Laboratory work 10 Determination of hydrogen iodide with hydrogen peroxide by the rate of constant of oxidation reaction, the order and determination of the half-life. Task: determine the reaction rate constant

Laboratory work 10
Determination of hydrogen iodide with hydrogen peroxide by the rate of constant of oxidation reaction, the order and determination of the half-life.
Task: determine the reaction rate constant:
2HJ + H₂O₂ = J₂ + 2H₂O
Equipment and reagents : 200 conical flask, burette 25 ml, 0,4% NaJ, 1 mole/l H₂SO₄, 0,025 mole/l Na₂S₂O₃, 0,5% starch solution.
Theoretical explanation. The following processes occur:
2NaJ + H₂SO₄ = Na₂SO₄ + 2HJ (a)
2HJ + H₂O₂ = J₂ + 2H₂O (b)
J₂ + 2Na₂S₂O₃ = 2NaJ + 2Na₂S₄O₆ (c)
The rate of this reaction depends on the concentration of hydrogen peroxide. The change in its concentration is determined by the equivalent amount of released iodine, which is titrated with a solution of sodium thiosulfate. Reactions (a) and (c) proceed instantly, so the speed of the total process is determined by the rate of a slower reaction (b).
Since sodium iodide is regenerated during the titration of iodine with sodium thiosulfate, the concentration of Na and HJ are practically constant and, therefore, reaction rate (b) is determined only by the concentration of H₂O₂.
The oxidation of iodic acid with hydrogen peroxide proceeds according to the kinetic equation of the first order reaction.
The kinetic equation of the first order reaction:

Work performance: 25 ml of a solution of 0.4% NaJ solution and 2.5 ml of a H₂SO₄ solution with a concentration of 1 mol/L are poured into a 200 ml conical flask.
A burette with a capacity of 25 ml is filled with a solution of Na₂S₃O₃ with a concentration of 0.025 mol/L.
Add 1 ml of Na₂S₃O₃ solution and 5 drops of 0.5% starch solution to the flask with the solution from the burette. Then 5 ml of a H₂O₂ solution are added and the mixture is stirred. When blue staining appears, turn on the stopwatch and mark the time. This is considered the beginning of the reaction (t_o). 0.5 ml of Na₂S₃O₃ are quickly added from the burette, the solution is stirred. The color of the solution disappears. After some time, a blue color appears again and the stopwatch is recorded (t1). Without turning off the stopwatch, the operation of adding a 0.5 ml Na₂S₃O₃ solution is repeated 5 more times and each time the stopwatch is recorded.

№	Volume of Na2S3O3 which is added at this moment, ml	Volume of Na2S3O3 which is added at this moment of stain, ml	The time of every stain, t in sec	k с^-1

The data obtained are entered into the table and the reaction constant for each time is calculated according to the above formula. The average value of the rate constant is calculated.

The half-life of the reaction is calculated from:
= lg2