Oxidation, Reduction And Redox Equations Flashcards
What are redox reactions
They’re where oxidation and reduction occur simultaneously(same time)
What are oxidation states
The oxidation state in a compound is defined as the
Hypothetical/assumed charge in the atom
»When we assume bonding is completely ionic
Oxidation state is a numerical value of degree
Of oxidation or reduction of an atom/element
- non-zero oxidation states =sign + number (eg -3)
What are oxidation states of ions and some general points on oxidation states?
The oxidation state of a simple ion is its charge
Eg..
- iron in Fe3+ = +3
- tin in Sn2+ = +2
GENERAL POINTS..
• total sum of oxidation states of all elements in compound
Equal zero
• total sum of oxidation states of elements in molecular ion
Add up to its charge
•
• maximum oxidation state of an element = group number
• minimum oxidation state of an event = group num - 8
What are some rules for finding oxidation state
• oxygen has an oxidation state of -2 in all compounds
EXCEPT peroxides (-1) and OF2 (+2)
• hydrogen has +1 in all compounds
EXCEPT metallic hydrides (-1)
• G1/2 have oxidation states +1/+2 in all compounds
• oxidation states of transition + p block elements vary
• in simple binary compound (2 element)
More electronegative element =negative oxidation state
• d block elements where ion charge is given (eg. Cu(II))
Copper has oxidation state +2 etc.
Correct names and ion/compound formulae
The correct chemical name for an ion (or part of a compound)
Depends on oxidation state
As for formulae of molecular ions
All molecular ions ending in -te contain d or p block elements
And some oxygen atoms ..
- carbonate ion = one C, some O
- dichromate = two Cr , some O
Some ions have hydrogen too
- hydrogen carbonate
- dihydrogen phosphate
What’s oxidation and reduction
Increase in oxidation state = oxidation
Decrease in oxidation state = reduction
What are examples of redox reactions
Eg. Cl2 + H2O = HCl + HOCl
Cl is oxidised , showing increase in oxidation state in HOCl
Cl is also reduced, decreasing oxidation state in HCl
So hence is a redox
If asked to explain a redox reaction , calculate oxidation states
Then state redox definition
What are oxidising and reducing agents
An oxidising agent is a chemical causing
Oxidisation in another species
- oxidising agents accept electrons (causing another to lose them)
A reducing agent is a chemical causing reduction in another species
- reducing agents lose electrons (giving to other substance)
HLAF EQUATIOS
What are a half equations
Half equations include electrons,
showing oxidation and reduction in chemical reactions
In reduction (gain electrons) half equations..
Sn2+ + 2e- = Sn
In oxidation ((losing electrons) half equations..
Mg = Mg2+ + 2e-
The total change in oxidation state is same
As number of electrons required/needed in equation
- NO3 (oxidation state of N is +5) is reduced to NO (+2)
- total change in oxidation state is +3 so 3e- added
- if O atoms are added or removed, H2O
And H+ balance this
4H+ + 3e- + NO3 = NO + 2H2O
Total of charges on both sides must be zero
What are organic oxidation and reduction reactions
Organic chemicals (primary,secondary alcohols) are
Oxidised by reagents - like acidified potassium dichromate sol.
- primary alcohols (like ethanol) are oxidised to aldehydes
Wch may be further oxidised to carboxylic acids
- ethanol by be oxidised to ethanal then ethanoic acid
- secondary alcohols (propan2ol) may oxidise to ketones
- propan2ol oxidised to propanone
..
Simple oxidation reactions
—> equations for oxidation of organic chemicals
May be written with O representing oxidising agent
- oxidation in organic chem is removal of H atoms
or addition of oxygen atoms
Simple reduction reactions..
—> equations for reduction of organic chemicals
May be written simply using H to represent reducing agent
- reduction in organic chem is removal of O atoms
AND/OR addition of H atoms
What are organic half equations
Organic oxidation and reduction reactions
May also be written as half equations involving electrons
- same procedure is followed as for half equations for
S p and d block elements except oxidation state of elements isn’t determined
How do you combine half equations (and what are ionic eqs)
Ionic equations are the reactions between two ionic
Species transferring electrons (don’t include lone electrons)
- Mg + 2H+ = Mg2+ + H2
- Cl2 + 2I- = 2Cl- + I2
..
When combining, two half equations given (red and ox)
And asked to write the ionic.
- matter of multiplying half equations by a number
wch gives same number of electrons in each
- when equations are added together to make an ionic,
Will be same electrons on each side of ionic (cancelled)
> if H2O or H+ on both sides, can also
cancel down (never completely tho)
Two ways these half equations are presented..
- one reduction, other oxidation
- if birth reduction, one has to be reversed to make oxidation
When combining half equations, how do you add half equations
1- make sure one oxidisation and other is reduction
2- make sure electrons are same amount in both
(multiply whole equation to make equal)
3- to add, write all species on left side of both
And same with right
4- cancel out electrons on both sides
