Redox Flashcards
what is an oxidation number
- Oxidation number is the “formal charge” on an atom.
- It is the charge the atom would have if all the bonds were 100% ionic bonds.
- It is a measure of the number of electrons that an atom uses for bonding.
Name some species and their oxidation number:
Uncombined element- 0
Combined oxygen- -2
Combined hydrogen - +1
Combined fluorine - -1
Simple ion- Charge on ion
What’s the definition of redox reactions and give an example
- A reaction in which both reduction and oxidation take place
example:
Mg + Cl2 → MgCl2
0 0 +2 -1
Define electrode potential
- a measure of the voltage generated by a half-cell in an electrochemical cell.
what does electrode potential measure/show
- it is a way of measuring/quantifying how readily a metal (or other oxidising/reducing agent) gives up its electron(s) to form the metal ion in solution…
- or how readily an ion will accept an electron to form its element
- Electrode potential measures the potential difference/electromotive force (emf) between two electrodes
describe what happens in a cell with 2 electrodes
- the electrode with the more reactive metal more readily loses its electrons and is oxidised. – negative electrode
- The less reactive metal gains electrons and is reduced. – positive electrode
- This created a potential difference/electromotive force caused by the relative difference in “richness” of electrons.
defien standard electrode potential and how is it calculated
- Standard electrode potential compares the tendency of a metal to form its ion with the tendency of hydrogen to form its ion
- Standard electrode potential = the emf measured when a metal in a solution of its ions is coupled to a hydrogen electrode = Eθ
whats the purpose of the salt bridge
- allows flow of ions between electrodes - makes electrical contact
- e.g. KNO3
whats the purpose of the high resistance voltmeter
measure potential difference without allowing flow of current
why is platinum used in the standard hydrogen electrode
Pt is unreactive and acts a catalyst
what happen sin a standard hydrogen electrode
Hydrogen gas flows over the porous platinum electrode
what are the stnadard conditions for the standard hydrogen electrode
- 100 kPa (1 bar) and 298 K
- H+(aq) at 1 moldm-3
how does negativity of a half equation relate to its oxidation or reduction
The more negative the voltage is, the more likely they are to be oxidises (negative electrode)
how do you calculate the Eθ of a cell
Eθ cell = Eθ red - Eθ oxid
how can you use feasibility to predict the feasibilty of reactions
- If the Eθ(proposed red n) – Eθ (proposed oxid n) = +ive
- if the overall value is positve , then it is feasible,
- if its negative it is not feasible
describe a standard hydrogen electrode
