Chromic Acid (H2CrO4) - Structure, Preparation, Properties, Uses, FAQs

Q: What are the types of chromic acid?

H 2 Cr 2 O 7 is chromic acid molecular. Molecular chromic acid has a lot in common with sulfuric acid H 2 SO 4 and chromic molecular acid. Only seven strong acids can be classified as sulfuric acid. Due to the laws of the "first order energy of ionisation" idea, the first proton is more quickly lost. It is very similar to sulfuric acid deprotonation. Since the multiple acid basis titrations (especially when the starting material is the acid and the basis is the Titrant) include more than one proton, protons can leave one acid at a time. Dichromic acid is. H 2 Cr 2 O 7 It is the fully protonated ion form, dichromate acid. Dichromic Acid. It is created by chromium trioxide being added to molecular chromic acid. When it reacts, dichromic acid is the same as aldehyde or ketone. The difference though is that only a ketone oxidises a secondary ketone and only dichromic acid oxidises aldehyde. It is probably present in chromic acid cleaning solutions with chromosulfuric acid.

Edited By Team Careers360 | Updated on Jul 02, 2025 04:54 PM IST

Chromic acid is an oxide with chemical formula H₂CrO₄. Another name of chromic acid is Tetraoxochromic acid or Chromic(VI) acid. This article covers structure ,preparation ,properties and some uses of chromic acid. Chromic acid has a +6 (or VI), often known as hexavalent chromium oxidisation state. Chromium can shows a number of oxidation state,+6 is the highest among them.

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Chromic acid formula
Structure of chromic acid
Preparation of chromic acid
Properties of chromic acid
Uses of chromic acid

Chromic acid formula

Chromic acid formula is H₂CrO₄

Structure of chromic acid

chromic acid structure is shown below.

Structure of chromic acid

Molecular chromic acid

H₂CrO₄ is the molecular chromic acid Molecular chromic acid has many common things to do with sulphuric acid, H₂SO₄ Molecular chromic acid. It is only possible to classify sulfuric acid as part of the list of 7 strong acids. The first proton is more easily lost due to the laws related to the concept of "first order ionisation energy." It is quite similar to deprotonation of sulfuric acid. As there are more than one proton in the process of versatile acid base titrations (particularly when the acid is the beginning material and the base is the titrant), protons can leave one acid at a time.

The anhydride of molecular chromic acid is chromium trioxide. It is a Lewis acid and can react in a non-aqueous media like dichloromethane with a lewis base, such pyridine (Collins reagent).

Dichromic acid

H₂Cr₂O₇ is the dichromic acid. Dichromic acid, is the completely protonated form of the dichromate ion. Dichromic acid can also get when you interact with aldehyde or ketone by adding chromium trioxide to molecular chromic acid. Dichromic acid is the same as aldehyde or ketone when it is reacting. However, the difference is that a secondary ketone is only oxidised by a ketone and dichromic acid only oxidises the aldehyde. It is likely present with mixed chromosulfuric acid in chromic acid cleaning solutions.

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Preparation of chromic acid

In chromic acid preparation a mixture formed by the addition of concentrated sulfuric acid to a dichromate is commonly referred to as chromic acid, which can contain a range of chemicals including solid chromium trioxide.

Properties of chromic acid

Molecular weight of chromic acid is 118.008 g/mol. The melting point of chromic acid is 197 °C Chromic acid has a boiling point of 250 °C .Chromic acid has a density of 1.201 g/cm³

Uses of chromic acid

Chromic acid uses are given below.

Chromic acid can be used in chromium plating in the role of an intermediate
Chromic acid is used in glasses especially in coloured glass and ceramic glass
Chromosulfuric acid and sulfochromic mixture is a strong oxidising agent for glass cleaning in the laboratory.
Chromic acid can shine raw metal and is therefore utilised in the tool repair sector.
Chromic acid was used in hair colouring in 1940.

