Chromic acid is a strong and corrosive oxidizing agent used in various applications, such as metal cleaning, etching, and in some laboratory experiments. It has red color.
| IUPAC Name | Chromic Acid |
| Molecular Formula | H2CrO4 |
| CAS Number | 7738-94-5 |
| Synonyms | Chromium(VI) Acid, Chromium Acid, dihydroxidodioxidochromium, dihydrogen(tetraaoxidochromate) |
| InChI | InChI=1S/Cr.H2O4/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 |
Chromic Acid Properties
Chromic Acid Formula
The chemical formula of chromium acid is H2CrO4. It consists of two hydrogen atoms, one chromium atom, and four oxygen atoms. The formula represents the composition of chromium acid on a molecular level.
Chromic Acid Molar Mass
The molar mass of chromium acid can be calculated by adding up the atomic masses of its constituent elements. Chromium has an atomic mass of 51.996 grams per mole, hydrogen has a molar mass of 1.008 grams per mole, and oxygen has a molar mass of 16.00 grams per mole. Therefore, the molar mass of chromium acid is approximately 118.00 grams per mole.
Chromic Acid Boiling Point
Chromium acid does not have a distinct boiling point since it decomposes upon heating, releasing oxygen gas. However, its decomposition temperature is around 190°C (374°F). When heated, chromium acid undergoes a chemical reaction that results in the formation of chromium trioxide and water.
Chromic Acid Melting Point
The melting point of chromium acid is not well-defined due to its tendency to decompose before melting. However, it is known that chromium acid can decompose around 250°C (482°F) or even lower temperatures, depending on the conditions.
Chromic Acid Density g/mL
Chromium acid has a density of approximately 1.2 grams per milliliter (g/mL) at room temperature. This density value indicates that chromium acid is relatively dense compared to water.
Chromic Acid Molecular Weight
The molecular weight of chromium acid is calculated by summing the atomic masses of its constituent elements. In this case, the molecular weight is approximately 118.00 grams per mole.
Chromic Acid Structure
The structure of chromium acid is represented by a central chromium atom bonded to four oxygen atoms and two hydrogen atoms. The oxygen atoms are arranged around the chromium atom in a tetrahedral shape.
Chromic Acid Solubility
Chromium acid is moderately soluble in water, meaning it can dissolve to some extent. The solubility increases with increasing temperature. However, it should be handled with caution as it is a corrosive substance.
| Appearance | Dark red crystals |
| Specific Gravity | 2.70 |
| Color | Red |
| Odor | Odorless |
| Molar Mass | 118.01 g/mol |
| Density | 1.201 g/mL |
| Melting Point | Decomposes at ~190°C |
| Boiling Point | Decomposes at ~250°C |
| Flash Point | Not applicable |
| Water Solubility | Soluble |
| Solubility | Soluble in water and organic solvents such as ethanol, ether |
| Vapour Pressure | Not applicable |
| Vapour Density | Not applicable |
| pKa | -0.64 |
| pH | Highly acidic (pH < 1) |
Chromic Acid Safety and Hazards
Chromium acid poses several safety hazards and should be handled with caution. It is a corrosive substance that can cause severe burns to the skin, eyes, and respiratory system upon contact. Inhaling chromium acid fumes or mist can irritate the respiratory tract and lead to coughing, shortness of breath, and lung damage. It is also highly toxic if ingested, causing abdominal pain, vomiting, and potential organ damage. Moreover, chromium acid is a strong oxidizing agent and can react violently or ignite flammable substances. Proper protective equipment, such as gloves, goggles, and a lab coat, should be worn when working with chromium acid, and it should be stored and disposed of in accordance with safety regulations.
| Hazard Symbols | Corrosive, Oxidizing |
| Safety Description | – Causes severe burns – May intensify fire; oxidizer – Harmful if swallowed – Causes respiratory irritation – Causes eye damage – May cause genetic defects – May cause cancer – May damage fertility or the unborn child – Very toxic to aquatic life – Handle and dispose of properly |
| UN IDs | UN1755, UN1463 |
| HS Code | 28191000 |
| Hazard Class | 8 (Corrosive) |
| Packing Group | II (Intermediate) |
| Toxicity | Highly toxic and harmful |
Chromic Acid Synthesis Methods
There are several methods for synthesizing chromium acid.
