Electrochemistry Flashcards
Explain the function of a salt bridge (2 marks)
The ions in the ionic substance in the salt bridge move through the salt bridge
to maintain charge balance and complete the circuit
Which side is the anode and which side is the cathode. Which one is positive and which one is negative?
Anode = left hand side = negative electrode
Cathode = right hand side = positive electrode
What factors effect the E.M.F of the cell?
- the material of electrodes
- electrolyte used in the cell
- concentration of the electrolyte
- temperature
- partial pressure (for gaseous electroylyte)
La chatlier principle is applied for conc, temperature and pressure
It is independent of shape of electrodes, distance between electrodes and the amount of electrolyte.
How is current made in an electrochemical cell
- There are two processes happening in a cell: oxidation and reduction.
- One metal is oxidised and gives up electrons.
- In the other side of the cell, the other metal accepts these electrons.
- The electrons travel from one side of the cell to the other via the wire, which is the electrical current.
How can you tell whether a reaction is feasible or not?
- If the standard cell potential is positive, the reaction is feasible.
- If the standard cell potential is negative, the reaction is NOT feasible.
What is electromotive force (e.m.f)?
Difference between the two electrodes
What is the Standard Hydrogen Electrode?
- reference point for all potential measurements at all temperatures
- Hydrogen gas is bubbled into a solution containing hydrogen ions with a platinum electrode
What are the standard conditions for Standard Hydrogen Electrode (SHE) (4)
- 100kPa
- 298K (room temperature)
- concentration 1 moldm-3
- zero current
Why is platinum electrode typically used for SHE
because it is inert
What are fuel cells?
Fuel must constantly be supplied (for example hydrogen) to react with oxygen and produce electrical energy.
The cell e.m.f. is constant because the supply of reactants is constantly fed in.
What are the major advantages of using a fuel cell?
converts more of the available energy from the combustion of hydrogen into kinetic energy of the car
Wastes less heat energy than an internal combustion engine
constant supply of energy
doesn’t need recharging
water is its only waste product
Draw a diagram to show how the e.m.f of a hydrogen-oxygen fuel cell changes with time
Suggest why the use of a hydrogen-oxygen fuel cell might not be carbon neutral
CO2 i released because fossil fuels are burned to produce electricity to generate hydrogen
CO2 is released when methane reacts with steam to produce hydrogen
How does the alkaline hydrogen-oxygen fuel cell work?
- The hydrogen gas is delivered to the negative electrode (made of platinum) where it reacts with the hydroxide ions. The half equation for this reaction is: $2H_2(g)+4OH^- = 4H_2O +4e^-$
- The electrons flow through the platinum electrode and this flow of electrons is used to power something
- Oxygen is delivered to the positive electrode and reacts with water: $O_2(g) +2H_2O +4e^- → 4OH^-(aq)$
- The hydroxide ions made from oxygen travel to the negative electrode (made of platinum).The hydroxide ions travel through thesemi permeable membrane, carried by the electrolyse (KOH solution)to the negative electrode where they react with the hydrogen atoms and oxidation occurs. The cycle repeats itself.
What happens if 2 gases are want to measured.
They are bubbled through the solution so it it in contact with the electrode
Draw electrochemical cell for hydrogen and copper
What side of the electrochemical series are reducing agents and why?
On the right hand side has from the right to the left of the equation the species is losing electrons. For example Li is the reducing agent because if you read the equation backwards its losing electrons (which would be gained and hence reducing something else)
What are the simplified electrode reactions in a lithium cobalt cell?
