Redox Reactions Flashcards
What is the reaction for magnesium reacting with oxygen?
Mg (s) + 0.5O2 (g) -> MgO (s)
What is the structure of magnesium oxide?
In has a giant structure consisting of magnesium ions Mg2+ and oxide ione O2-
How is magnesium oxide formed regarding ion transfer?
Two electrons are transferred from the outer shell of the magnesium whicb gives a stable noble gas configuration to form Mg2+. The oxygen atom gains the two electrons to form O2-, which also has a stable noble gas configuration
What are the two half equations for the formation of magnesium oxide?
- Mg -> Mg2+ + 2e-
* 0.5O2 + 2e- -> O2-
How can you get the full equation from half equations?
You add them together
Whatbis oxidation?
The loss of electrons
What is reduction?
The gain of electrons
What are redox reactions?
When one reactant is oxidised and the other is reduced
What does OIL RIG stand for?
Oxidation is loss
Reduction is gain
What are oxidising agents?
The reactant that does the oxidising. They are electron acceptors and are themselves reduced
What is the reducing agent?
The reactant that does the reducing. They are electron donors and are themseleves oxidies
In this equation Na + 0.5Cl2 -> NaCl which reactants are oxidised and reduced and so which are the oxidising and reducing agents?
- Na: oxidised so is the reducing agent
* Cl2: reduced so is the oxidising agent
What are the rules for constructing half equations?
- Write down the formulae of the reactants and products
- Balance any atoms that are not hydrogen or oxygen
- Add H2O to balance oxygen atoms
- Add H+ ions to balance hydrogen atoms
- Balance charges by adding electrons
- (Add state symbols)
- Check equation by writing the oxidation numbers and number of electrons
What are the rules for combining half equations?
- Write down the two half equations
- multiply if necessary to balance electrons
- Add together the two half equations
- Cancel e-, H20 and H+ where necessary
- Check atoms and charges balance
- Add state symbols
In sodium chloride what is the oxidation state for sodium and chlorine?
Sodium has the oxidation state +1 and chlorine has the oxidation state -1
What are the IUPAC rules for assigning oxidations states (oxidation numbers)
1) the oxidation state of a free (uncombined) element is always zero
2) for a simple monatomic ion the oxidation state is the charge on the ion
3) hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2 in most compounds. The exceptions are hydrogen in hydrides of active metals which has an oxidation state of -1 and oxygen which has an oxidation state of -1 in peroxides (e.g. H2O2)
4) the sum of the oxidation states of all atoms in a neutral molecule must be zero.
5) For ions the sum of the oxidation states of the constituent atoms must equal the charge on the ion
How is the oxidation state of an element in a particular compound with more than one oxidation state shown?
By Roman numeral in brackets after the element in the chemical name. There is no space between the bracketed Roman numerals and the element is described:
E.g. iron(II) sulfate with iron having an oxidation state of +2
What is an oxyanion?
It is made from atoms of two elements, one of which is oxygen
Where is much less consistent in the use of variable oxidation states ( roman numerals)?
Non-metals e.g. CO is always called carbon monoxide rather than carbon(II) oxide
What are oxyanions containing chlorine called?
Chlorates
How can oxidation states be used to define oxidation and reduction?
- oxidation occurs when the oxidation state of an element in a reaction increases
- reduction occurs when the oxidation state of an element in a reaction decreases
In the reaction between hydrogen and oxygen what happens with oxidation and reduction?
Hydrogen is oxidised because its oxidation state increases from 0 to +1, while oxygen is reduces because its oxidation state decreases from 0 to -2. To make the equation balanced, for one oxygen being reduced from 0 to -2, two hydrogens must be oxidised from 0 to +1 so it is H2O
What are redox equations also called and what do they show?
They are also called ionic equations. They show what is oxidised and what is reduced in a redox reaction. They do not include ions that are unchanged and present before and after the reaction
For redox reactions how do we work out the overall redox equation?
- By combining the oxidation and reduction half equations
* by seperating the full balanced equation into it’s ions and then removing the spectator ions
