Question

Standardization of sodium thiosulphate against potassium bromate

Answer 1

1. Potassium bromate, 0.015 M. Transfer about 1.5 g of reagent-grade potassium

bromate to a weighing bottle, and dry at 110°C for at least 1 hr. Cool in a desiccator. Weigh approximately 1.3 g (to the nearest 0.1 mg) into a 500-mL volumetric flask; use a powder funnel to ensure quantitative transfer of the solid.

Rinse the funnel well, and dissolve the KBrO3 in about 200 mL of distilled

water. Dilute to the mark, and mix thoroughly.

Solid potassium bromate can cause a fire if it comes into contact with damp

organic material (such as paper towels in a waste container). Consult with the

instructor concerning the disposal of any excess.

2. Sodium thiosulfate, 0.05 M. Follow the directions in Section 37G-1; use about

12.5 g of Na2S2O3 5H2O per liter of solution.

3. Starch indicator. See Section 37G-1(b)