Hypoiodous Acid

Hypoiodous Acid: An Introduction

A hypoiodous acid is an inorganic compound having a molecular formula of HOI. It occurs when an iodine solution reacts with mercury or silver salts. The removal of protons results in the formation of hypoiodite. 

However, hypoiodite is an inorganic compound present in the form of monovalent an-ion. Mainly, it gets obtained through dehydronation (removal of a proton) of the acidic compound HOI. It exists in the forms of an iodine oxide, a monovalent inorganic an-ion and an iodine oxoanion.

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Synthesis of Hypoiodous Acid Oxyacid

The acid HOI is highly unstable and weak compared to other acids. Mostly, one can obtain it via the treatment of mercury oxide with iodine in an aqueous solution. Besides, it can also form unstable salts in a solution when iodine reacts with an alkali.

It is a part of an iodine species that has a volatile nature. It forms a greenish-yellow liquid that is highly unstable in the state. Mostly, it occurs as an inorganic complex dissolving quickly in most aqueous solutions.

Therefore, the disassociation of this acidic chemical compound becomes easy in water. It releases elements related to an iodine group on decomposition. The synthesis process of this acid also involves the iodine component.

The synthesis of this acid HOI occurs when iodine interacts with cold and dilute solution of sodium hydroxide. It, in turn, results in sodium hypoiodite which then hydrolyses to form the acidic compound HOI.

The equation below shows how it occurs. 

2NaOH + I2 → NaIO + NaI + H2        …… (1)

In the above equation, interactions take place between sodium hydroxide and iodine, respectively. Its reaction results in the formation of sodium hypoiodite, sodium iodide and water. Sodium iodide is a water-soluble compound in the ionic state.

The second equation depicts the further break down of the components gathered.

NaIO + H2O → NaOH + HOI …… (2)

The interaction between sodium hypoiodite and iodine forms sodium hydroxide and HOI. It can be understood from above.

Another possible way of generation of the HOI occurs when iodine dissolves in water and the acid form through hydrolysis.

The following equations depict the formation of iodine and the acid HOI. Try going through it carefully to understand how it takes place.

I2 + H2O HIO + I- + H+

In the above equation, iodine dissolves in water to generate HIO and iodide. However, interactions between HIO atoms or molecules can result in iodous acid and iodate. However, one can also generate HIO from iodous acid (HIO2).

The below equation depicts it. Go through it to understand it to clear your concepts.

2 HIO → HIO2 + I- + H+

HIO2 + HIO → IO-3 + I- + 2 H+            and ….. (1)

2 HIO2 → IO-3 + HIO + H+                   ..... (2)

Similarly, the acidic component HIO also dissolves in water to form hypoiodite. The following equation shows it.

  HIO → IO- + H+

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Figure 1: The above illustration shows the chemical or molecular structure of HOI.

Did you know: Hio4 acid name is another name of periodic or metaperiodic acid. It is an iodine oxoacid arising as a conjugate acidic substance from a periodate.

Properties of this Acid

  • The IUPAC name of the HOI is Hypoiodous acid.

  • The chemical compound appears in the form of a greenish-yellow solution.

  • It does not have any particular odour, and it quickly dissolves in water or aqueous solutions.

  • The hypoiodous acid formula is HOI, and its conjugate base is known as hypoiodite.

  • The molecular weight or mass of the acid is 143.912 g/mol.

  • The number of heavy atoms of the acid amounts to 2, whereas the number of isotope atoms amounts to 0.

  • The complexity of this chemical compound HOI amounts to 2.

  • The exact mass has the property value amounting to 143.90721 g/mol, which is similar to its monoisotopic mass.

  • The topological polar surface area of this acid has the property value accounting to 20.2 Ų.

  • The number of hydrogen bond donor amounts to 1, identical to the number of hydrogen bond acceptors.

  • Besides, the number of covalently-bonded unit of this acid amounts to 1.

  • The XLogP3-AA has the property value of 0.4 for this chemical compound.

  • The compound HOI contains a density amounting to 3.207 gram per cubic centimetres (g/cm3).

