What are oxidising agents?
Accepts electrons (so it reduces itself)
Whats reducing agent?
Donates electrons (so oxidises itself.)
How to construct a redox equation from a half equation?
Combine 2 half equations together:
1- multiply half equations by a factor so number electrons are same in both
2- add 2 half equations together
3- electrons should cancel out leaving redox reaction
(See revision book for example)
How do you construct redox equation from oxidation numbers?
Total increase in oxidation number = total decrease in oxidation number
1) identify reactant and products from info given
2) balance ONLY elements being oxidised/reduced and identify their total change in oxidation number
3) balance change in oxidation number
(See revision book)
When constructing redox equation from oxidation number what are allowed in acidic conditions and alkali conditions?
In acidic conditions: H+ and H2O are allowed
In alkali conditions: OH- and H2O are allowed
Writing half equations
See revision book
What are redox titrations?
Involves transfer of electrons from a reducing agent to an oxidising agent
What are acidified manganate(VII) titrations ?
Acidified potassiummanganate(VII) is a strong OXIDISING agent
- MnO4 - is self indicating so it changes colour when redox is completed
MnO4 - are purple and when redox titration occurs, Purple MnO4- ions REDUCED to very pale pink.
MnO4- reduced to Mn2+
How are redox titrations normally set up?
With oxidising agent in the burette and reducing agent in conical flask.
(Sometimes other way around but should know from question as less precise volume in conical flask)
What are iodine and thiosulfate titrations used for?
Analysis of:
- copper compound/salt
- household bleach
- a copper alloy
Whats the method for iodine and thiosulfate titrations and what happens?
Thiosulfate ion (S2O3 2-) reduces iodide ions and forms tetrathionate ions (S4O6 2-)
Iodine is a yellow brown colour and when reduced this fades.
Colour of iodine fades gradually making it difficult to decide end point so ad starch indicator to solution containing iodine near the end point. The solution turns blue black if iodine present and just disappears all iodine reacted so iodine has been reduced to iodide ions.
(Calculations in revision book)
Titrations
Strong acid/strong base
Strong acid/weak base
Weak acid/strong base
Weak acid/ weak base
(Need to know what graphs would look like)
