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Send EmailChromic Acid, Chromium Trioxide, Chromium Anhydride, Dichromic Acid, 7738-94-5
CHROMIC ACID (H₂CrO₄ / CrO₃)
Chromium Trioxide / Chromium Anhydride / Dichromic Acid
CAS Number: 7738-94-5
EC Number: 231-801-5
1. IDENTIFICATION
| Property | Information |
|---|---|
| Chemical Name | Chromic Acid |
| Synonyms | Chromium trioxide, Chromium(VI) oxide, Chromium anhydride, Dichromic acid, Chromic(VI) acid |
| Chemical Formula | H₂CrO₄ (in solution) / CrO₃ (anhydrous solid) |
| Molecular Weight | 118.01 g/mol (H₂CrO₄) / 99.99 g/mol (CrO₃) |
| CAS Number | 7738-94-5 |
| EC Number (EINECS) | 231-801-5 |
| Appearance | Dark red to purple-red crystalline solid (CrO₃) / Orange solution (H₂CrO₄) |
| Odor | Odorless |
2. PHYSICAL PROPERTIES
| Property | Value |
|---|---|
| Physical State (20°C) | Solid (crystalline) – CrO₃ |
| Appearance | Dark red to purple-red, deliquescent crystals |
| Odor | Odorless |
| Molecular Weight (CrO₃) | 99.99 g/mol |
| Molecular Weight (H₂CrO₄) | 118.01 g/mol |
| Density (20°C) | 2.70 g/cm³ |
| Melting Point | 196 °C (385 °F) |
| Boiling Point | Decomposes above 250°C |
| Solubility in Water (20°C) | Very high (166 g/100 mL) |
| Solubility in Acids | Soluble |
| pH (1 mM solution) | 3.03 |
| pH (10 mM solution) | 2.33 |
| pH (100 mM solution) | 2.06 |
| Vapor Pressure | Negligible |
| Hygroscopicity | Very hygroscopic (deliquescent – absorbs moisture from air) |
3. CHEMICAL PROPERTIES
| Property | Information |
|---|---|
| Chemical Formula | H₂CrO₄ (in solution) / CrO₃ (anhydrous solid) |
| Molecular Weight | 118.01 g/mol (H₂CrO₄) |
| Chromium (Cr) Content | ~44.0% (as Cr(VI)) |
| Oxidation State | Cr(VI) (hexavalent chromium) – highly toxic and carcinogenic |
| pH (1% solution) | ~2.0 – 3.0 (strongly acidic) |
| Acid Strength | Strong acid (pKa1 = 4.1, pKa2 = 3.2 × 10⁻⁷) |
| Stability | Stable under normal conditions |
| Oxidizing Properties | Very strong oxidizer |
| Reaction with Water | CrO₃ + H₂O → H₂CrO₄ (exothermic) |
| Reaction with Organics | Violent reactions, may cause fire or explosion |
| Incompatible Materials | Organic materials, reducing agents, combustible materials, alcohols, acetone, glycerol |
Equilibrium in Solution:
2 CrO₄²⁻ (yellow) + 2 H⁺ ⇌ Cr₂O₇²⁻ (orange) + H₂O (K = 4.2 × 10¹⁴)
-
Acidic solution: Cr₂O₇²⁻ (orange-red, dichromate dominant)
-
Alkaline solution: CrO₄²⁻ (yellow, chromate dominant)
Reaction with Alcohols:
2 H₂CrO₄ + 3 CH₃CH₂OH + 6 H⁺ → 2 Cr³⁺ + 3 CH₃CHO + 8 H₂O
4. TYPES & GRADES
| Grade | Purity (CrO₃) | Form | Applications |
|---|---|---|---|
| Technical Grade | ≥ 99.0% | Crystalline | Electroplating, metal finishing |
| Reagent Grade | ≥ 99.5% | Crystalline | Laboratory, analytical chemistry |
| High Purity Grade | ≥ 99.9% | Crystalline | Specialty applications, research |
| Chromic Acid Solution | Various concentrations | Liquid (aqueous) | Cleaning solutions, electroplating baths |
5. PRODUCTION PROCESS
| Stage | Description |
|---|---|
| 1. Raw Material | Sodium dichromate (Na₂Cr₂O₇) or potassium dichromate (K₂Cr₂O₇) |
| 2. Acidification | Sodium dichromate is reacted with concentrated sulfuric acid (H₂SO₄) |
| 3. Reaction | Na₂Cr₂O₇ + H₂SO₄ → 2 CrO₃ + Na₂SO₄ + H₂O |
| 4. Crystallization | Chromium trioxide (CrO₃) crystallizes |
| 5. Centrifugation | Crystals are separated from mother liquor |
| 6. Drying | Crystals are dried at controlled temperature |
| 7. Packaging | Product is packaged (airtight, moisture-proof containers) |
Reaction Equation:
Na₂Cr₂O₇ + H₂SO₄ → 2 CrO₃ + Na₂SO₄ + H₂O
6. APPLICATIONS
6.1. Electroplating (Chrome Plating) – Largest Use (~70%)
| Application | Function |
|---|---|
| Decorative Chrome Plating | Provides bright, shiny finish on automotive parts, faucets, hardware |
| Hard Chrome Plating (Industrial) | Increases wear resistance, hardness, and corrosion protection |
| Electroplating Bath | CrO₃ + H₂SO₄ + H₂O → Chrome plating electrolyte |
| Anodizing | Sealing of anodized aluminum surfaces |
Typical Hard Chrome Plating Bath Composition:
-
200-300 g/L CrO₃
-
2-3 g/L H₂SO₄
-
Current density: 20-50 A/dm²
-
Temperature: 50-60°C
6.2. Laboratory Cleaning Solutions
| Application | Function |
|---|---|
| Chromic Acid Cleaning Solution | Removal of organic residues from glassware (sodium dichromate + H₂SO₄) |
| Glassware Decontamination | Oxidizes organic contaminants, leaves glassware clean |
Note: Due to toxicity, use is being phased out in favor of safer alternatives (detergents, NOCHROMIX).
