Question

The thiosulfate titrant must be standardized. What does this mean and how is it accomplished?

Answer 1

initially thiosulfate solution concentration is measured.

but after some time if we check the concentration , then it is not as initial concentration. it changes because   thiosulfate is hygroscopic nature. that means it absorbs water from the atmosphere. so the volume of solution increses so concentration decreases. (molarity =moles /volume)

so in order to measure exact concentration of thiosulfate we need to standardized with some other solution.