Iodine- Thiosulfate Titrations

Question 1

What are the oxidised and reduced species in the iodine thiosulfate titration?

Answer 1

Oxidised: S2O32-
Reduced : I2

Question 2

What are iodine thiosulfate titrations useful for?

Answer 2

Determine:
- ClO- conc in household bleach
- Cu2+ conc in copper (ll) compounds
- Cu content in copper alloys

Question 3

Describe the procedure for the iodine thiosulfate titration.

Answer 3

1. Standard solution of sodium thiosulfate is added to the burette
2. Prepare a solution of the oxidising agent and use a pipette to add this to a conical flask and add an excess of potassium iodide which allows iodine to be produced, turning the solution a yellow-brown colour
3. Add starch indicator to the conical flask so that as the titration is carried out, the end point can be identified when the blue-black colour fades and completely disappears as all of the iodine has been reacted.

Question 4

Why is the starch indicator added close to the endpoint?

Answer 4

To prevent the starch-iodine complex from precipitating out of the solution

Question 5

What is the ratio of moles of ClO- to moles of thiosulfate?

Answer 5

1:2

Question 6

What is the ratio of moles of Cu2+ to moles of thiosulfate?

Answer 6

1:1