What is Chromic Acid Definition Formula Reactions and Uses
Chromic acid is a really strong oxidizing agent that is brought into use for oxidising diverse classes of organic compounds. The most common of these compounds are alcohols. Also, chromic acid is used to designate a mixture that is prepared by mixing dichromate and concentrated sulphuric acid. This type of acid is used as a cleaning mixture for washing glass. It can also refer to the molecular class, H2CrO4. This molecular acid has lots in common with sulphuric acid, H2SO4. Chromic acid is also known by the name of Tetraoxo Chromic acid or Chromic(VI) acid.
Chromic Acid Formula
Chromic acid is the conjugate acid of hydrogen chromate and it possesses chromium in an oxidation number of +6 (or VI). The chromic acid formula is H2CrO4:
IUPAC Name: Chromic Acid.
Chronic Acid Formula: H2CrO4.
The Simplified Molecular-Input Line-Entry System (SMILES): O[Cr](=O)(=O)O
Density: 1.201 g cm.
Melting Point: 197 °C.
Chromic Acid Boiling Point: 250 °C,
Chromic Acid Molecular Weight: 118.01 g/mol
Chromic Acid Preparation
Since chromic acid is known to be highly toxic, it is advisable not to make large portions of it and then store it for a larger period of time. Also, when you are working with any reagent, it is always better to wear proper equipment, for example, gloves, coat, etc. Besides, make sure that you ventilate the room where the acid is to be prepared properly.
Step 1: Get a clean litre flask or a beaker. Fill the beaker with 20 grams Sodium dichromate (Na2Cr2O7) or potassium dichromate (K2Cr2O7).
Step 2: Add some water to the beaker or the flask and then stir it using a glass stirring rod in order to make a paste.
Step 3: when you are stirring, pour 300 ml of concentrated sulfuric acid (H2SO4 (aq)) to the beaker.
Step 4: Pour this prepared chromic acid to a glass container having a stopper. Make sure that you put a label to this beaker and also put the date when it was made.
Chromic Acid Structure
The chromic acid structure is as follows:
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The chromic acid structure includes chromium having an oxidation state of +6 (or VI). Also, the chromic acid splits as:
H2CrO4 ⇌ [HCrO4]- + H+
Different Uses of Chromic Acid
Chromic acid is used as an intermediate for the chromium plating process.
It is also used for coloured glasses and ceramic glazes.
Chromic acid is also used for cleaning laboratory glassware.
It was also used as a hair dye in the year 1940.
It can be used for brightening raw brass and it is thus also used in the instrument repair field, especially the musical instrument repair industry.
It is used as a bleach in photographic reversal procedure.
The said chromic acid can oxidise different forms of organic compounds. Thus, you can find diverse variants being created for this particular reagent. It is also referred to as the Jones reagent in different aqueous sulfuric acid as well as acetone. This oxidises primary as well as secondary alcohols into ketones and carboxylic acids.
Health Hazards of Chromic Acid
Chromic acid which comes under hexavalent chromium compounds is highly toxic as well as carcinogenic. Thus, chromic acid oxidation is used mainly in the aerospace field and not in any other industry. This acid is a strong oxidiser and can react violently if you combine it with some easily oxidisable substance and can even cause some explosion.
Chromic Acid Reactions
Chromic acid can oxidise different types of organic compounds and thus diverse reagent variations can be developed:
Chromic acid in acetone and sulfuric acid is called Jones reagent.
Collins reagent is basically an adduct of pyridine and chromium trioxide which is used for different oxidations.
Chromyl chloride or CrO2Cl2 is also a molecular compound that can be generated from chromic acid.
FAQs on Chromic Acid Structure Preparation and Properties
1. What is chromic acid?
Chromic acid is a strong oxidizing acid of chromium with the formula H2CrO4, commonly formed when chromium(VI) oxide dissolves in water.
- It contains chromium in the +6 oxidation state.
- In aqueous solution, it exists in equilibrium with dichromic acid (H2Cr2O7) and dichromate ions.
- It is widely used in organic oxidation reactions and laboratory cleaning solutions.
2. What is the formula of chromic acid?
The chemical formula of chromic acid is H2CrO4.
- It consists of two hydrogen atoms, one chromium atom, and four oxygen atoms.
- Chromium is in the +6 oxidation state.
- It is related to the chromate ion CrO42−, which forms when chromic acid loses two protons.
3. How is chromic acid prepared?
Chromic acid is prepared by dissolving chromium(VI) oxide in water. The reaction is:
- CrO3(s) + H2O(l) → H2CrO4(aq)
- 2CrO42−(aq) + 2H+(aq) ⇌ Cr2O72−(aq) + H2O(l)
4. Why is chromic acid a strong oxidizing agent?
Chromic acid is a strong oxidizing agent because chromium in the +6 oxidation state is easily reduced to +3.
- It gains electrons during redox reactions.
- In acidic medium, it is reduced from Cr(VI) to Cr3+.
- This large change in oxidation state makes it effective in oxidizing alcohols and other organic compounds.
5. How does chromic acid oxidize alcohols?
Chromic acid oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones under acidic conditions.
- Primary alcohol example: 3CH3CH2OH + 2CrO3 + 6H+ → 3CH3COOH + 2Cr3+ + 6H2O
- Secondary alcohols form ketones.
- Tertiary alcohols generally do not react due to lack of an oxidizable hydrogen.
6. What is the difference between chromic acid and dichromic acid?
Chromic acid (H2CrO4) and dichromic acid (H2Cr2O7) differ in the number of chromium atoms and exist in equilibrium in solution.
- H2CrO4 contains one chromium atom.
- H2Cr2O7 contains two chromium atoms.
- They interconvert depending on pH and concentration.
7. What is the oxidation state of chromium in chromic acid?
The oxidation state of chromium in H2CrO4 is +6.
- Hydrogen is +1 each (total +2).
- Oxygen is −2 each (total −8).
- Let chromium be x: x + 2 − 8 = 0, so x = +6.
8. What are the uses of chromic acid?
Chromic acid is used mainly as an oxidizing agent and in surface treatment processes.
- Oxidation of alcohols in organic synthesis.
- Cleaning laboratory glassware (chromic acid cleaning solution).
- Electroplating and metal surface treatment.
9. Is chromic acid dangerous?
Yes, chromic acid is highly toxic, corrosive, and carcinogenic because it contains hexavalent chromium.
- It can cause severe skin burns and eye damage.
- Inhalation or ingestion may lead to serious health effects.
- It is also an environmental pollutant due to Cr(VI) compounds.
10. How does pH affect the chromate–dichromate equilibrium?
The chromate–dichromate equilibrium shifts toward dichromate in acidic solution and toward chromate in basic solution. The equilibrium reaction is:
- 2CrO42−(aq) + 2H+(aq) ⇌ Cr2O72−(aq) + H2O(l)
- In acidic medium: more Cr2O72− (orange).
- In basic medium: more CrO42− (yellow).
