Redox Flashcards
Ammonia + water ->
ammonia hydroxide - which is an alkali
ammonia is a base
Describe what is meant by oxidation in terms of oxygen, hydrogen and electrons
Oxidation - when oxygen is added to a substance
e.g. mg has been oxidised to form MgO
Gain of oxygen
Oxidation of methanol to methanal (H has been removed from methanol)
Removal of hydrogen - oxidation
Oxidation - Loos of electrons
Describe what is meant by reduction in terms of oxygen, hydrogen and electrons
Reduction - loss of oxygen
ZnO has been reduced to Zn
Gain/addition of hydrogen - reduction
(methanal reduced back to methanol - H gained)
When a substance gains electrons - Reduction
What is a spectator ion
Ions that do not change are called spectator ions
e..g if mg2+ ion in reaction does not change it is a spectator ion
What is a redox reaction
Reaction where oxidation and reduction has taken place
electrons are transferred from one chemical to another in a redox reaction
Describe what is meant by an oxidising agent and a reducing agent
Identify the oxidising and reducing agent in the equation
Explain your answers
ZnO + Mg -> Zn + MgO
Oxidising agent - the chemical accepting electrons is called the oxidising agent
Zinc ion is the oxidising agent - as it is accepting electrons from the magnesium atom
Reducing agent - The chemical which is donating the electrons is called the reducing agent
The magnesium atom is the reducing agent as it is donating electrons to the zinc ion
Oxidising agent is reduced
Reducing agent is oxidised
reducing agent reduces another species (carries out reduction)- so it is oxidised
Determine the oxidation numbers/states of elements in a compound
Oxidation states tell us about how electrons are lost or gained in a reaction
if atom has lost electrons - then it will have a positive oxidation number
since mg atom lost two electrons to form the mg 2+ ion - the magnesium has the oxidation number +2 in the magnesium ion
pure element - oxidation state is 0
e.g. Fe, Na, Cl2, O2, S8
when elements have chemically reacted with other elements, then their oxidation numbers will no longer be 0
when reacted F always has oxidation state of -1
Most electronegative element
so no other element can remove an electron from F
O -2 ( is -1 in peroxides and +2 when reacted with Fluorine) F is electronegative enough to remove e- from oxygen
CL, Br, I (-1 = can be positive when bonded to F or O_
H +1 (-1 in metal hydrides e.g. LiH)
Group 1 metals - always +1
group 2 metals - +2
when aluminium react it has an oxidation state of +3
Transition metals - variable
Oxidation states of transition metals can vary depending on the compound
In the case of transition metals, we need to calculate the oxidation state by looking at the oxidation states of other elements in the compound
all of the oxidation states of atoms in a compound must add up to 0
molecule has overall charge of 0
Ion Manganate (VII)
MnO4-
explain why it is called this
The roman numeral tells us the oxidation state of the manganese - which is +7
e.g. in chlorate (I)
ClO- +1 oxidation state
since o2 is more electronegative than chlorine - it can remove electrons from the chlorine atom
Uses of oxidation states in equations
oxidation numbers can be used to work out which chemical is oxidised and which chemical is reduced
if (mg) oxidation number has increased from 0 to +2
When the oxidation number increases, this shows oxidation has taken place
in chlorine - its oxidation number has decreased from 0 to -1
When the oxidation state decreases, this shows that reduction has taken place
acid base reaction - not redox
What is dispropotionation
When atoms of an element in the same species are oxidised and reduced - it is called disproportionation
Cl2 + H2O –> HCL + HCLO
example of what process
Chlorine is reduced from 0 to -1
Chlorine is oxidised from 0 to +1
Therefore disproportionation