One common method involves the reaction between sodium dichromate (Na2Cr2O7) and sulfuric acid (H2SO4). In this process, you slowly add sodium dichromate to the sulfuric acid while stirring. The reaction proceeds to form chromium acid (H2CrO4) and sodium sulfate (Na2SO4) as a byproduct. The resulting chromium acid solution can be purified and concentrated by removing excess water.
Similar to the previous method, we can add potassium chromate to sulfuric acid, resulting in the formation of chromium acid and potassium sulfate (K2SO4) as a byproduct.
Alternatively, you can prepare chromium acid by reacting chromium trioxide (CrO3) with water. You dissolve the chromium trioxide in water, resulting in the formation of a chromium acid solution.
Remember that chromium acid is a highly corrosive and hazardous substance. Therefore, one should carry out its synthesis with proper safety precautions and in a well-ventilated area. Wear protective equipment, such as gloves, goggles, and a lab coat, during the synthesis process. Also, follow proper disposal methods to ensure the safe handling and disposal of any waste generated during the synthesis.
Chromic Acid Uses
Chromium acid finds various applications due to its properties as a strong oxidizing agent. Here are some common uses:
- Metal cleaning: Chromium acid effectively removes rust, scale, and organic deposits from metal surfaces, cleaning and removing surface contaminants.
- Etching: Chromium acid creates fine patterns and designs on surfaces, such as glass, ceramics, and metals, etching them and making it useful in decorative glassware production and electronic circuitry manufacturing.
- Surface preparation: Industrial processes employ chromium acid to prepare surfaces for painting, coating, or bonding, ensuring proper adhesion by removing impurities and creating a clean surface.
- Analytical chemistry: Chemists and laboratories use chromium acid as an oxidizing agent in chemical analysis and laboratory experiments, determining the concentrations of certain organic compounds.
- Wood preservation: Chromium acid acts as a wood preservative, penetrating deep into wood fibers to protect against decay, insect infestation, and weathering.
- Textile industry: The textile manufacturing industry utilizes chromium acid for dyeing and printing processes, fixing dyes in fabric and enhancing color fastness.
- Photography: Chromium acid plays a role in certain photographic processes, including the production of color prints and color reversal films.
- Electroplating: In electroplating processes, especially for chromium plating, chromium acid serves as a source of chromium ions that deposit on metal surfaces, providing a protective and decorative coating.
It’s important to note that chromium acid is a hazardous substance, and proper safety precautions should be taken during its handling, storage, and disposal.
Questions:
Q: What happens when phenol is oxidized with chromic acid?
A: Phenol undergoes oxidation with chromium acid, resulting in the formation of quinones and water.
Q: How to prepare chromic acid?
A: Chromium acid can be prepared by reacting sodium dichromate or potassium chromate with sulfuric acid.
Q: How to make chromic acid?
A: Chromium acid can be made by mixing a chromium compound (such as chromium trioxide) with water.
Q: What is chromic acid?
A: Chromium acid is a strong and corrosive oxidizing agent composed of chromium, hydrogen, and oxygen.
Q: Does chromic acid reduce alkenes?
A: No, chromium acid is an oxidizing agent and does not have reducing properties.
Q: How to prepare chromic acid for cleaning laboratory glassware?
A: Chromium acid cleaning solution can be prepared by dissolving chromium trioxide in water and adding sulfuric acid.
Q: Is chromic acid a strong acid?
A: Yes, chromium acid is considered a strong acid due to its ability to donate protons.
Q: How to prepare chromic acid cleaning solution?
A: To prepare a chromium acid cleaning solution, dissolve chromium trioxide in water and add a small amount of sulfuric acid.
Q: Which of the following alcohols will give a positive chromic acid test?
A: Primary alcohols can give a positive chromium acid test, producing a color change from orange to green or blue.