Oxidation and reduction Flashcards
What were reactions that involved the addition of oxygen to a substance described as before the discovery if electrons?
Oxidation reactions
What was removing oxygen from a substance (before the discovery of electrons)
A reduction reaction as the mass of the substance got smaller due to the oxygen being removed.
What did scientists notice after the discovery of the electron?
That many chemical reactions involved the transfer of electrons.
What is meant by many chemical reactions involved the transfer of electrons
One substance lost electrons while another gained electrons.
Define oxidation
Occurs when the element loses electrons.
Define reduction
Occurs when the element gains electrons.
What is a useful way of remembering oxidation and reduction?
OIL RIG - oxidation is loss, reduction is gain.
Do oxidation and reduction occur at the same time?
Yes.
What is the name of the reaction that occurs when one element loses electrons and another element gains electrons?
Redox reactions.
Mg + O –>
Mg(2+) + O (2-) (Mg loses 2e, O gains 2e)
Zn + Cu (2+) –>
Zn (2+) + Cu
Zn is being oxidised = reducing agent
Cu is being reduced = oxidising agent
What is the element that loses the electrons called?
The reducing agent
What is the element that gains electrons called?
The oxidising agent
In the following equation pick out the species being oxidised, the species being reduced, the oxidising agent and the reducing agent = Fe(2+) + Cl –> Fe(3+) + Cl(-)
Fe = oxidised Cl = reduced Fe = the reducing agent Cl = the oxidising agent
What side are the species being oxidised/reduced and the oxidising/reducing agent always on and why?
- Left
- As they are reactants
What is a more useful way of keeping track of the movement of electrons?
By using oxidation numbers
Define oxidation number
The charge an element has or appears to have when it is in a compound when certain rule are applied
What type of bonding do we have to pretend that all compounds have in order to use oxidation numbers?(even thought its not true)
Ionic bonding
What is done for the purpose of pretending that all compounds are ionic?
- The less electronegative element becomes positive (loses electrons)
- The more electronegative element becomes negative (gains electrons)
What is rule 1 for oxidation numbers?
Simple elements i.e those that are not with any other elements, have an oxidation number of zero. (eg Na, Mg & Fe)
What is rule 2 of oxidation numbers?
In the combined state, Group 1 elements always have an oxidation number of +1 and Group 2 elements always have an oxidation number of +2.
What is rule 3 of oxidation numbers?
In simple ions i.e single elements ions, the oxidation number of the ion is equal to the charge on the ion.
What is rule 4 of oxidation numbers?
The halogens, (Group 7) in compounds where the halogen is bonded to one other element, has an oxidation number of -1, unless the halogen is bonded to a more electronegative element, then the oxidation number of the halogen will be +1. ( doesn’t work for halogens in complex ions)
What is rule 5 of oxidation numbers?
Oxygen usually has an oxidation number of -2: except in the compound OF2 it is +2 as F is more electronegative element than O and in the peroxide ion [O2 2-] where O has an oxidation number of -1.
What is rule 6 of oxidation numbers?
Hydrogen has an oxidation number of +1 in its compounds : except when it is combined to an element less electronegative than it because then it is a hydride and has an oxidation number of -1.
What is rule 7 of oxidation numbers?
In complex ions i.e where more than one element is in the ion, the oxidation numbers must add up to the charge on the ion.
What is rule 8 of oxidation numbers?
In neutral molecules the oxidation numbers must add up to zero.
Oxidation (in terms of oxidation numbers)
Oxidation is an increase in oxidation number.
Reduction ( in terms of oxidation)
Reduction is a decrease in oxidation number
