Reactions: KBrO3 + 5 KBr + 6 HCl 6 KCl + 3 H2O + 3 Br2 C6H5OH + 3 Br2 C6H2OHBr3 + 3 HBr 3 Br2 + 6 KI — Physical Chemistry — Kinetics Chemistry Question

Reactions:
KBrO₃ + 5 KBr + 6 HCl 6 KCl + 3 H₂O + 3 Br₂
C₆H₅OH + 3 Br₂ C₆H₂OHBr₃ + 3 HBr
3 Br₂ + 6 KI 6 KBr + 3 I₂
6 Na₂S₂O₃ + 3 I₂ 3 Na₂S₂O₃ + 6 NaI

Chemicals and solutions:
Phenol, solid, 0.3 g
* KBrO₃, aqueous solution, c = 0.02 mol dm -3
* H₂SO₄, aq., c = 3 mol dm -3
KBr, solid
KI, solid
* Na₂S₂O₃, aqueous solution, c = 1 mol dm -3
Starch indicator.

Preparation of Na₂S₂O₃ aqueous solution, c = 0.1 mol dm -3
Weigh 25 g of Na₂S₂O₃ (AR grade) in a small beaker. Quantitatively transfer it to a 1 dm 3 volumetric flask. Prepare the solution using freshly boiled distilled water. Add 3 drops of chloroform while preparing the solution. Avoid exposure to light.

Standardisation of Na₂S₂O₃ solution
Weigh out accurately 0.14 to 0.15 g of dry potassium iodate. Dissolve it in 25 cm 3 of fresh, boiled distilled water and add 2 g of iodate free potassium iodide. Add 5 cm 3 of sulphuric acid solution (c = 0.5 mol dm -3). Titrate the liberated iodine with thiosulphate solution with constant shaking. When the colour of the solution is pale yellow add 200 cm 3 of distilled water and 2 cm 3 of starch indicator. Continue the titration until the colour changes from blue to colourless.

Procedure
Dissolve the given sample of phenol to 250 cm 3 with distilled water. Take 25 cm 3 of the phenol solution into 250 cm 3 stoppered conical flask. Add 25 cm 3 of standard potassium bromate solution and 0.5 g of potassium bromide. Add 5 cm 3 of aqueous solution of sulphuric acid (c = 3 mol dm -3). Stopper the flask immediately. Mix the reagents and let them stand for 15 min (avoid exposure to light). Then, add 2.5 g of potassium iodide rapidly. Re-stopper the flask immediately and swirl the contents of the flask to dissolve the solid.
Titrate the liberated iodine with standard Na₂S₂O₃ solution (c = 0.1 mol dm -3 using starch indicator.