Electrochemistry Flashcards
Answer is A
Although equation 1 is oxidised and needs to be flipped it’s emf still stays the same
E(right) - E(left) = Emf
= 0.34 - -0.44 = 0.78
What happens when you dip a rod of a metal into its own ions
An equilibrium is set between the solid metal and aqueous metal ions
Write the half equation for Zinc (s) to Zinc (ii)
What is the simplest salt bridge made of
Filter paper soaked in a saturated solution of KNO3
Why are salt bridges necessary
To complete the circuit by allowing ion movement between the half cells to balance the charges, without reacting with the electrodes or aqueous metal ions within each half cell
What does a ______ Represent
1) |
2) ||
1) Phase change (solid liquid gas)
2) Salt bridge
How would an aluminium copper cell be represented
In electrochemistry what happens at the left hand electrode
Left hand electrode is where oxidisation occurs
Left hand electrode is the half cell with the most negative E Cell value
In electrochemistry what happens at the right hand electrode
Right hand electrode is where reduction occurs
Right hand electrode is the half cell with most positive e cell
Draw the standard hydrogen Electrode
What conditions is the standard hydrogen electrode used in
Temperature = 298K
Pressure = 100KPA
[H+] = 1 MOLDM^-3
What is the standard hydrogen electrode used for
Universal standard for the Comparing of other cells against the E Cell of the standard hydrogen electrode
E cell of standard hydrogen electrode e= OV
Why might the standard electrode not be used
Cheaper to use another comparison then the SHE
As SHE has platinum
Provides just as a good reference
If an E Cell is more negative what does it mean
Better reducing agent (easier to oxidise)
If an E Cell is more positive what does it mean
Better oxidising agent (Easier to reduce)
What factors alter E Cell value
Concentration of ions
Temperature
What happens if you reduce the concentration of the ions in the left hand half cell
Equilibrium moves to the left to oppose the change of removing ions (in reduced form)
This releases more electrons
the E Cell of the left hand cell becomes more negative
So EMF increases
How do you calculate the emf from e cell value
E Cell = ERight - ELeft
When would you use a platinum electrodes
Why is it chosen
When both oxidised and reduced forms
of the metal are in aqueous solution (no solids)
Inert and a good conductor
How would you predict if a reaction would occur
Take 2 half equations
Find species that is being reduced (RHS electrode)
Calculate its e cell - the e cell of the oxidised species
If E Cell > 0 reaction will occur
What is the Daniel Cell made from
Zinc/Copper(II)
What is the cell for disposable batteries made from
Zinc/Carbon
What reactions take place in a disposable battery
2NH4+ + 2e- ——> 2NH3 + H2
What reactions occur in a lead acid batter (Car Battery)
What reactions occur in Nickel/Cadmium Cell Electrodes (AA Batteries)
(1st one is at net electrode)
What reactions occur on discharge in Lithium Ion Cells
What is a Fuel Cell?
A Chemical Cell that is used to generate electrical current
but does not require electrical charging
a constant supply of a fuel is needed
What are the Reactions that take place at the two electrodes in an alkaline fuel cell
Draw a diagram of a hydrogen fuel cell
Why is it better to use a fuel cell then to burn H2 in air
Even if the same reaction occurs
Combustion requires higher temperatures
Sulphur containing compounds (SO2,SO3) and nitrogen containing compounds (NOx,NO2) are produced due to the sulphur and nitrogen within the atmosphere and high temperatures
These are pollutants
Fuel Cells are more efficient
What are the Disadvantages to hydrogen fuel Cells
Hydrogen is a flammable gas with a low boiling point —> Hard, dangerous and expensive to store and transport as pressurised containers are needed
Energy is required to form the hydrogen and oxygen in the first place. Fossil fuels are used to pass water through an electrolysis process. This contributes to CO2
What are the Advantages to Fuel cells
More efficient then ICE, more energy converted to kinetic then thermal store
Fuel cells don’t require to be charged unlike EV’s
Only waste product is water
How do you find the weakest reducing agent
Most positive E Cell value
Product of the reduced form
This reaction has the highest tendency to gain electrons, a reducing agent must loose electrons in an attempt to reduce a substance. Therefore it is the weakest
How do you find the Weakest Oxidising agent
Most Negative E Cell value
Reactant of the reduced form
This reaction has the highest tendency to loose electrons, a oxidising agent gains electrons in an attempt to oxidise a substance.
