M5 Chapter 23 - Redox and Electrode Potentials Flashcards
(22 cards)
Define oxidising agent.
A species that is reduced in a reaction and causes another species to be oxidised.
Define reducing agent.
A species that is oxidised in a reaction and causes another species to be reduced.
Define oxidation.
Loss of electrons
An increase in oxidation number
Define reduction.
Gain of electrons
Decrease in the oxidation number
What happens in a redox reaction?
Electrons are transferred from one species to another
One element is reduced and another is oxidised.
What are the half equations and ionic equations for:
SnO + Zn –> ZnO + Sn
Sn2+ + 2e- –> Sn
Zn –> Zn2+ + 2e-
Sn2+ + Zn –> Zn2+ + Sn
Define the standard electrode potential.
The e.m.f of a half cell compared with a standard hydrogen half cell measured at 298K with solution concentration of 1 moldm-3 and a gas pressure of 100kPa.
What happens when a rod of a metal is dipped into a solution of its own ions.
An equilibrium is setup between the solid metal and the aqueous metal ions.
Write a half-equation for Zinc (s) to Zinc (II).
Zn(s) <–> Zn2+(aq) + 2e-
Write a half-equation for copper (II) to copper (III).
Cu2+(aq) –> Cu3+(aq) + e-
What is a standard hydrogen half cell made up of? (3)
HCl (1moldm-3)
H2 Gas (100kPa)
Inert Platinum Electrode
Why is a hydrogen half cell used as a standard half cell?
Easy to control its purity and reproducibility.
How to make simple salt bridge?
Soak piece of filter paper in aqueous solution of KNO3.
Why are salt bridges necessary?
To complete the circuit by connecting the two solutions. This enables charge to be transferred between the half cells. They do not react with the electrodes.
Why might you use other standard electrodes occasionally?
Cheaper/easier/quicker to use and can provide just as good of a reference.
Platinum is expensive to use as a catalyst.
If an E° value is more negative, what does it mean in terms of oxidising and reducing power?
Better reducing agent (easier to oxidise)
If an E° value is more positive, what does it mean in terms of oxidising/reducing power?
Better oxidising agent (easier to reduce)
How do you calculate the emd of a cell from E° values?
E° Cell = E° positive - E° negative
When would you use a platinum electrode?
When both the oxidised and reduced forms of the metal are in aqueous solution.
Why is platinum chosen?
Inert and good conductor to complete the circuit.
How would you predict if a reaction would occur?
Take the 2 half equations
Find the species that is being reduced
Calculate its E° value minus the E° value of the species that is being oxidised.
If E° overall > 0.4V, reaction will occur.
