Sodium Thiosulfate Solution 0.1 mol/l (0.1 N) (Catalog No. 109147)

• Reaction type:
  • Redox titration/iodometry
• Kind of titration:
  • Back-titration based on substitution
• Volumetric standard:
  • Potassium iodate
  • Potassium iodate should be preferred to the toxic potassium di chromate which is suspected to be carcinogenic.
• Method of initial introduction:
  • Division into aliquots by gravimetry

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Indication

a) visual: with starch solution 1 %; color change from blue to colorless,
b) potentiometrical:with platinum single rod measuring chain and automatic titrator.

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Analytical procedure

a) Preparation of a potassium iodate solution 1/60 mol/l (0.1 N)(Catalog No. 102404)

Approx. 3.57 g of potassium iodate (Volumetric Standard), dried for 2 h at 130 °C, are exactly weighed, transferred to a 1-l volumetric fl ask, dissolved in water GR for analysis and made up to 1 l with water. The total weight is determined to the second decimal.

Calculation of the mass fraction w (KIO3) in mg/g solution:



Cf = correction factor, calculated from the effective content of the volumetric standard acc. to the certificate divided by 100.

b) Titration:

In a titration vessel of about 300 ml, approx. 19 g of potassium iodate volumetric standard solution are analytically exactly weighed per difference weighing using a plastic syringe. 150 ml of water GR for analysis, 3 g of potassium iodide and 5 ml of hydrochloric acid 25 % are added and the iodine liberated is titrated immediately with the sodium thiosulfate solution to be tested.

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Calculation

Standard solutions which can be checked with the standardized sodium thiosulfate solution:

• Bromate solution 1/60 mol/l
• Bromide-bromate solution 0.05 mol/l
• Iodide-iodate solution 1/64 mol/l
• Iodine solution 0.05 mol/l
• Potassium dichromate solution 1/60 mol/l
• Potassium iodate solution 1/60 mol/l
• Potassium permanganate solution 0.02 mol/l (for use in iodometry