Topic 14- Redox II Flashcards
What conditions are assumed at the standard electrode potential?
1.0 mol dm-3
100kPa
298K/25c
No current flowing
Reducing agent is itself …….
oxidised
Oxidising agent is itself ……
reduced
Why is a high resistance voltmeter needed?
To stop the current from flowing in the circuit so you can measure the maximum Potential Difference (E)
What is the salt bridge soaked in?
filter paper soaked in KNO3, potassium nitrate
unreactive with electrodes and solutions
The most positive electrode will always undergo ….
reduction
the most negative electrode will always undergo …..
oxidation
When writing cell diagrams, which species are put next to the double solid line?
The most oxidised (inside)
so then the outermost species are most reduced
The more ……. half cell is written on the right
positive
What do the lines represent in a cell diagram?
the salt bridge = I I
Separation of phases e.g. solid and solution = I
What is a , used for in cell diagrams?
Separates species in the same physical state
If a system doesn’t include a metal that can act as an electrode then a ….. electrode must be used.
platinum
What is the reference electrode and what is its potential?
A hydrogen electrode and = 0v
Why do we use a reference electrode?
As to measure the potential difference we need 2 electrodes and must know 1 potential
The potential of all electrodes are measured by comparing their potential to that of the standard ….. electrode
hydrogen
What is the equation for the hydrogen electrode equilibrium?
H2 2H+ + 2e-
When writing half equations the more oxidised is on the ….. and the more reduced is therefore on the …..
The more oxidised = left
The more reduced = right
in the electrode system containing two ………. it is necessary to use a platinum electrode and both solutions must be of a …. concentration.
solutions, 1 mol
How to calculate the EMF of the cell?
Ecell= E(right) - E(left) Ecell= E(reduction) - E(oxidation)
The more …… electrode potential is on the right
positive
The more ……. half cell will always reduce (go forwards)
positive
How do you know which direction to write a half-cell equation in?
Reduction is always forward reaction (left to right) in half-cell equations, electrons always added on LEFT side
Oxidation always happens at the….. and the reduction always happens at the ……
Oxidation = Anode Reduction= Cathode
More reactive metal gives up its electrons and is …. ( becomes the anode where e-‘s flow from) and less reactive metal becomes the cathode
More reactive metals become the anode and is oxidised
When drawing half cells the half-cell where oxidation happens (the ……) should always be on the ……
Oxidation happens = anode = left
When drawing half cells the half-cell where reduction happens ~( the cathode) should always be on the ….
Reduction happens = cathode = right
What is the role of the salt bridge? (2)
The salt bridge completes the circuit (1)
and allows ions to flow between half cells to balance the charges (1)
When calculating the electrode potential the half equation that is more positive E goes …… and the more negative …….
E goes forward if more positive
backwards if more negative
Write an equation with the two half cells:
Zn(aq)2+ + 2e- = Zn(s) -0.76
Cu(aq)2+ + 2e- = Cu(s) +0.34
Cu2+ + Zn(s) == Cu(s) + Zn2+
Define the standard electrode potential?
The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode
The standard H electrode is always found on the ….. (in diagrams)
LEFT
