Chapter 23 - Redox and electrode potentials Flashcards
What is an oxidising agent?
A species which oxidises other species and is itself reduced.
What is a reducing agent?
A species which reduces other species and is itself oxidised.
What is a redox reaction?
A reaction containing species which are oxidised and species that are reduced.
What is a redox titration?
A titration in which a solution of reducing agent is titrated with a solution of an oxidising agent.
What are manganate (VII) redox titrations used for?
Acidified manganate(VII) is an oxidising agent and manganate(VII) (MnO^4-) titrations are used for analysing reducing agents.
What are iodine/thiosulfate titrations used for?
Describe the initial process.
Analysing oxidising agents.
The oxidising agent is reacted with an excess of iodide ions (e.g. 2I- found in KI). The iodide ions are oxidised to iodine.
The iodine generated is the titrated with thiosulfate ions, S203^2- (aq), until the solution turns colourless..
What is an assumption made in iodine/thiosulfate calculations?
n(Cu^2+) = n(S2O3^2-)
Cu^2+ is an example of an oxidising agent that can be analysed using iodine/thiosulfate titrations.
What is a half-cell?
A cell which contains the chemical species present in a redox half-equation.
What is a voltaic cell?
A type of electrochemical cell which converts chemical energy into electrical energy.
A voltaic cell can be made by connecting two different half-cells, creating an electrode potential, which then allows electrons to flow.
What is a metal/metal ion half-cell?
A metal rod dipped into a solution of its metal ion.
An equilibrium is set up between the metal ion and the metal.
e.g. Zn/Zn^2+ half-cell:
Zn^2+ + 2e- ⇌ Zn (s)
→ reduction
← oxidation
What is a ion/ion half-cell?
A solution containing ions of the same element in different oxidation states (e.g. Fe^2+ and Fe^3+).
An inert platinum electrode is used to transport electrons into or out of the half-cell.
e.g. Fe^2+/Fe^3+ half-cell:
Fe^3+(aq) + e- ⇌ Fe^2+(aq)
→ reduction
← oxidation
What is electrode potential, E?
What is the unit?
The tendency for electrons to be gained and for reduction to take place in a half-cell.
Unit: V
What is the standard electrode potential?
The e.m.f. of a half-cell connected to a standard hydrogen half-cell under standard conditions (298K, 100kPa, 1 moldm^-3).
The standard electrode potential of a standard hydrogen half-cell under is 0V.
What is the equation for the standard electrode potential of a cell?
E(positive electrode) - E(negative electrode)
How are the standard electrode potentials of half-cells measured?
By connecting to a standard hydrogen electrode.
What are the limitations of feasibility predictions using standard electrode potentials?
Standard electrode potentials only apply to aqueous equilbria.
Standard electrode potentials do not take account of activation energy and rate of reactions.
What is a fuel cell?
A cell which uses the energy from the reaction of a fuel with oxygen to create a voltage.
- Oxygen is at the positive electrode where reduction takes place.
- The fuel is at the negative electrode where oxidation takes place.
What is a hydrogen fuel cell?
A fuel cell which can operate with an acid or alkali electrolyte.
2H+(aq) + 2e- ⇌ H2(g)
O2(g) + 4H+(aq) + 4e- ⇌ 2H2O(l)
Overall cell reaction: 2H2(g) + O2(g) → 2H2O(l)
