Redox Flashcards
Oxidation number of a free element
Always zero
Where to add hydrogen and water when doing redox equations?
Add water to the side with less oxygen and hydrogen to the other side (with more oxygen)/side with less hydrogen
Redox rule about oxidation number of elements in a compound
Always add up to zero (eg. NaCl… Na + added to Cl- gives 0)
Redox rule about oxidation number of monoatomic ions
Oxidation number equals charge (eg. Zn 2+ has an oxidation number of 2+)
Redox rule about oxidation number in a polyatomic ion
The sum of the individual oxidation numbers of the ions adds up to the charge of the whole ion. (Eg. CO3 2-, C has oxidation number of 4, O has oxidation number of -2, three lots of O makes oxidation number -6, then add this to 4 to make -2, this number is also the charge of the whole ion because it’s CO3 NEGATIVE TWO)
Name the elements which have oxidation numbers which are their charges
All group 1 & 2 metals
FOBIACH
Fluorine
Oxygen (except in peroxide’s like H2O2 [a peroxide is a compound with two oxygens in it] when the oxidation number is 1- AND when bonded to more electronegative fluorine its oxidation state can vary depending on the compound it’s in and what it’s bonded to)
Bromine (except in compounds with oxygen and fluorine)
Iodine (except in compounds with oxygen and fluorine)
Aluminium
Chlorine (except in compounds with oxygen and fluorine)
Hydrogen (except in metal hydrides [a metal hydride is a metal bonded to a hydrogen eg NaH] when the oxidation number is -1)
Disproportionation
Element in a single species simultaneously becomes oxidised and reduced.
Disproportionation reaction example explain : CL2 + H2O —> HCLO + HCL
Cl in CL2 goes from oxidation state of 0 to +1 in HClO (because HCLO -2 + 1 + 1 which adds to 0. It’s oxidised.
Cl in CL2 goes from oxidation state of 0 to -1 in HCL (because HCL has 1+ of H so must add -1 to get to 0) It’s reduced.
Disproportionation practice Q :
3CL 2+ 6OH- —> CLO3- + 3CL- + 3H20
How and what element disproportionates?
Chlorine
0 to +5 (oxidation)
0 to -1 (reduction)
Definition of oxidation in terms of electron transfer and oxidation number.
Oxidation is when the element loses electrons and the oxidation number increases.
Definition of reduction in terms of electron transfer and oxidation number.
Reduction is the gain of electrons and when the oxidation number decreases.
Oxidising agent definition
Oxidising agent is something that oxidises another species (causing the other species to lose electrons). These electrons which are lost are gained by the oxidising agent which in turn becomes reduced.
Reducing agent definition
The reducing agent is something that reduces another species which causes this species to gain electrons. These electrons that it gains are the same electrons that the reducing agent has lost.
Redox reaction definition
Occurs when one species is reduced and ANOTHER species is simultaneously oxidised. In any redox reaction, the number of electrons released by the oxidation reaction must be the same as the number of electrons used by the reduction reaction.
Why is chlorine a stronger oxidising agent than bromine?
Chlorine is a stronger oxidising agent than bromine because it is able to gain an electron more readily due to its smaller atomic radius, less shielding and greater electrostatic force of attraction.