The dichromic acid H₂Cr₂O₇ is the protonated form of the dichromate ion and can also be obtain by adding chromium trioxide to dichromic acid. It can act in the same exact way when interacting with aldehyde or ketone. The warning to this argument, is that only a ketone oxidises a secondary ketone and dichromic acid oxidises aldehyde exclusively. The aldehyde would be oxidised to a ketone for the first stage of the process and oxidised to a carboxylic acid again, subject to no significant steric obstacle to this reaction.

Chromic acid may oxidise various types of organic molecules and for this reagent a number of variants have been produced. Chromic acid is known as the Jones reagent in the aqueous sulphuric acid and acetone, which, while seldom impacting unsaturated bonds, oxidises primary and secondary alcohols, respectively, in carbonic acids and ketones.

Pyridine Chloride is produced by chromium trioxide and by pyridine chloride. This reaction transforms primary alcohols to the appropriate aldehydes (R-CHO).

Chromic acid test

In chromic acid test Jones reactant is used to oxidize aldehydes and alcohols. Jones reactant reduces chromic acid resulting in change of colour.

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Reaction

Chromic acid can oxidise various organic molecules and numerous modifications have been made in this reagent.

The Jones Reagent, which oxidises primary and secondary alcohol to carboxylic acids and ketones, while seldom damaging unsaturated bonds, is chromic acid in aqueous sulfuric acid and acetone
Chromium trioxide and pyridinium chloride are produced with pyridinium chlorochromate. This reagent transforms primary alcohols into the relevant aldehydes (R–CHO)
A chromium trioxide and pyridine adduct utilised for various oxidations.
Chromyl chloride, the chemical molecule produced from chromic acid is well-determined.

Oxidation of phenol with chromic acid

Benzoquinone is generated via oxidation of phenol with chromic acid.

Oxidation of phenol with chromic acid

Phenol oxidation with an acidified sodium dichromate solution will be achieved in the first step. The acidified solution signifies that an acid such as sulphuric acid is present. Now the reaction is further take place to produce benzoquinone, which is a conjugated diketon.

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Health problems

There are many hazardous and carcinogenic toxicities associated with hexavalent substances such as chromium trioxide, chrome acids, and chlorochromate. Therefore, only the aircraft industry and not other industry scales uses chromic acid oxidation.

Alternative reagents

Chromic acid is one of various reagents, including several catalytic in the oxidation of alcohols or aldehydes into carboxylic acids. Nickel (II) salts, for example, catalyse bleach oxidations (hypochlorite). Aldehydes are oxidised to carboxylic acids rather easily, and weak oxidants are plenty. For this reason, silver(I) compounds were utilized. Each oxidant has its own pros and cons. Electrochemical oxidation is often possible rather than employing chemical oxidants.

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Frequently Asked Questions (FAQs)

1. What are the applications of chromic acid?

This chemical is commonly used in chromium plating as an intermediate. Coloured glass and ceramic glazes are also utilising chromic acid. This chemical became part of a number of hair dyes in the 1940s.Chromic acid is a powerful oxidizing agent for glass cleaning in a laboratory is chromosulfuric acid and sulfochromic combination. Chromic acid may shine raw metal and hence is used for tool repair. Different types of organic molecules may oxidise Chromic acid, which has a number of variations. Aqua sulfuric acid and acetone are known as chromic Acid Jones, which oxidises primary and secondary alcohols, in carbonic acid and ketone, while seldom affecting unsaturated bonds. Chromium trioxide and pyridine chloride are generated from pyridine chloride. This reaction turns primary alcohols into the right aldehyde (R-CHO).

2. How do you prepare chromic acid?

First, a little water must be added with sodium dichromate or potassium dichromate for paste production. Chromic acid is generated upon application of sulfuric acid in the paste and constant mixing.

3. What neutralizers are most suited for chromic acid neutralisation?

First, a good amount of water must dilute chromic acid. After the diluting process, it can then be neutralised using a sodium/ potassium metabisulfite, sodium thiosulfate, or sodium sulfite are some very good neutralising substances.

4. What are the risks associated with chromic acid?

The reproductive harm can be caused by chromic acid. Chromic acid is a chemical corrosive, and contact with the skin can cause significant irritation, and may cause damage to the eye. Chromic acid can cause cough, wheezing, and/or shortness of breath to irritate the nose, throat and lung. The toxicity of hexavalent compounds such as chromium trioxide, chromium acids and chlorochromate is many dangerous and carcinogenic. Therefore, chromic acid oxidation is used solely by aircraft industry and not by other industries.

5. What are the types of chromic acid?

H₂Cr₂O₇ is chromic acid molecular. Molecular chromic acid has a lot in common with sulfuric acid H₂SO₄ and chromic molecular acid. Only seven strong acids can be classified as sulfuric acid. Due to the laws of the "first order energy of ionisation" idea, the first proton is more quickly lost. It is very similar to sulfuric acid deprotonation. Since the multiple acid basis titrations (especially when the starting material is the acid and the basis is the Titrant) include more than one proton, protons can leave one acid at a time.

Dichromic acid is. H₂Cr₂O₇ It is the fully protonated ion form, dichromate acid. Dichromic Acid. It is created by chromium trioxide being added to molecular chromic acid. When it reacts, dichromic acid is the same as aldehyde or ketone. The difference though is that only a ketone oxidises a secondary ketone and only dichromic acid oxidises aldehyde. It is probably present in chromic acid cleaning solutions with chromosulfuric acid.

6. How is chromic acid typically prepared in the laboratory?

Chromic acid is typically prepared by dissolving chromium trioxide (CrO3) in water or by reacting potassium dichromate (K2Cr2O7) with sulfuric acid (H2SO4). The reaction with sulfuric acid produces a mixture known as "chromic acid solution" which is more stable and commonly used in various applications.

7. What is the relationship between chromic acid and chromate compounds?

Chromic acid is the parent compound of chromate compounds. In aqueous solutions, chromic acid dissociates to form hydrogen ions (H+) and chromate ions (CrO4^2-). These chromate ions can further react with metal ions to form various chromate salts. Understanding this relationship is crucial for comprehending the chemistry of chromium in different oxidation states and its behavior in solution.

8. What is the relationship between chromic acid and dichromates?

Chromic acid and dichromates are closely related. In acidic solutions, chromic acid can condense to form dichromic acid (H2Cr2O7), which is the acid form of dichromate ions (Cr2O7^2-). Dichromates are often used as a more stable source of Cr(VI) in reactions where chromic acid is needed. The equilibrium between chromate and dichromate species in solution is pH-dependent, with dichromates favored in more acidic conditions.

9. How does the presence of other acids affect the properties of chromic acid?

The presence of other acids, particularly strong acids like sulfuric acid, can significantly affect chromic acid's properties. In the presence of sulfuric acid, for example, the equilibrium shifts towards the formation of dichromate ions (Cr2O7^2-), enhancing the oxidizing power of the solution. This mixture, known as chromic acid solution or Jones reagent, is more stable and more commonly used in laboratory and industrial applications than pure chromic acid.

10. What is the Jones oxidation, and how does it involve chromic acid?

The Jones oxidation is a chemical reaction that uses chromic acid (typically as a mixture with sulfuric acid) to oxidize primary and secondary alcohols. In this reaction, primary alcohols are oxidized to carboxylic acids, while secondary alcohols are oxidized to ketones. The chromic acid serves as the oxidizing agent, with the chromium being reduced from Cr(VI) to Cr(III) in the process. This reaction is important in organic synthesis but has environmental drawbacks due to the use of chromium compounds.

11. How does the structure of chromic acid relate to its properties?

The structure of chromic acid consists of a central chromium atom bonded to four oxygen atoms, with two of these oxygen atoms also bonded to hydrogen. This tetrahedral arrangement contributes to its acidic nature and strong oxidizing properties. The Cr-O double bonds are particularly important for its oxidizing ability, as they can accept electrons during redox reactions.

12. Why is chromic acid considered unstable in its pure form?

Chromic acid is unstable in its pure form because it readily decomposes to form chromium trioxide (CrO3) and water. This instability is due to the high oxidation state of chromium (+6) and the tendency of the compound to release water molecules. As a result, chromic acid is typically handled in solution or as a mixture with sulfuric acid.

