Oxoacids of Halogen- Definition, Types of Oxyacids, Properties, Structures, Uses, Practice Problems, FAQs

Have you seen white power spread near water tanks of hospitals, schools and most public places? Have you asked your teachers what is that white powder? That is the active ingredient calcium oxychloride is used to destroy germs and bacteria in drinking water. Halogens have always been an important ingredient for any chemical synthesis. Bleach (calcium hypochlorite) is also used in washing clothes in laundries also. There are wide applications of oxyacids of halogen which we will study on this page.

Oxoacids have a large application in chemical synthesis and are used with precautions. 

Let’s study these acids in detail!

Table of content:

• What are oxyacids?
• Types of oxyacids
• Oxoacids of Fluorine
• Oxoacids of Chlorine.
• Oxoacids of Bromine
• Oxoacids of Iodine

What are oxoacids?

From top to bottom, Group 17 elements include fluorine, chlorine, bromine, iodine, and astatine. They're called halogens because they produce salt. The members of this group have a lot in common. Physical and chemical characteristics are arranged in a predictable way. Each of these elements has seven electrons in its valence shell ns² and np⁵ is their electronic setup.

The suffixes –ous and –ic are used again to represent the lower and higher amount of oxygens in the acid formula if the acid contains oxygen (referred to as an oxoacid). Hydrogen, oxygen, and other components make up oxyacids. Oxyacids are acids that contain hydrogen, oxygen, plus another element.

Types of Oxoacids:

Halogens combine with oxygen to form oxoacids of halogens. We will study oxoacids compounds formed by halogen in detail. Here are the listed oxoacids formed by halogens.

Oxoacids of Fluorine:

• Fluorine forms only one oxoacid, HOF, known as fluoric (I) acid or hypofluorous acid, due to its high electronegativity and tiny size.
• HOF is an inflammable, colourless gas. It was created utilising the matrix isolation technique for the first time in 1968. F₂ and H₂O were confined in a solid nitrogen matrix that was non-reactive.
• The gases were photolyzed, resulting in the formation of the HOF . Because it was also locked in solid nitrogen, it couldn't collide or react with other molecules like H₂O or O₂. As a result, a product was created. F₂ has recently been made into HOF by running it through an ice bath at 0℃ and removing the product into a cold trap. 
• F was assumed to be incapable of forming oxy acids for a long time. It is already well recognised that HOF can be prepared in a variety of ways.

F₂(g)+H₂O(aq) ⇌ HOF(aq)+HF(aq)

• HOF is a volatile compound that decomposes into HF and O₂ on its own. 

• It's a powerful oxidizer that can quickly convert H₂O to H₂O₂. The -OF group is found in oxidising agents like F₃C-OF, O₂N-OF , F₂S-OF, F₅S-OF and O₃Cl-OF 

Structure of HOF:

Oxoacids of Chlorine:

Chlorine forms maximum oxoacids among halogens. Let’s study them in detail.

1. Hypochlorous Acid, HClO: This acid only exists under solution. It's made by mixing precipitated HgO with chlorinated water and stirring it.

Preparation of HClO:

It's made commercially by passing CO2 through a suspension of bleaching powder and then distillings it.


Properties and reactions of HClO:

• It's a very weak acid. The concentrated solution is yellow in colour but upon dilution, the solution slowly becomes colourless. It decomposes and is unstable
  
• With the release of hydrogen, it dissolves magnesium.
  
  It forms hypochlorites when alkalies are present.
• It has a strong oxidising and bleaching effect. This is owing to the easy release of nascent oxygen.
  

Structure of HClO: This is the structural representation of HClO

2. Chlorous Acid, HClO₂:
Chlorous acid has the formula HClO₂ and is an inorganic chemical. It's a very weak acid. In this acid, chlorine has an oxidation state of +3. Although it is a weak acid, it is more powerful than HClO.

Preparation of HClO₂:
When barium chlorite suspension in water is treated with H₂SO₄, it is produced in aqueous solutions. The insoluble barium sulphate is removed using filtration.

 Properties and reactions of HClO₂:

• The solution is colourless when it is first made, but it quickly decomposes to ClO2, which turns the solution yellow.
  
• Auto-oxidation occurs in this acid.
  
• Iodine is liberated from KI using this acid.
  

Structure of Chlorous Acid:

• Chloric acid , HClO₃:
  Chloric acid is a clear liquid with no colour. It will hasten the combustion of combustible materials and can ignite the majority of them on contact. It corrodes both metals and tissue. It's used to create other chemicals and as a reagent in chemical analysis.
   

