TOPIC 3 - Redox I
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What is oxidation in terms of electrons and oxidation number?
Loss of electrons. Increase in oxidation number.
What is reduction in terms of electrons and oxidation number?
Gain of electrons. Decrease in oxidation number.
What is a redox reaction?
A reaction where there’s both oxidation and reduction taking place?
What happens to oxidising agents in terms of electrons and reduction/oxidation?
They are reduced, so they gain electrons.
What happens to reducing agents in terms of electrons and reduction/oxidation?
They are oxidised, so loose electrons.
What is the rule for oxidation numbers in uncombined elements?
Oxidation number is 0.
What is the rule for oxidation numbers in ions?
Oxidation number = charge of the ion.
What is the rule for oxidation numbers in Group 1?
Always +1
What is the rule for oxidation numbers in Group 2?
Always +2
What is the rule for oxidation numbers in Group 3?
Always +3
What is the rule for oxidation numbers in Hydrogen?
+1 except in hydrides (-1), like in NaH.
What is the rule for oxidation numbers in Chlorine?
-1 except with F and O
What is the rule for oxidation numbers in Fluorine?
Always -1.
What is the rule for oxidation numbers in Oxygen?
-2 except in peroxides (-1) and OF2 (+2)
What should all the oxidation states in a molecule must add up to?
The charge of the molecule
What is a disproportionation reaction?
A reaction where the same species is simultaneously oxidised and reduced.
What are the steps to follow when balancing half equations?
• Write species in the equation. • Balance atoms. (apart from H and O) • Balance any oxygens with H2O • Balance any hydrogens with H+ • Balance charges with electrons.
How do you combine already balanced half equations into a whole equation?
Multiply equations so that they have the same number of electrons. Combine equations and eliminate electrons.