Elecrotrodes Flashcards
What is oxidation
Loss of electrons / increase in oxidation number
What is reduction
Gain of electrons/ reduction in oxidation number
Rules for assigning oxidation numbers:
Any element on its own
0
Rules for assigning oxidation numbers:
A simple ion
The charge on the ion
Rules for assigning oxidation numbers: a group 1,2 or 3 element in a compound
Charge is equal to group number, always positive
Rules for assigning oxidation numbers:
Oxygen in a compound
Usually -2
Rules for assigning oxidation numbers:
Group 7 element in a compound
Usually -1
Rules for assigning oxidation numbers:
Hydrogen bonded to non-metal
+1
Rules for assigning oxidation numbers: a compound
The sum of oxidation numbers of all atoms and ions in a compound is zero
Rules for assigning oxidation numbers:
Complex ion
The sun of oxidation numbers of all atoms and ions in a ion is equal to the charge
What is a half cell/ electode
A strip of metal dipped into a solution of its own ions
DirectionFlow of electrons in batteries
Flow from more reactive metal to less reactive metal
How are two electrodes connected to mearsure the voltage between them
2 metal rods are connected with wires and a high resistance voltmeter, 2 beakers of electrolyte ( positive ions dissolved into the solution with a metal strip in that collects the electrons giving it a negative charge ) are connected with a salt bridge to complete the circuit
What’s a salt bridge and why is this substance suitable
Glass tube or porous material soaked in KNO3 solutions.
It is unreactive with the electrodes and the ions are free to move
What is the role of the voltmeter in connected half cells
Prevents electrons from flowing enabling voltage to be mearsures, Without it electrons will flow from left (most reactive metal) to right (least reactive metal)
Which side does reduction take place on in a cell
Positive right reduced
What electrode to use when there is no solid metal in reaction
Platinum electrode as a metal rod needed from another unreactive metal which aslo conducts electricity
For example if metal ions of 2 differnet charges in solution Fe2+ and Fe3+ which void be made from dissolving Fe2(SO4)3
Essential conditions of standard hydrogen half cell
H2 gas pumped in at 100kPa
Electrolyte contains H+ ions of conc 1moldm-3
Platinum electrode
298K
Voltage on standard hydrogen half cell
0V
Purpose of standard hydrogen electrode
If another electrode is connected up to the standard hydrogen electrode and voltage between them is measured then the voltage on the meter must be of the other electrode
Conventional cell representation of Zn and Cu metal rods
Zn(s)|Zn2+(aq)||Cu2+(aq) | Cu(s)
What does the vertical solid line and double solid line represent in conventional cel representation
One - Indicates a phase boundary
Two - salt bridge
Which species should be written closest to salt bridge
Species with highest oxidation state
Cell representation of standar hydrogen half cell
Pt(s) | H2(g) | H+(aq) ||
Identifying the strongest oxidising agent and weakest reducing agent via electrochemical series
SOWR - most positive value
WRSO - most negative value
Using the electrochemical series to calculate Ecell values
More positive - least positive
Determining whether reacting feasible using electrochemical series
If Ecell value is positive
It mean the cell discharges producing a current
Why are conditions important when calculating electrode potentials
If conditions are changed then:
- the equailbrai could shift to the right meaning more metal and less metal ions and electrons, as few electrons the electrode potential would come more positive
- try e equillbira could shift to the left so less metal and more ions and electrons , as more electron present the electrode potential would come more negative
CAUSES A KNOKON EFFECT ON ANY E CELL VALUES CALCULATED AND MAY BR FEASIBLE UNDER SIME CONDITIINS BUT NOT ORHERS
electrodes in lithium ion battery
Positive electrode is made of lithium cobalt oxide and the negative is made of graphite
what happens when the battery is discharged in lithium ion battery
Layer of Li on the negative carbon electrode dissociates to form Li+ and release electrons
At the positive electrode a lithium ion and electron combine with CoO2 from the electrolyte to form Li+(CoO2)-
Overall reaction occurring when the lithium battery is being used
CoO2 + Li ~> Li(CoO2)
Convention cell representation of lithium battery
Li|Li+||Li+,CoO2| Li(CoO2) | Pt
how is a lithium battery reversible
When the battery has run out because either all the CoO2 or Li has been used up it can be connected to a stronger electrical current which forced the reaction back in the reverse direction to recharge
What is a fuel cell
generates electrical current from electrochemical reactions , it uses the energy from the reaction of a fuel cell with oxygen to create a voltage
What is the modern fuel cell
Hyrgogen fuel cells
Using hyrgogen rich fuel like methanol, natural gas and petrol
Advantages and disadvantages of fuel cells instead of fossil fuels
Pros :
- Greater efficiency than burning hydrogen in a combustion engine
- less polluting as water is the only product
Cons:
- h2 is difficult to store
- fossil fuels are combusted to produce the hydrogen which released CO2
Advantages of fuel cell compared to other types of cells
Voltage is constant as fuel and Oxygen is supplied constantly so conc of reactants remain constant
Draw and label a diagram of standard hyrgogen half cell
Google it
Draw a labelled diagram of hydrogen fuel cell
Google it
Half equation and overall equations of hydrogen fuel cell in alkaline solution
At the negative electode:
H2(g) + 2OH-(aq). <-> 2H20(l) + 2e- (oxidation)
At positive electode:
1/2 O2(g) + H2O(l) + 2e- <-> 2OH- ( reduction)
Overall : H2 (g) + 1/2 O2 (g) ~> H2O (l)
Half equation and overall equation of hydrogen fuel cell in acidic solution
Negative electrode :
H2(g) <-> 2 H+(aq) + 2e-
Positive electode:
1/2 O2 (g) + 2 H+ (aq) + 2e- <->H2O(l)
Overall equation:
H2(g) + 1/2O2(g) ~> H2O(l)