Preparation of HClO₃:
This acid only exists under solution. Dilute H₂SO₄ reacts with barium chlorate to produce this acid. Barium sulphate which is formed in the reaction is precipitated out.

Properties and reactions of HClO₃:

• Concentrated chloric acid is a colourless liquid with a strong odour.
• It decomposes in the presence of light. It is, nevertheless, stable in the dark. In the presence of light, it functions as a potent oxidising and bleaching agent. When organic materials like paper, cotton, and wool come into touch with the acid, they catch fire.
• If attempts are made to evaporate HOBrO₂ to dryness, they will detonate. The most important is:
  
• There are two techniques to make chlorates:

(I) Putting Cl₂ into a hot NaOH solution 
(II) Hot chloride is electrolyzed and aggressively agitated.
Only one-sixth of the chlorine gets transformed to ClO₃^-, indicating that the process is inefficient. The NaCl produced, on the other hand, is electrolyzed again and hence does not go to waste.

Structure of chloric acid:

Oxoacids of Bromine:

1. Hypobromous acid:
HOBr is a known hypohalous acid of bromine, having +1 oxidation state of Br. HOBr is very unstable and exists only in an aqueous solution. Although this is a weak acid, but is an effective oxidising agent in acidic solutions.
This acid only exists under solution. It's made by mixing precipitated HgO with brominated water and stirring it.
Preparation of HOBr:

Only at temperatures around 0°C hypobromites (OBr^-) may be formed; at temperatures above 50°C, quantifiable yields of BrO₃^- are obtained

Properties of HOBr:

• HOBr i.e also known as hypobromous acid has a molecular mass equal to 96.921 amu.
• Density of this acid comes out to be 2.470 g cm^-3.
• HOBr is volatile in nature having boiling point around 20℃-25℃
   

Structure of HOBr:

• Bromic acid HBrO₃:
  Bromic acid is also known as Hydrogen bromate acid or Bromic (V) acid.
  
  Preparation of HBrO₃:
  This acid only exists under solution. Dilute H₂SO₄ reacts with barium bromate to produce this acid. Barium sulphate which is formed in the reaction is precipitated out.
  
  Properties and reactions of HBrO₃:

• It's a clear, colourless solution. The colour of the solution changes yellow as it decomposes to bromine at room temperature. 
• Bromic Acid's molecular or chemical formula is also written as HBrO₃.
•  HOBrO₂ has a molecular mass equal to 128.91 u.
  If attempts are made to evaporate HOBrO₂ to dryness, they will detonate. The most important reaction is
• This acts as a good oxidising agent and is a typical constituent in the Belousov-Zhabotinsky reaction.

Structure of HBrO₃:

• Perbromic acid HBrO₄:
  Perbromates were not discovered until 1968. They are uncommon in nature. Preparations of Perbromic acid are very complex which is very uncommon.

Properties and reactions of HBrO4:

• Perbromates could not exist for a long time until traces were recovered from of SeO₄^2- . They can be generated from bromates by the action of powerful oxidising agents F₂ and XeF₂ or by electrolysis of an aqueous solution.
  
  The yield of the above reaction is close to 20%

The yield of the above reaction is close to 10%

• Perbromates that are solid are stable. KBrO₄ is isomorphous with KClO₄ and stable up to 275°C. The concentrated acid, HBrO₄, is stable in solution up to a concentration of 6 M, but it is a strong oxidizer. Perbromates oxidise slowly in dilute solutions.

Structure of HBrO₄:

Oxoacids of Iodine:

• Hypoiodous acid:
  HOI is a known hypohalous acid of iodine, having a +1 oxidation state of I.
  
  Preparation of Hypoiodous acid:
  1. This acid only exists under solution. It's made by mixing precipitated HgO with brominated water and stirring it.
  
  2. Iodine interacts with a cold, weak sodium hydroxide solution to make sodium hypoiodite, which is then hydrolyzed to produce hypoiodous acid.
  
  Properties and reactions of HOI:

• Hypoiodous acid has the chemical formula HOI and is a greenish-yellow solution.
• Hypoiodous Acid is a volatile iodine species found in steam/air atmospheres that is neither elemental nor organic.
• At all temperatures, hypoiodites disproportionately quickly, and IO₃^- is quantitatively created.
  

Structure of HOI: 

• Iodic acid:
  HIO₃ or iodic acid, is a white solid that is relatively stable.
  Preparation of Iodic acid:
  This is a two-stage preparation of iodic acid.