Therefore the oxidising agent gains the least amount of electrons
Weakest
How do you find the most powerful oxidising agent
Most positive E Cell value
Reactant of the reduced form
This reaction has the highest tendency to gain electrons, a oxidising agent must gain electrons in an attempt to reduce a substance. Therefore it is the strongest
How do you find the most powerful reducing agent
Most negative E Cell value
Product of the reduced form
This reaction has the highest tendency to loose electrons, a reducing agent must loose electrons in an attempt to reduce a substance. Therefore it is the Strongest.
What is the reason some cells cannot be reachrged
The reaction of the cell isn’t reversible, products cannot be converted back into reactants
How can the emf of a cell be kept constant
Reagents are supplied constantly so the concentrations of ions are constant
Hence the electrode potential difference (E Cell( between the cells is the same
What is the overall Equation of discharge in a lithium ion cell?
Negative Electrode = -3.04 v
Positive Electrode= +0.56v
What is the E Cell
0.56 (Right) — -3.04(Left) = 3.60v
What reactions occur at a acidic hydrogen oxygen fuel cell?
What is the emf of an acidic and alkaline hydrogen oxygen fuel cell
1.23v
What does Acidify mean
Reduced, gained electrons
A List of electrode Potentials (E Cell) in Numerical Order
From the Table Below
Write an Equation for the reaction between VO2 + and iron to form VO (2+)
Non Standard Conditions
How do you maintain a Constant Emf in a Fuel Cell
Reactants must be constantly supplied at the same rate
Stage 1:
Creation of 1 MolDm^-3 of TIO^2+
0.5 moldm^-3 of H2SO4 in 50ml = 0.05moldm^-3 of H+ ions
Therefore 0.05X159.9 = 7.995g needs to be weighed of TiOSO4
And added to the Sulphuric Acid
Transfer to Volumetric Flask and make up to mark
Stage 2:
Place titanium solid electrode immersed into the 1moldm^-3 of acidified TiO2+
Connect this half cell with a salt bridge to the copper half cell and place the titanium half cell on the left
Connect Electrodes with a high resistance voltmeter
Stage 3:
Record table of values of true emf of the cell
Emf = ERHS - ELHS Emf = ECopper=ETitanium
If average emf = 1.22v then this shows the E cell foe the titanium half cell is -0.88v
When creating a half cell: What conditions have to be met?
- electrode immersed in 1 MolDm^-3 of aqueous ion in solution
- 298K
For copper to react it needs to be oxidised
For this reaction to be feasible EReduced - EOxidised >0
most acids e cell = 0.00 , 0.00<0.34, ECell = -0.34 not feasible
Nitric Acid e cell = 0.93, 0.93>0.34 , ECell = 0.62 Is feasible
Explain how you work out the overall equation of a Cell
Write half equations that is happening at the positive and negative electrodes
make sure negative is in its oxidised form
Equate the amount of electrons on either sides by multiplying
Combine reactants and products either side of the —->
Cross out anything thats on both sides
What is the Function of the Porous Seperator
Allows ion movement between half cells
Completes the circuit
Acts as a salt Bridge
Explain why for a half cell connected to a lamp, does the potential difference eventually reach 0
The LHS gains positive charge as electrons are lost while the RHS looses positive charge as electrons are gained
Eventually potential difference between the two half cells becomes 0, and the concentration of ions in both half cells are equal
The half equations for a glucose-oxygen cell at the negative and positive electrodes are given respectively.
Give the conventional Representation of the Glucose Oxygen cell
Negative extrude has a carbon electrode
Positive electrode has a platinum Electrode