13. How does the color of chromic acid solutions change with concentration?

The color of chromic acid solutions changes with concentration due to the equilibrium between different chromium species. Dilute solutions appear yellow due to the presence of chromate ions (CrO4^2-). As the concentration increases, the color shifts to orange and then to red as dichromate ions (Cr2O7^2-) become more prevalent. This color change is an important visual indicator of the acid's concentration and oxidation state.

14. How does the pH of a chromic acid solution affect its properties?

The pH of a chromic acid solution significantly affects its properties. In strongly acidic conditions (low pH), the equilibrium shifts towards the formation of dichromate ions (Cr2O7^2-) and the solution becomes more orange-red. As the pH increases, the equilibrium shifts towards chromate ions (CrO4^2-), and the solution becomes more yellow. This pH-dependent behavior is crucial in understanding the acid's reactivity and applications.

15. What is the difference between chromic acid and dichromic acid?

Chromic acid (H2CrO4) and dichromic acid (H2Cr2O7) are related but distinct compounds. Chromic acid contains one chromium atom per molecule, while dichromic acid contains two. Dichromic acid is formed when chromic acid loses water in a condensation reaction: 2H2CrO4 → H2Cr2O7 + H2O. Both acids exhibit similar chemical properties, but dichromic acid is generally more stable.

16. What is the significance of the chromium oxidation state in chromic acid?

In chromic acid, chromium exists in its highest oxidation state of +6. This high oxidation state is crucial for the compound's properties, particularly its strong oxidizing ability. The Cr(VI) state allows chromic acid to accept electrons readily, making it an effective oxidizing agent. Understanding this concept helps in grasping the principles of oxidation states and their impact on chemical reactivity.

17. How does chromic acid behave as a diprotic acid?

Chromic acid (H2CrO4) is a diprotic acid, meaning it can donate two protons in acid-base reactions. In its first dissociation step, it releases one proton to form hydrogen chromate ion (HCrO4^-). In the second step, it releases another proton to form chromate ion (CrO4^2-). This stepwise dissociation is important in understanding the acid's behavior in solution and its role in various chemical reactions.

18. How does the concept of Lewis acids apply to chromic acid?

Chromic acid can act as a Lewis acid, which is defined as an electron pair acceptor. The central chromium atom, with its high oxidation state and empty d orbitals, can accept electron pairs from Lewis bases. This property contributes to chromic acid's ability to form complexes and its reactivity in various chemical processes. Understanding this concept helps in grasping the broader principles of acid-base chemistry beyond the traditional Brønsted-Lowry definition.

19. How does the electronic configuration of chromium influence the properties of chromic acid?

The electronic configuration of chromium, particularly in its +6 oxidation state in chromic acid, significantly influences its properties. The absence of d electrons in Cr(VI) makes it a strong oxidizing agent, as it can readily accept electrons to achieve a more stable d3 configuration of Cr(III). This electronic arrangement also affects the compound's color, reactivity, and ability to form complexes, all of which are crucial in understanding its chemical behavior.

20. What is the relationship between chromic acid and chromyl chloride?

Chromyl chloride (CrO2Cl2) is related to chromic acid as it can be considered a derivative where hydroxyl groups are replaced by chlorine atoms. Chromyl chloride can be prepared from chromic acid or chromates by reaction with hydrochloric acid. It shares some oxidizing properties with chromic acid but is more volatile. Understanding this relationship helps in grasping the versatility of chromium compounds and their interconversions.

21. What role does chromic acid play in organic chemistry?

In organic chemistry, chromic acid is a powerful oxidizing agent used to convert primary alcohols to aldehydes and secondary alcohols to ketones. It's particularly useful in the Jones oxidation reaction. However, its use has decreased due to environmental concerns, with more eco-friendly alternatives being preferred in modern organic synthesis.

