PUREGIA Purity Calculator 

Relationship Between Active HOCl and pH

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Chart 1 illustrates the proportion of active hypochlorous acid (HOCl) present in water across a pH range of 4.8 to 8.5, calculated using the Henderson–Hasselbalch equation (pKa = 7.53).

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At approximately pH 6.5, the solution maintains about 91.5% active HOCl, which is the highly effective antimicrobial form capable of rapidly inactivating bacteria and viruses, including COVID-19.

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However, once the pH rises above 6.5, the percentage of active HOCl begins to decrease rapidly.

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For example, if an HOCl solution has a measured pH of 7.5, the composition of the solution is approximately:

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• ~50% Hypochlorous Acid (HOCl)

• ~50% Hypochlorite Ion (ClO⁻)

 

The hypochlorite ion (ClO⁻) is the chemical species commonly associated with sodium hypochlorite (NaClO)solutions, widely known as household bleach.

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Furthermore, under conditions where the pH exceeds 6.5, HOCl molecules become less stable and tend to dissociate more rapidly after production.

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For this reason, proper pH control is an important factor in maintaining a high level of active HOCl in disinfecting solutions.

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