Electrochemical cells Flashcards
1
Q
What do voltaic cells/galvanic cells do?
A
- They generate electricity from spontaneous redox reactions
- They use redox reactions to produce electric current
- Spontaneous means no external energy source requires
2
Q
Explain the structure of a galvanic cell.
A
- Consists of two half-cells
- They contain an electrode each (metal) and are submerged in a solution of its ions
- Electrodes connected by an external circuit and a voltmeter to measure voltage
- Cell contains a salt bridge that allows ions to complete the circuit and prevent build-up of electric charge, ensure electrical neutrality
3
Q
What is a salt bridge made up of?
A
- Strip of filter paper soaked in saturated potassium nitrate (KNO3), K+ goes to cathode and NO3- goes to anode
- These ions do not react with the other ions present in the two half-cells
- Prevents build-up of electric charge
4
Q
What happens in the galvanic cell when the electrical current is turned on?
A
- The metal atoms of the anode are oxidised, they lose electrons to form metal ions
- At the same time the zinc ions in solution are reduced and gain electrons to from metal atoms
- This results in a state of equilibrium
5
Q
How can an equilibrium be established?
A
- If a rob of metal (electrode) is dipped into a solution of its own ions, an equilibrium is established
- The position of equilibrium determines the potential difference between the metal strip and the solution of metal
- Metal ions from electrode deposit electrons into the solution
- The ions in the solution accepts two electrons and moves to the electrode to become metal atoms
- Potential difference is set up between the electrode and solution –> electrode potential
6
Q
What is potential difference?
A
- Difference in the amount of energy that charge carriers have between two points in a circuit
- The difference in the tendency to either undergo oxidation or reduction between more and less reactive metals
7
Q
Explain the position of equilibrium in regard to the reactivity of the metals.
A
- More reactive metals, have a greater tendency to lose electrons to form positive ions, equilibrium lies to the left
- A less reactive metal has lower tendency to lose electrons, equilibrium lies to the right
8
Q
What metals are oxidised and what metals are reduced?
A
- More reactive metal is oxidised (anode)
- Less reactive metal is reduced (cathode)
9
Q
What is the cell potential?
A
- A.k.a electromotive force (EMF)
- Difference in the electrode potentials of the half-cells in a voltaic cell
- Measured in volts
- Difference in tendency to either undergo oxidation or reduction
10
Q
What type of reaction and change in energy occurs in a voltaic cell?
A
- Exothermic reaction, heat is released
- Chemical energy —> electrical energy
- Separation of two reactions enables the release of electrical energy
11
Q
What does the potential difference (voltage) of a cell depend on?
A
- The nature of the electrodes and the ions involved
- Temperature
- Ion concentrations of the solution
- The further apart the two metals are in the activity series, the higher the voltage produced by voltaic cell
12
Q
Explain the specific example of Daniell Cell?
A
- Anode: zinc (left half-cell zinc sulphate)
- Cathode: copper (right half-cell copper sulphate)
- Salt bridge of KNO3
- Anions flow to the negative half cell, replace the negative charge of the electrons
- Cations flow to the positive half cell (cathode)
Half equations in book
13
Q
How do you draw the cell diagram convention?
A
- Its a shorthand method used to replace a voltaic cell
- Have phase boundary between solid and aqueous solution
- Salt bridge (double line)
- Anode on left, cathode on right
- Spectator ions not included in diagram
Check book
14
Q
What type of electrolyte is used in an electrolytic cell?
A
- Ionic compounds, conduct electricity when molten or dissolved in a solution
- Ionic compound split up
15
Q
What is electrolysis used for?
A
- Purifying copper
- Electroplating metals
- Extracting reactive metals e.g. aluminium
- Making Cl, H and NaOH
