Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Sodium Thiosulphate
Name:   Brianna
Status: N/A
Age:   18
Location: N/A
Country: N/A
Date: 2000

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.

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.

Vince Calder

Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory