Is HClO a Strong or Weak Acid? (And Why?)

HClO (hypochlorous acid) is a weak acid. 1 It only partially dissociates in water to produce hydrogen ions (H+) and hypochlorite ions (ClO-). Unlike strong acids, HClO’s dissociation is limited, resulting in a lower concentration of H+ ions in solution.

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Key Takeaways: Is HClO a Strong or Weak Acid?

  • HClO (hypochlorous acid) is a weak acid due to its incomplete dissociation in water, leading to a lower concentration of hydrogen ions (H+) compared to strong acids.
  • The dissociation of HClO results in a solution that is less acidic and closer to neutral pH, whereas strong acids like HCl produce highly acidic solutions with a lower pH value.
  • Despite being a weak acid, HClO finds numerous applications, such as water disinfection, wound and skin disinfection, surface sanitization, dental applications, and food industry sanitization, owing to its effective oxidizing and disinfecting properties.

Why is HClO a weak acid?

HClO, also known as hypochlorous acid, is considered a weak acid due to its incomplete dissociation in water. 

When dissolved in water, it partially ionizes into hydrogen ions (H+) and hypochlorite ions (ClO-):

HClO (aq) ⇌ H+ (aq) + ClO- (aq)

In a weak acid, this dissociation process is incomplete, meaning only a small fraction of HClO molecules actually dissociates into ions. As a result, the concentration of hydrogen ions produced in the solution is relatively low compared to strong acids.

On the other hand, strong acids like hydrochloric acid (HCl) readily dissociate completely into hydrogen ions and chloride ions (Cl-) when dissolved in water:

HCl (aq) → H+ (aq) + Cl- (aq)

The strength of an acid is determined by its ability to donate protons (H+) to a solution. Strong acids have a strong tendency to donate protons, resulting in a higher concentration of H+ ions in the solution, leading to a more acidic solution. 2

Weak acids, like HClO, have a weaker tendency to donate protons, resulting in a lower concentration of H+ ions and a less acidic solution.

It’s worth noting that the strength of an acid is not solely determined by the strength of the chemical bond between the hydrogen and the acid’s conjugate base (in this case, hypochlorite ion, ClO-).

It also depends on various other factors, such as the size and electronegativity of the atoms involved and the stability of the resulting ions after dissociation. In the case of HClO, the combination of these factors leads to its classification as a weak acid.

How does the dissociation of HClO differ from that of a strong acid?

Here is a comparison of the dissociation of HClO (hypochlorous acid) with a strong acid, HCl (hydrochloric acid).

Aspect of DissociationHClO (Hypochlorous Acid)HCl (Hydrochloric Acid)
Dissociation ReactionHClO (aq) ⇌ H+ (aq) + ClO- (aq)HCl (aq) → H+ (aq) + Cl- (aq)
Degree of DissociationPartial dissociation, incomplete ionization 3 4Complete dissociation, full ionization 5
Concentration of H+ IonsLow concentration of H+ ions in solutionHigh concentration of H+ ions in solution 6
pH of SolutionLess acidic, closer to neutral pH 7Highly acidic, lower pH value 8
ConductivityLower electrical conductivity in solutionHigher electrical conductivity in solution 9
StrengthWeak acidStrong acid
Reaction with MetalsLess reactive with metalsMore reactive with metals
Reaction with BasesLess reactive with basesMore reactive with bases
Stability of Conjugate BaseRelatively stable conjugate base (ClO-)Highly stable conjugate base (Cl-)

In summary, HClO undergoes partial dissociation and results in a low concentration of hydrogen ions (H+) in the solution, leading to a solution that is weakly acidic. 

On the other hand, HCl is a strong acid that undergoes complete dissociation, resulting in a high concentration of hydrogen ions and a highly acidic solution. The differences in the degree of dissociation and the resulting concentration of H+ ions account for the contrasting properties of weak and strong acids.

Applications of HClO based on its weak acidic nature

HClO (hypochlorous acid) and its related compounds have several applications based on their weak acidic nature and oxidizing properties. Here are some of the notable applications:

  1. Water Disinfection: HClO is a powerful and selective oxidizing agent. 10 It is used as a disinfectant in various water treatment processes, including municipal water treatment, swimming pools, and water purification systems. 11 It effectively kills bacteria, viruses, and other microorganisms, making water safe for human consumption and recreational use. 12 13
  2. Wound and Skin Disinfection: Hypochlorous acid is used in medical settings for wound cleaning and disinfection. 14 It is gentle on the skin and mucous membranes but still effective against bacteria and pathogens, making it suitable for wound care and antiseptic solutions.
  3. Surface Sanitization: HClO based solutions are employed for surface disinfection and sanitization in healthcare facilities, 15 food processing plants, and public spaces. Its weak acidic nature allows for safe use on a wide range of surfaces without causing corrosion or damage.
  4. Veterinary and Animal Health: HClO is used in veterinary medicine for wound care, disinfection of surgical instruments, and general animal hygiene. 16 It can be applied safely to various animals due to its non-toxic nature at appropriate concentrations.
  5. Dental Applications: Hypochlorous acid-based solutions are used in dentistry for oral hygiene and disinfection. 17 They are used for mouthwash, irrigation during dental procedures, and treatment of gum diseases.
  6. Endodontics: In root canal treatment, hypochlorous acid is used as an irrigant to disinfect and clean the root canal system effectively. 18

Further reading

Is Ba(OH)2 a Strong or Weak Base?
Is KOH (Potassium Hydroxide) a Strong or Weak Base?
Is NH3 (Ammonia) a Strong Base or Weak Base?
Is NaOH (Sodium Hydroxide) a Strong or Weak Base?
Is Calcium Hydroxide [Ca(OH)2] a Strong Base?

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  2. pH Scale: Acids, bases, pH and buffers (article) | Khan Academy. (n.d.). Khan Academy.
  3. Weak acid-base equilibria (article) | Khan Academy. (n.d.). Khan Academy.
  6. 2. Strong and Weak Acids. (2013, October 3). Chemistry LibreTexts.
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  10. P. (n.d.). Hypochlorous Acid. Hypochlorous Acid | HClO | CID 24341 – PubChem.
  12. Block, M. S., & Rowan, B. G. (2020, June 25). Hypochlorous Acid: A Review. PubMed Central (PMC).
  14. Wang, L., Bassiri, M., Najafi, R., Najafi, K., Yang, J., Khosrovi, B., Hwong, W., Barati, E., Belisle, B., Celeri, C., & Robson, M. (2007, April 11). Hypochlorous Acid as a Potential Wound Care Agent: Part I. Stabilized Hypochlorous Acid: A Component of the Inorganic Armamentarium of Innate Immunity. PubMed Central (PMC).
  15. Block, M. S., & Rowan, B. G. (2020, September). Hypochlorous Acid: A Review. Journal of Oral and Maxillofacial Surgery, 78(9), 1461–1466.
  16. Ramey, D. W., & Kinde, H. (2015, February). Commercial and Homemade Extremely Dilute Hypochlorous Acid Solutions Are Bactericidal Against Staphylococcus aureus and Escherichia coli In Vitro. Journal of Equine Veterinary Science, 35(2), 161–164.
  17. Tazawa, K., Jadhav, R., Azuma, M. M., Fenno, J. C., McDonald, N. J., & Sasaki, H. (2023, February 18). Hypochlorous acid inactivates oral pathogens and a SARS-CoV-2-surrogate. BMC Oral Health, 23(1).
  18. Garcia, F., Murray, P. E., Garcia-Godoy, F., & Namerow, K. N. (2010, August). Effect of aquatine endodontic cleanser on smear layer removal in the root canals of ex vivo human teeth. Journal of Applied Oral Science, 18(4), 403–408.

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