Redox Flashcards
What can the process of oxidation and reduction be expressed in terms of
Electron transfer
Oxidation
Loss of electrons
Reduction
Gain of electrons
Where do oxidation and reduction occur
Together in a redox reaction
Half equations
Seperate equations showing oxidation and reduction processes
What must a half equation be balanced in terms of
Atoms and charge
Oxidation state
Number of electrons involved when an atom forms a bond
What does oxidation state refer to
One atom of the element in a compound or ion
What does the oxidation state have
A number and a sign
What does an uncombined element have
An oxidation state of zero
What is the oxidation state of group one elements in compounds
+1
What is the oxidation state of group 2 elements in compounds
+2
What is the oxidation state of group 3 elements in compounds
+3
What is the oxidation state of hydrogen in compounds
+1
What is the oxidation state of fluorine in compounds
-1
What is the oxidation state of oxygen in compounds
-2
What is the oxidation state of chlorine in compounds
-1
What is the exception to the oxidation state rule of hydrogen in compounds
Hydride ions have an oxidation state of 1-
What are the exceptions to the rule of oxidation state in oxygen in compounds
With fluorine/peroxide ions
What are the exceptions to the oxidation state rule in chlorine in compounds
With oxygen
What is the rule for oxidation state in compounds
The oxidation state of each atom in the compounds formula counts separately and the numerical sum is zero
What is the oxidation state rule for an element existing as an ion
The oxidation state is the charge on the ion
What is the oxidation state rule for compound ions
The sum of the oxidation states of the atoms is the charge on the ion
What are Roman numerals in chemical names used to indicate
The oxidation state of the appropriate element
E.g. Iron (II) oxide- metals oxidation state +2
What can we work out by assigning oxidation states
Which species have been oxidised and which reduced without writing half equations
Oxidation (OS)
Increase in oxidation state
Reduction (OS)
Decrease in oxidation state
What must occur in a redox reaction in order to cause the loss of electrons from one species
Another species must accept the electrons
What is the species that accepts electrons and causes oxidation called
An oxidising agent
In order for a species to gain electrons in a redox reaction what must occur
Another species must donate electrons
What is the species that donates electrons and causes reduction called
Reducing agent
Oxidising agent
Species that accepts electrons
Reducing agent
Is a species that donates electrons
What must you make sure balance when writing half equations
Atoms and charges
What is the first step in constructing complex half equations
Write down the formulae for the reactants and products and balance the atoms undergoing redox
How to balance oxygen atoms in half equations
Add water to side with least oxygen
How to balance hydrogen atoms in half equations
Add h+ ions to side with least hydrogen
How to balance the charges in half equations
Add electrons to most positive side
What must each equations show when combining half equations
One side must show reduction and the other must show oxidation
What must the number of electrons being transferred be when combining half equations
The same- you may have to multiply one or both of the half equations
Which species must be cancelled when combining half equations
Any species that appears on both sides