• 
  
• Iodic acid is made by oxidising iodine I₂ with powerful oxidants such nitric acid HNO₃, chlorine Cl2 or chloric acid HClO₃ . One of these reactions is represented as:
  

Properties and reactions of Iodic acid:

• With a pKa of 0.75, iodic acid is a relatively strong acid.
• In acidic solutions, it is highly oxidising; in basic solutions, it shows less oxidising behaviour.
• When iodic acid is used as an oxidant, the process produces either iodine or the iodide ion.
• Because it was known that iodic acid is reduced by hydrochloric acid when a solution containing the two chemicals is evaporated, the presence of hydrochloric acid in the iodic acid solution seemed likely to preclude the development of a quantitative approach.
  

Structure of Iodic acid:

• Periodic acid:
  Iodine's highest oxoacid is periodic acid, in which the iodine is in an oxidation state +7. It can be found in two forms, like all periodates: orthoperiodic acid (H₅IO₆) and metaperiodic acid (HIO₄).

Preparation of Periodic acid:The oxidation of a sodium iodate solution under alkaline conditions, either electrochemically on an PbO₂ anode or by chlorine treatment, is used in modern industrial-scale production.

HIO₄.2H₂O or H₅IO₆ is the most prevalent form of periodic acid. This is referred to as paraperiodic acid.

Properties and reactions of Periodic acid:

• Periodic acid is a crystalline, colourless substance. Iodine is seen in oxidation state +7. Periodic Acid is the highest oxoacid of iodine here.
• Periodic acid occurs as white crystals that melt at 128.5 °C due to decomposition. When heated to 100 °C under reduced pressure, water is lost, resulting in periodic acid HIO₄ This ultimately decomposes under high heat, losing O₂ and producing I₂O₅.
  
• Periodic acid are employed in the oxidation of organic molecules. Mn²⁺will be oxidised to MnO₄^- using this periodic acid.

Structure of Periodic acid:

Practice Problems:

Q1. ClO₃^- is shaped like a ____________.
A. tetrahedron
B. pyramid
C. octahedron
D. pentagon
Answer: B
Solution: ClO₃^- ion exhibits pyramidal geometry, according to VSEPR theory, due to the presence of 1 lone pair and 3 bond pairs, resulting in sp³ hybridization.

Q2.HClO4 ionises faster than HClO because of ___________
A. low ionisation energy of O-H bond in HClO than that of HClO₄
B. high ionisation energy of ClO^- than that of ClO_4-
C. high ionisation energy of O^-H bond in HClO than that of HClO₄
D. low hydration energy of ClO^- than that of ClO₄^-
Answer: C
Solution: Due to resonance stabilization of ClO₄^-, the anion is highly stabilized resulting in an easier breakage of the O-H bond. As a result, perchloric acid (HClO₄), acts as a stronger acid in comparison to hypochlorous acid (HClO).

Q3. Which among the following requires the least energy to break the O-H bond present in oxoacids of chlorine?
A. HClO
B. HClO₂
C. HClO₃
D. HClO₄
Answer: D
Solution: The acidic strength of oxo acids is linked to anion resonance stabilisation. Higher the acidity, the greater the stability of the conjugate base. It can also be phrased as “The stronger the acid, the greater the resonance stabilisation of the anion”.

ClO^- has zero resonating structures, ClO₂^- has two resonating structures, ClO₃^- has three resonating structures and ClO₄^- has four resonating structures. 

Hence, HClO₄ is the acid which has maximum acidic strength among all. 

Q4. Glycol splitting agent is also known as__________
A. HClO₄
B. HIO₄
C. HClO₃
D. HIO₃
Answer: B
Solution: Because it splits (oxidises) 1:2 glycols into aldehydes, HIO₄ is known as a glycol splitting agent.

Frequently asked questions- FAQ

Q1. What are the applications of fluorine on regular basis?
Solution: There is a variety of application which helps us on daily basis. Some of these are:
Fluorine compounds can be found in toothpaste and tap water. 

• Fluorine is an important medicine because it reacts strongly with tooth enamel and helps to prevent tooth decay.
• The bleaching procedure makes extensive use of chlorine. It's also utilised in gold and platinum metallurgy.
   

Q2. Is it safe to drink chlorinated water?
Solution: Yes. The ISO Certified Labs regulates the quantity of chlorine in drinking water to ensure that it is safe to drink. The amounts of chlorine used to disinfect drinking water are unlikely to have long-term health consequences. 250 mg L^-1is the acceptable level.


Q3. What happens if you consume a large amount of chloric acid?
Solution: Pain, trouble swallowing, nausea, and vomiting can all result from ingesting concentrated chloric acid which may be dangerous for human health.

Q4. What should the pH of hypochlorous acid be to avoid side effects?

Solution: The pH of the HOCl solution must be kept between 3.5 and 5 in order to keep it stable, maximise its antibacterial activity, and reduce unpleasant side effects.

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