Question:
Hello,
My friends and I are doing a chemical assignment on the analysis of
household bleach. To do this, we firstly need to know how to standardize
sodium thiosulphate.
Can you please enlighten us. It would be much appreciated.
Replies:
You can find, probably several, methods for standardizing sodium
thiosulfate solutions in any introductory text on analytical chemistry.
You can also probably find methods posted on the Web.
The procedure most frequently used is based on an iodine standard.
Reagent grade iodine, available from any chemical supplier, e.g. Sigma
Aldrich, is very pure so it can be used as a primary standard. It's really
an easy method. The following is a description so you should look it up in
an analytical text for details.
Add an accurately weighed amount of iodine to a solution of excess
potassium iodide. Stir until the iodine is completely dissolved. The
solution is highly colored due to the formation of the monovalent anion (I)3. Titrate the tri-iodide solution until it is colorless.
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