3.1 Redox And Standard Electrode Potential Flashcards
What is oxidation and an oxidising agent
Oxidation is loss of electrons.
An oxidising agent is a species that oxidises another species by removing electrons from it. It therefore becomes reduced itself in the process.
What is reduction and a reducing agent
Reduction is gain of electrons.
A reducing agent is a species that reduces another species by donating electrons to it. It therefore becomes oxidised itself in the process.
What is the oxidation state of an element in its standard form
0
Even for diatomic molecules like O2
What must the sum of oxidation states in an ion be
The overall charge of the ion
Which element is a compound is assigned a negative oxidation state
The most electronegative element
What is the oxidation state of group 1 and 2 metals
+1 and +2
What’s the oxidation state of aluminium in compounds
+3
What’s the usual state of hydrogen in compounds
+1 except in metal hydrides is -1
What’s the usual oxidation state of oxygen in compounds
-2 except in peroxides (-1) or when bonded to fluorine it’s positive
What is the usual state of chlorine in compounds
-1 except in compounds bonded with oxygen and fluorine where its positive
How can you tell if a species has been oxidised or reduced during a redox reaction
If the oxidation state of an element in a species becomes more positive, that species has been oxidised during the reaction.
If the oxidation state of an element in a given species becomes less positive, that species has been reduced during the reaction.
What is the metal/metal ion half cell
The metal / metal ion half-cell. It consists of an electrode made of the metal dipped into a 1 moldm ^-3 solution of the metal ions.
Describe a solution half cell
This half-cell is used when an element in an aqueous ion is oxidised or reduced to form a different aqueous ion. It consists of a solution made up of both the oxidised and reduced form, both of concentration 1 moldm-3 and an electrode made of platinum and coated with very fine platinum powder (known as platinum black).
Describe the gas half cell
This half-cell is used when either the reduced or oxidised species in a half equation is a gas and the other species is an aqueous ion. It is made up of a 1 moldm -3
solution of the aqueous ions associated with the gas, a platinum black electrode dipped into the solution, and glass cover over the platinum electrode that surrounds the electrode in a steady stream of the gas kept at a pressure of 1 atmosphere (1 atm),
Define a salt bridge
salt bridge could be as simple as a piece of filter paper soaked in saturated potassium nitrate solution ,this allows ions to move between the two solutions and carry electrical energy
Why is potassium nitrate used as a salt bridge
Potassium nitrate is used as almost all potassium compounds and almost all nitrate compounds are soluble in water, and so will not form a solid that could block conduction of electrical energy.
What is the SHE (standard hydrogen electrode)
This is simply a gas electrode that uses hydrogen gas at 1 atm, a solution of H+(aq) ions of concentration 1 moldm
−3
(usually using 0.5 mol dm-3 sulfuric acid), and a platinum black electrode
How do you calculate EMF
E cell. Θ
=E
Θ
(most positive)−E
Θ
(most negative)
Θ
How do you know if a reaction is feasible
E= red- ox
If E is positive, the reaction is feasible
