redox and electrode potentials Flashcards
(19 cards)
describe how to set up 2 half cells of Cu and Zn
(negative side): solution containing 1moldm-3 of Zn2+ (aq) with a zinc electrode
wire connecting from zinc electrode to voltmeter then to copper electrode which is half in a solution of 1 moldm-3 Cu2+ (aq)
have a connecting salt bridge in both solutions
describe what happens in an electrochemical cell
electrodes connected by a wire (allows electrons to flow)
solutions are connected with a salt bridge (allows ions to flow)
electrons will flow from the more reactive metal to the less reactive metal
what happens at the negative electrode
negative electrode becomes oxidised (acts as an reducing agent), electrons will flow from this electrode through the wire to positive electrode
what happens at the positive electrode
will gain electrodes, therefore becomes reduced
metal (s) forms and deposits on the electrode if metal
how do you compare the electrode potential of different half-cells
each cell compared to a standard hydrogen half-cell under standard conditions (100kPa, 298K, concentration of 1moldm-3)
what is E⌀, what does a negative value show
standard electrode potential, the more negative the value the better then half cells acts as a reducing agent, will become oxidised more easily
describe how to set up a standard hydrogen half cell
solution containing 1 moldm-3 H+ (aq)
platinum electrode
glass tube with holes in to allow bubbles to escape
H2 (g) at 298k, 100kPa into glass tube
how do rechargeable batteries work
made from nickel/cadmium cells, can be recharged by reversing the direction of the reactions via large external current to move electrons back in reverse direction
how do lithium batteries work (phone battery)
positive electrode made from lithium cobalt and negative electrode made from carbon, electrodes are arranged in layers with a solid polymer electrolyte in between them
how do fuel cells (alkaline hydrogen-oxygen) work, benefits and disadvantages
2 electrodes separated by partially permeable membrane, energy from reaction of hydrogen fuel cell and oxygen used to create a voltage
eco-friendly alternative as only product is water
H2 used can be from crude oil or from electrolysis of water (uses large quantities of electricity)
how are rechargeable batteries in cars engine made
from lead plates dipped into solution of sulfuric acid
within the battery there are number of connected cells, each cell made up from 2 plates
negative plate is lead and positive plate is lead coated with lead(IV) oxide
how do you calculate emf of 2 ions (eg Fe3+,Fe2+)
platinum electrode is used and placed in a solution of 1moldm-3 of Fe2+ and Fe3+
how do you balance half equations
- write half equation for reduction reaction
- balance electrons
- balance charges
- balance H2 and O2 ions without changing charge
what titration is used to determine concentration of reducing agents
potassium manganate
what titration is used to determine concentration of oxidising agents
sodium thiosulfate
give the overall equation between manganate titration and Fe2+
MnO4- + 8H+ + 5Fe2+—> Mn2+ + 4H2O + 5Fe3+
give the overall equation between manganate titration and ethanedioc acid
2MnO4- + 6H+ + 5(COOH)2 —–> 2Mn2+ + 8H2O + 10CO2
give the overall equation between an iodine-thiosulfate titration
2S2O3²- + I2—> 2I- + S4O6²-
describe how to do the iodine-thiosulfate titration
Na2S2O3 added to burette
solution of oxidising agent and excess potassium iodide added to conical flask
yellow-brown to pale yellow solution, near end point starch is added, turning blue/black if iodine present then disappearing for end point
