I. 4.2 Selection of sulfuric acid solution dosage

The reaction between S2O32- and I2 was rapid, complete, but the iodimetric titration was performed under pH 8, neutral, and slightly acidic conditions.

Under alkaline conditions, S2O32- reacts with I2 as follows.

This complicates the reaction.

Decomposition of NA2S2O3 solution in a strongly acidic solution:

In addition, I I is easily oxidized by 0 in the air in acidic solution:

This reaction proceeds very slowly in neutral solution, but accelerates with increasing H - 1 concentration in solution.

If exposed to direct sunlight.

The reaction rate is accelerated.

Therefore, iodimetry is generally carried out in neutral or weak acidic solution and at low temperature.

To reduce I I's contact with air, titrations should not be violently oscillated.

Based on the above analysis.

Different amount of sulfuric acid solution was added for comparison experiment.

I. 6 Repetitive experiments

Repeated experiments were performed on the same sample.

3 conclusion

The optimum operating conditions for the determination of effective chlorine in sodium hypochlorite by iodimetry were determined by a large number of experiments and the comparison of various operating conditions.

It is proved that the operating conditions for the determination of available chlorine by iodimetry in GB/T10666-1989 are also applicable to calcium hypochlorite products by sodium method with different processes and raw materials, thus unifying the determination methods of available chlorine for sodium method and calcium method products.

At the same time, it can be seen from the above experiments that the iodine quantity method is used to determine the effective chlorine content in sodium calcium hypochlorite products, with high accuracy, precision and good repeatability.

This method is feasible.