22. What safety precautions should be taken when handling chromic acid?

Chromic acid is highly corrosive and toxic, requiring careful handling. Safety precautions include wearing appropriate personal protective equipment (PPE) such as gloves, goggles, and lab coats. Work should be conducted in a well-ventilated area or fume hood. Chromic acid should never be allowed to come into contact with skin or eyes, and any spills should be neutralized and cleaned up immediately following proper protocols.

23. What is chromic acid and why is it important in chemistry?

Chromic acid (H2CrO4) is an oxoacid of chromium in its highest oxidation state (+6). It's important in chemistry due to its strong oxidizing properties and its use in various industrial processes, such as electroplating and organic synthesis. Understanding chromic acid helps students grasp concepts of oxidation states, acid-base chemistry, and the behavior of transition metals.

24. Why is chromic acid considered a strong oxidizing agent?

Chromic acid is a strong oxidizing agent due to the high oxidation state of chromium (+6) and the stability of its reduced forms. The chromium atom can easily accept electrons, reducing from Cr(VI) to Cr(III). This property makes it effective in oxidizing various organic and inorganic compounds, often changing their chemical structure or properties in the process.

25. How does chromic acid interact with metals?

Chromic acid is highly reactive with most metals, causing rapid oxidation or corrosion. It can dissolve many metals, forming chromium(III) compounds and hydrogen gas. This property is utilized in metal etching and surface treatment processes. However, it also means that chromic acid must be stored in appropriate containers, typically made of glass or certain plastics, to prevent unwanted reactions.

26. What is the significance of chromic acid in electroplating?

Chromic acid plays a crucial role in electroplating, particularly in chromium plating. In this process, chromic acid serves as the electrolyte solution. When an electric current is passed through the solution, chromium is deposited onto the cathode, creating a hard, corrosion-resistant surface on various metals. This application is widely used in automotive and aerospace industries for both decorative and functional purposes.

27. How does chromic acid contribute to environmental concerns?

Chromic acid poses significant environmental concerns due to its toxicity and the persistence of chromium compounds in the environment. Chromium(VI) species, including those derived from chromic acid, are known carcinogens and can contaminate soil and water sources. Proper disposal and treatment of chromic acid waste are essential to prevent environmental pollution and protect ecosystems.

28. How does temperature affect the stability of chromic acid?

Temperature significantly affects the stability of chromic acid. At higher temperatures, chromic acid becomes more unstable and prone to decomposition. This decomposition can lead to the formation of chromium trioxide (CrO3) and water. The increased instability at higher temperatures is due to the enhanced molecular motion, which facilitates the breaking of bonds within the chromic acid molecule.

29. How does chromic acid compare to other common oxidizing agents?

Chromic acid is a strong oxidizing agent, often compared to other oxidizers like potassium permanganate (KMnO4) or hydrogen peroxide (H2O2). While all these compounds can oxidize various substances, chromic acid is particularly effective for certain organic oxidations. However, it's generally more hazardous and environmentally problematic than some alternatives, leading to a decrease in its use in favor of more eco-friendly options in modern chemistry.

30. What role does chromic acid play in analytical chemistry?

In analytical chemistry, chromic acid is used in various applications. It's employed in titrimetric analysis for determining the concentration of reducing agents. Chromic acid can also be used in the detection and quantification of certain organic compounds, particularly alcohols. Its strong oxidizing properties make it useful in breaking down organic matter for analysis, though safer alternatives are often preferred in modern analytical methods.

31. What is the significance of chromic acid in the leather tanning industry?

Chromic acid and its derivatives play a crucial role in the leather tanning industry. Chromium(III) compounds, often derived from the reduction of chromic acid, are used in chrome tanning. This process creates strong cross-links in collagen fibers, resulting in leather that is more durable, flexible, and resistant to decay. Understanding this application helps in grasping the practical importance of chromium chemistry in industrial processes.

32. How does chromic acid participate in redox reactions?

In redox reactions, chromic acid acts as a strong oxidizing agent. The chromium in chromic acid is reduced from its +6 oxidation state to +3, while the substance being oxidized loses electrons. This electron transfer is the essence of redox reactions. For example, in the oxidation of alcohols, the chromium in chromic acid accepts electrons, reducing to Cr(III), while the alcohol loses electrons, becoming oxidized to an aldehyde or ketone.

