Chapter 23 - Redox and Electrode Potentials Flashcards
What is reduction?
A gain of electrons or a decrease in oxidation number
What is oxidation?
A loss of electrons or an increase in oxidation number
What does the oxidising agent do?
Takes electrons from the species being oxidised
What does the reducing agent do?
Adds electrons to the species being reduced
What happens when potassium manganate is titrated?
MnO4- ions are reduced
Describe the process of a potassium manganate titration
Potassium manganate is added to a burette
Sulfuric acid is added to a conical flask
The end-point of the titration is judged when there is a permanent pink colour change
What happens during an iodine/thiosulfate titration?
Thiosulfate ions are oxidised and iodine is reduced
Describe the process of an iodine/thiosulfate titration
Sodium thiosulfate is added to the burette
Add an excess of potassium iodide to a solution of the oxidising agent in a conical flask
The end-point is when a dark, straw colour is reached
What happens when copper reacts with iodide ions?
A solution of I2 and CuI is formed
How many moles of Cu2+ does one mole of S2O32- produce?
1
What is a voltaic cell?
One which converted chemical energy into electrical energy
What is a half cell?
It contains the species present in one half-equation
What is an ion-ion half cell?
Contains ions of the same element in different oxidation states using an inert metal electrode
What does a half cell consist of?
Typically a metal electrode in a solution of its aqueous metal ions
Which is the negative electrode?
The one where the more reactive metal loses electrons
Which is the positive electrode?
The one where the less reactive metal gains electrons
What is the definition for standard electrode potential?
The e.m.f of a half-cell connected to a standard hydrogen half-cell under standard conditions
What is the standard electrode potential of a hydrogen half cell?
0v
How do you measure the standard electrode potential?
Two electrodes are connected by a wire to allow the transfer of electrons
The two solutions are connected by a salt bridge which allows ions to flow
What does a very negative standard electrode potential indicate?
The greater the tendency to lose electrons and undergo oxidation
The metal is more reactive
What does a very positive standard electrode potential indicate?
The greater the tendency to gain electrons and undergo reduction
The metal is less negative
How do you calculate the standard electrode potential of a cell?
The potential of the positive electrode - the potential of the negative electrode
When ordering various electrode potentials from most negative to most positive, where will you find the strongest reducing agent?
The top left
When ordering various electrode potentials from most negative to most positive, where will you find the strongest oxidising agent?
The bottom right
When will the oxidising system on the left of an equation react?
When there are redox systems with a more negative electrode potential
What are the limitations when considering electrode potentials?
The reaction might be feasible, but have a high activation energy with a very slow rate
The conditions might not be standard
Don’t apply to equilibria or solutions that aren’t aqueous
What are primary cells?
Non-rechargeable
Can only be used once
How is energy produced in primary cells?
Oxidation and reduction at the electrodes
What are secondary cells?
Rechargeable cells - the reaction can be reversed
How do fuel cells produce energy?
The fuel and oxygen flow into a cell and the products flow out. This type of cell can operate continuously