Did You Know: Hio2 acid is the other name of a chemical compound iodous acid which is iodine oxoacid. It forms a conjugate acid resulting from an iodite.


The acid HOI has multiple applications due to its reactive state and other facilitating properties. Read the below pointers carefully to learn more about its uses to ace your studies.

These are as follows: 

  1. Due to the reactive nature of this chemical HOI, it gets used in the treatment of drinking water. It is a crucial component that gets applied in iodine for the oxidative cure of water.

  2. The chemical compound HOI gets used as a powerful oxidising agent. Therefore, the acid finds its applications in rocket fuels and also in insulation in many industrial sectors.

  3. It also gets used in the prevention, control and reduction of pests in the agricultural sector. Use of the complex protects the crops and plants against harmful pests destroying them.

  4. The compound also finds its applications in the field of atmospheric samplers. It helps in studying and elaborating the abnormal increasing rate of organic fractions.

  5. The acid also gets applied to remove chloramines from water in a swimming pool apart from reducing eye irritations.

  6. The chemical also gets applied as vital agents in the removal of microbial or fungal growth. Besides, the key compounds of iodine get applied for sanitisation purposes.

  7. Moreover, the acidic chemical HOI also gets used as an origin for the formation of OH radicals.

Rack Your Brains

Here are a set of questions related to the chemical HOI or hypoiodous acid. Try solving them to check your preparation.

1. What Happens When Iodine Gets Oxidised by Ozone in a Moist Surrounding?

  1. Hypoiodous acid formation

  2. Iodic acid

  3. Formation of periodic acid

  4. Hydroiodic acid forms

  5. None of these

2. What is the pKa Level of an HOI?

  1. 10.5 in water

  2. 8.00 

  3. 9.18

  4. 7

3. Which of the Following the Acidic HOI Component Realises after Disproportioning? 

  1. Iodides 

  2. Iodates

  3. Sodium chloride

  4. Both option ‘a’ and ‘b’.

  5. None of the above

4. Oxidoiodine is Another Name of Which of the Following Compound?

  1. HOI 

  2. H2SO4

  3. HCl

  4. HNO3

Hypoiodous Acid Important Points

  • In simple words, the acid HOI is iodine’s oxyacid, resulting when iodine breaks down completely in water, or higher oxyacids reduce.

  • The other names of this chemical compound HOI are hypoiodite.

  • The acid gets used in agricultural areas for controlling and destructing pests. 

  • It exists as a conjugate acid appearing from a hypoiodite.

  • Hypoiodite is an ion having a conjugate base of the acidic compound HOI. The chemical or molecular formula of a hypoiodite is IO-.

  • The nature of this acidic chemical complex HOI is weaker than other acids.

  • The chemical compound hypoiodous acid decomposition results in the formation of iodides and iodates.

  • The acid gets used as a powerful agent for oxidisation purposes.

  • The chemical compound HOI is odourless.

  • The acid HOI is highly soluble in water and other aqueous solutions.

  • Moreover, the complex is comparatively weaker than other acids because it has a pKa of 10.5 approx.

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FAQ (Frequently Asked Questions)

1. What is the Other Name of HOI?

Ans. The other name of the chemical component HOI is hypoiodous acid. It is a weak acid which forms when iodine’s aqueous solution gets treated with silver salts or mercury.

2. What Type of Acid is Hypoiodite?

Ans. The hypoiodous acid is a weak type of acid since it has a pKa of around 10.5. Its conjugate base is (IO-). It is an inorganic compound occurring at a highly unstable state. It is comparatively weaker than other acids, such as sulphuric or nitric acid.

3. Where is the Chemical Compound HOI Primarily Used?

Ans. The primary function of a hypoiodite is prevention and control of pests. It increases the chances of plant growth in turn. Further, the chemical compound finds its uses in rocket fuels and an insulator.

4. How Does a Hypoiodite Reagent Get Prepared?

Ans. A hypoiodite is a highly unstable ion that breaks down quickly to iodide and iodate. A reagent can get prepared when iodine reacts with any base agent. The chemical or molecular formula of a hypoiodite is IO-.