1.7 Oxidation, Reduction And Redox Reactions
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What is oxidation
• The loss of electrons OR • Gain of oxygen (or any electronegative element) • Loss of Hydrogen (or any electropositive element)
What is reduction
• The gain of electrons OR • Loss of oxygen (or any electronegative element) OR • Gain of hydrogen (or any electropositive element)
What is an oxidising agent
Species that gains electrons
What is a reducing agent
Species that lose electrons
What are the half equations and ionic equation for : SnO + Zn —> ZnO + Sn
Half equations • Sn2+ + 2e- —> Sn • Zn —> Zn2+ + 2e- Ionic equations • Sn2+ + Zn —> Zn2+ + Sn
Define oxidation state
A number which represents the number of electrons lost or gained by an atom of that element in a compound (If electrons are lost, the number is positive) (If electrons are gained, the number is negative)
What is the Oxidation state of O in OF2
[O] = +2
What is the oxidation state of H in KH
[H] = -1
What is the oxidation state of Cl in NaClO
[Cl] = +1
Define the term disproportionation
Where in a redox reaction, the oxidation states of atoms of the same element, increase for some atoms but decrease for some atoms
What is the oxidation state of P in PCl5
[P] = +5
What is the oxidation state of N in NH3
[N] = -3
What is the oxidation state of As in AsO4^3-
[As] = +5
What is the oxidation state of Fe in K4Fe(CN)6
[Fe] = +2
Why is 1s2 2s2 2p5 a weaker reducing agent than 1s2 2s2 2p6 3s2 3p6 4s2?
The 2p electron is closer to the nucleus (smaller atom) than the 4s electron. Hence the nuclear attraction is stronger so the 2p electron is lost less easily than the 4s electron
What happens in a redox reaction
• Electrons are transferred from one species to another • One element is oxidised while another is reduced
Why is 2CrO4^2- + 2H+ —> Cr2O7^2- + H2O not a redox reaction
Chromium is oxidised whereas hydrogen remains the same oxidation state (no element is reduced)