Volumetric Analysis

Question 1

What is a back titration?

Answer 1

Method where an excess of a reagent is reacted with a sample. The unreacted reagent is then determined by titration.

Question 2

What is the practical method for a sodium thiosulfate solution?

Answer 2

1. Rinse a pipette with potassium iodate (V) solution and using a pipette filler, pipette 25.0 cm^3 of standard potassium iodate (V) solution into a conical flask.
2. Add approximately 1.5g of potassium iodide (excess) and of sulfuric acid (by measuring cylinder)
3. Rinse the bursted with the standard sodium thiosulfate, and then fill the burette with sodium thiosulfate, making sure the tap is filled.
4. Add standard sodium thiosulfate solution from the burette until the solution is straw/yellow in colour and add 3 drops of starch indicator solution.
5. Titrate until the indicator changes colour blue-black to colourless at the end point.
6. Repeat until results are concordant.