33. What are the environmental regulations concerning the use and disposal of chromic acid?

Environmental regulations for chromic acid are stringent due to its toxicity and environmental impact. Many countries have strict guidelines for its use, storage, and disposal. Chromium(VI) compounds, including chromic acid, are classified as hazardous waste. Proper neutralization and treatment are required before disposal, and many industries are required to implement chromium recovery systems. These regulations aim to prevent water and soil contamination and protect human health and ecosystems.

34. How does chromic acid interact with organic compounds containing double bonds?

Chromic acid can react with organic compounds containing double bonds through a process called oxidative cleavage. In this reaction, the double bond is broken, and each carbon involved in the bond is oxidized. For example, an alkene can be cleaved to form two carbonyl compounds (aldehydes or ketones). This reaction is useful in organic synthesis for breaking carbon-carbon double bonds and introducing oxygen-containing functional groups.

35. What is the role of chromic acid in corrosion resistance treatments?

Chromic acid is used in corrosion resistance treatments, particularly for metals like aluminum. In a process called chromate conversion coating, the metal surface is treated with a chromic acid solution, forming a thin, protective layer of chromium compounds. This layer enhances the metal's resistance to corrosion and improves paint adhesion. However, due to environmental concerns, many industries are shifting towards more eco-friendly alternatives.

36. What is the significance of chromic acid in the production of chromium pigments?

Chromic acid plays a role in the production of various chromium pigments, which are widely used in paints, inks, and plastics. While chromic acid itself is not a pigment, it can be a starting material for producing chromium(III) compounds that serve as pigments. The vibrant colors of these pigments, ranging from yellows to greens, are due to the electronic transitions in chromium ions. Understanding this application helps in connecting theoretical concepts of electron configuration to practical color chemistry.

37. How does chromic acid behave in non-aqueous solvents?

The behavior of chromic acid in non-aqueous solvents can differ significantly from its behavior in water. In some organic solvents, it may not dissociate as readily, affecting its acidity and oxidizing power. The choice of solvent can influence the reactivity and selectivity of chromic acid in organic reactions. This concept is important in understanding how solvent effects can modify the properties and reactivity of acids and oxidizing agents.

38. How does chromic acid affect the human body if exposed?

Exposure to chromic acid can have severe health effects on the human body. It is corrosive to skin and mucous membranes, causing burns and ulcerations. Inhalation of chromic acid mist can damage the respiratory system. Long-term exposure is associated with increased cancer risk, particularly lung cancer. Chromium(VI) compounds from chromic acid can also cause kidney and liver damage. This toxicity underscores the importance of proper handling and safety measures in chemistry labs and industrial settings.

39. What is the role of chromic acid in the passivation of stainless steel?

Chromic acid is used in the passivation process for stainless steel, enhancing its corrosion resistance. During passivation, the chromic acid solution removes free iron from the surface and promotes the formation of a thin, protective chromium oxide layer. This layer makes the steel "passive" or less reactive to further corrosion. Understanding this process helps in grasping the practical applications of oxidation-reduction reactions in materials science.

40. How does the concept of resonance apply to the chromate ion derived from chromic acid?

The chromate ion (CrO4^2-), derived from chromic acid, exhibits resonance structures. The four oxygen atoms are equivalent due to resonance, with the negative charge distributed equally among them. This resonance stabilization contributes to the stability and properties of chromate compounds. Understanding this concept helps in grasping the principles of molecular structure and bonding in inorganic compounds.

41. What is the significance of chromic acid in forensic science?

In forensic science, chromic acid has been used in various applications, including the detection of blood stains and the analysis of certain types of evidence. Its strong oxidizing properties can be utilized in chemical tests and in the preparation of samples for analysis. However, due to its toxicity, its use in forensics has been largely replaced by safer alternatives. This application demonstrates the intersection of