fuel
is a liquid (less volatile) so easier to store
state an advantage of using hydrogen over conventional fuels
water is only product (no carbon dioxide)
state ways hydrogen can be stored as a fuel
- liquid under pressure
- within solid material
suggest two reasons for feasible electrode potential reactions not taking place ?
- Ea very high
- conditions not standard