23.1 redox reactions + 23.2/3 redox titrations

What is the oxidising agent

takes electrons from the species that is being oxidised

what is the reducing agent

takes electrons from the species being reduced

How to balance equations using oxidation numbers

1. assign oxidation numbers to identify the atoms that changed their oxidation number

2. balance only the species that contain elements that have a change in oxidation number

3. balance any remaining atoms

Manganate (vii) titrations procedure

1. a standard solution of potassium manganate (vii) is added to the burette

2. using a pipette, add a measured volume of the solution being added to the conical flask

3. an excess of sulphuric acid is added to provide the H+ ions

4. carry out the titration and the end point is when the first permanent pink colour is reached

5. repeat the titration until two concordant results are obtained

carrying out an iodine/ thiosulfate redox titration

1. prepare a standard solution of Na2S3O3 to the burette

2. prepare a solution of the oxidising agent to be analysed. Add this to the conccal flask then add excess potassium iodide

3. the oxidising agent reacts with iodide ions to produce iodine which turns the solution a yellow-brown colour

4. titrate this solution with the Na2S2O3. The end point is reached when the solution becomes a straw colour. A starch indicator can be used and the end point is when all the blue-black colour disappears

what can iodine/thiosulfate titrations be used to indicate

• the ClO- content in household bleach

• the Cu2+ content in copper (ii) compounds

• the Cu content in copper alloys

the analysis of oxidising agents

what can manganese (vii) titrations be used for

the analysis for many reducing agents

• iron (ii) ions

• ethnaedioic acid