Unit 1- Section 11- Electrochemistry + RP8 Flashcards
How many half cells does a cell contain?
two
In a cell, how are the half cells connected?
by a salt bridge
What is a simple half cell composed of?
- a metal (acts an electrode)
- solution of compound (containing the metal)
What happens when two half cells are connected in a circuit?
a voltage will be produced
why is a voltage formed in a zinc- copper cell?
because the zinc has a higher tendency to oxidise to the Zn2+ ion and release electrons than the copper half cell.
Out of copper and zinc, which electrode will the electrons build up on more?
the zinc electrode, it has a higher tendency to oxidise
why is a high resistance voltmeter used?
to measure the maximum potential difference
describe a Daniell cell
a zinc anode placed in 1moldm-3 zinc sulphate solution
a copper cathode placed in 1moldm-3 copper sulphate solution
What is the role of a salt bridge?
it allows ions to move freely, completing the circuit
Usually, what is a salt bridge made of?
filter paper, soaked in potassium nitrate
What process happens at the cathode?
reduction, the metal ions gain electrons to form solid metal atoms
What process happens at the anode?
oxidation, electrons are generated and flow to the cathode
Over time, what happens to the mass of the anode and cathode?
the anode (reactant) will get used up, and the cathode will gain mass
What is a metal that is commonly used as an electrode, when other metals can’t be used?
platinum, Pt
What does I mean in cell representation?
boundary between different phases
What does II mean in cell representation?
salt bridge
What are two conventional cell representation rules?
-more oxidised species are written closer to the salt bridge (more charged)
- more positive species are written on the right (mostly)
What is a comma used for in cell representation?
it is used to sperate the species in the same phase
What does SHE stand for?
standard hydrogen electrode
What is a SHE used for?
measuring the potential of a half cell
Give the conventional cell representation for a SHE
Pt I H2(g) I H+(aq)
Give the standard conditions for SHE
298K
100kPa
H+ ion containing solution of 1moldm-3
Why is a metal salt bridge not used?
because it would set up its own metal electrode system with the solutions
Why are standard conditions needed for SHE?
Standard conditions are needed because the position of the redox equilibrium will change with conditions. (Le Chatelier’s Principle)
How can standard electrode potentials be written?
as an electrochemical series
What does a more positive EMF value mean?
it will be easier for it to reduce other substances and to act as a reducing agent
What does a more negative EMF value mean?
it will be easier for it to oxidise other substances and to act as an oxidising agent
What is the EMF equation?
Ecell = Ered - Eox
What unit is EMF measured in?
V
