Chapter 23 - Redox and Electrode Potentials Flashcards
(28 cards)
What is meant by oxidation?
Loss of electrons
Or increase in oxidation number
What is meant by reduction?
Gain of electrons
Or decrease in oxidation number
What must a redox reaction always contain?
An oxidising agent
A reducing agent
What is the oxidising agent?
Takes electrons from the species being oxidised
Therefore it contains the species that is reduced
What is the reducing agent?
Gives electrons to the species being reduced
Therefore it contains the species that is oxidised
What does a half equations ultimately show?
Oxidation or reductions
Has electrons on the RHS of the equation for oxidation and on the LHS for reduction
What happens when you combine two half equations?
Overall redox reaction equation is made
What is important to remember when combining two half equations?
The number of electrons that are transferred are balanced
Why is manganate(VII) used when carrying out redox titrations and analysing different reducing agents?
Is a good oxidising agent
How do we carry out a redox titration?
A standard solution of MnO₄⁻ goes in the burette
Burette readings are taken from the top of the meniscus
A pipette is used to add a measured volume of the solution being analysed to a conical flask
An excess of H₂SO₄ is added
An indicator is not required
The endpoint is judges by the first permanent pink colour
Why are burette readings taken from the top of the meniscus?
As the deep purple colour of MnO₄⁻ makes it difficult to see the bottom of the meniscus
What are the purpose of iodine/thiosulphate titrations?
Provide a useful method for quantitative analysis of oxidising agents
How do we carry out an iodine/thiosulfate titration?
Excess of potassium iodide is added to a sample of the oxidising agent being analysed
All of the oxidising agents reacts
I⁻ ions are oxidised to I₂
Solutions turns yellow-brown
How do we know when iodine/thiosulfate titration reaches the end point?
Appears star yellow
At this point a small amount of starch indicator is added
Why do we add a small amount of starch close to the end point of the iodine/thiosulfate titration?
To help with identification of the endpoint
A deep blue-black colour forms
What is the purpose of the voltaic cell?
Arranges for the two equations to occur separately in haf-cells
What is a half-cell?
Contains the chemical species present in a redox half-equation
What does a half cell look like?
What must occur in order for electrons to flow from one half-cell to the other through wires?
Two half-cells must be joined together
What is the purpose of the voltmeter?
Measures the different in potential between the two electrons (in V) - E꜀ₑₗₗ
What is the purpose of the salt bridge?
Allows ions to flow
An example of an electrochemical cell:
What is meant by standard electrode potential?
Tendency to be reduced and gain electrons
What does a more negative Eᵒ value of the half cell suggest?
The greater the tendency to lose electrons
