Physical 11: Electrochemistry Flashcards
(50 cards)
What is a half cell?
Also known as an electrode
An equilibrium set up when a metal is dipped in a solution of its own ions
How do you make an electrical cell?
By joining two half cells together
What does the potential difference of an electrochemical cell tell you?
The direction of electron flow in the cell
If the potential difference is positive, it means that the reaction is spontaneous in the direction written in the notation
If the potential difference is negative, the reaction is not spontaneous in the direction written (under standard conditions)
How do you measure potential difference of an electrochemical cell?
Using a voltmeter to connect the two electrodes
What is a salt bridge?
Usually a piece of filter paper soaked in a salt solution
Solution is usually saturated potassium nitrate, potassium chloride, sodium chloride, sodium nitrate, or ammonium nitrate
Why is a salt bridge used instead of a wire?
Because a wire would only transfer electrons, but the salt bridge transfers ions
Describe the standard hydrogen electrode.
Beaker of 1moldm-3 HCl (aq) to supply H+ ions
Hydrogen gas (100kPa) bubbled through the aqueous solution
Platinum wire coated with finely divided platinum to increase surface area for reaction allows electrical contact to be made
What is platinum black?
The platinum wire coated in finely divided platinum used to make electrical contact in a standard hydrogen electrode
What is the standard hydrogen electrode used for?
The potential of the standard hydrogen electrode is zero, so it can be used to compare the emf of other electrodes
What is the symbol for emf in standard conditions?
E°
What is emf?
Electromotive force
The potential difference between a half cell and the standard hydrogen electrode
What are the standard conditions of the hydrogen electrode?
100kPa hydrogen gas
1moldm-3 HCl solution
298K
What is the electrochemical series?
A list of reduction reactions (electrode potentials)
Arranged so that the most negative electrode potentials are at the top and the most positive are at the bottom
Where are the best oxidising agents in the electrochemical series?
Top left
Because they have very positive potentials and so are the best at attracting electrons
Where are the best reducing agents in the electrochemical series?
Bottom right
Because they have very negative potentials and so are the worst at attracting electrons (repel them)
What are the three general rules for IUPAC cell representation?
1) A vertical solid line represents a phase boundary (i.e. between a solid and solution)
2) A double vertical line represents the salt bridge
3) The species with the highest oxidation state is written next to the salt bridge (R O || O R)
Where are the anode and cathode written in conventional cell representation?
Anode is on the left
Cathode is on the right
What is used to make electrical contact if there are no solid species in the half cell?
An inert platinum electrode
Give the cell representation for an aluminium (Al(s)/Al3+(aq)) and copper (Cu(s)/Cu2+(aq)) cell, given that the aluminium cell is the anode.
How do electrons move between two connected electrodes?
From the more negative to the more positive electrode
How do you predict the direction of the half cell reactions?
The more negative of the two will go in the reverse direction
How do you calculate emf?
Cathode potential - Anode potential
When is a cell’s reaction feasible?
If the forward reaction occurs spontaneously under standard conditions
When the electrons move from the anode to the cathode
The emf should be positive
Name three non-rechargeable cells.
Leclanché cells (Zinc/carbon)
Daniell cells (Zinc/copper)
Zinc chloride
