What factors influence the decomposition rate of sodium hypochlorite (bleach)?

Sodium hypochlorite decomposition rate is dependent on the total ionic strength of the product, temperature of the solution, pH, and heavy metal content of the solution.

The primary pathway is 3NaOCl = 2NaCl + NaClO3

The minor pathway is 2NaOCl = 2NaCl + O2

What is the ideal pH of the solution?

The ideal pH of the solution should be from 11.86-13 pH or approximately 0.25% to 0.35% excess caustic (NaOH).

What is the decomposition rate of sodium hypochlorite?

Sodium hypochlorite has a second order decomposition rate. Without salt, 200 gpl available chlorine sodium hypochlorite will decompose 4 times faster than 100 gpl product when stored at the same temperature. With the normal amount of salt produced during the reaction, (Cl2 + 2NaOH = NaOCl + NaCl + H2O), the decomposition rate is a factor of 5 greater for the 200 gpl product versus the 100 gpl product at the same temperature.

What is the decomposition rate of sodium hypochlorite with respect to changes in temperatures?

For a 10°C increase in temperature, sodium hypochlorite at the same starting strength will decompose 3.5 times faster.

What is the effect of heavy metals such as copper and nickel on sodium hypochlorite?

Decomposition of sodium hypochlorite is increased with heavy metals such as nickel and copper in solution. There is not an easy calculation method for different levels of heavy metals except for a Powell program that is not available on the website. Typical metals for nickel and copper are in the range of 50 ppb or less when sub-micron filtration is provided but many times, levels in the range of 300-400 ppb for nickel and 50-60 ppm for copper can be in the product which will create O2 and increased decomposition.

Where may I find additional information on sodium hypochlorite?

More information can be found in Powell's Sodium Hypochlorite General Information Handbook

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