6.3. Wood Preservation
| Application | Function |
|---|---|
| Wood Treatment | Protects against decay, fungal growth, and insect damage |
| CCA Alternative | Component in some wood preservative formulations |
6.4. Pigment Production
| Application | Function |
|---|---|
| Chrome Yellow | PbCrO₄ – yellow pigment for paints, plastics, inks |
| Chrome Orange | Orange pigment |
| Chrome Green | Mixed pigment |
6.5. Leather Tanning (Auxiliary)
| Application | Function |
|---|---|
| Chrome Tanning | Used as an intermediate in basic chromium sulfate production |
| Hide Processing | Provides softness and durability to leather |
6.6. Catalyst & Chemical Synthesis
| Application | Function |
|---|---|
| Oxidation Catalyst | Catalyzes oxidation reactions in organic synthesis |
| Chemical Intermediate | Raw material for other chromium compounds |
| Pesticide Production | Intermediate for certain pesticides |
6.7. Metal Finishing
| Application | Function |
|---|---|
| Passivation | Forms protective oxide layer on metals |
| Corrosion Inhibition | Prevents rust and corrosion on metal surfaces |
| Etching | Metal surface preparation |
6.8. Other Applications
| Application | Function |
|---|---|
| Battery Manufacturing | Component in some battery types |
| Pyrotechnics | Oxidizing agent in fireworks |
| Magnetic Tape Production | Abrasive component |
| Textile Dyeing | Mordant for fabric dyes |
7. CHROMIC ACID CLEANING SOLUTION
| Parameter | Information |
|---|---|
| Composition | Sodium dichromate (Na₂Cr₂O₇) + concentrated H₂SO₄ |
| Appearance | Dark red solution |
| Function | Oxidizes organic residues – leaves glassware clean |
| Safety | Extremely corrosive, toxic, carcinogenic |
| Alternatives | Detergents, NOCHROMIX, alkaline cleaners |
8. QUALITY SPECIFICATIONS (TECHNICAL GRADE – CrO₃)
| Parameter | Specification |
|---|---|
| Purity (CrO₃) | ≥ 99.0% |
| Cr(VI) Content | ~68.0% |
| Sulfate (SO₄) | ≤ 0.10% |
| Chlorides (Cl) | ≤ 0.005% |
| Iron (Fe) | ≤ 0.01% |
| Water Insolubles | ≤ 0.05% |
| Moisture | ≤ 0.5% |
9. STORAGE & HANDLING
| Parameter | Information |
|---|---|
| Storage Conditions | Cool, dry, well-ventilated area |
| Container Requirements | Tightly closed, moisture-proof, corrosion-resistant containers (HDPE, stainless steel, glass) |
| Protect From | Moisture (deliquescent), organic materials, reducing agents, heat |
| Shelf Life | 12-24 months (when stored properly in unopened, airtight containers) |
| Hygroscopicity | Very hygroscopic – absorbs moisture from air |
| Incompatible Materials | Organic materials, reducing agents, combustible materials, alcohols, acetone, glycerol |
| Packaging Options | 25 kg drums (HDPE), 50 kg drums, 500 kg/1000 kg FIBC (big bags) |
10. SAFETY & HEALTH INFORMATION (GHS CLASSIFICATION)
| Hazard Class | Category |
|---|---|
| Oxidizing Solids | Category 1 (H271) |
| Acute Toxicity (Oral) | Category 3 (H301) |
| Acute Toxicity (Inhalation) | Category 2 (H330) |
| Acute Toxicity (Dermal) | Category 3 (H311) |
| Skin Corrosion/Irritation | Category 1B (H314) |
| Serious Eye Damage | Category 1 (H318) |
| Respiratory Sensitization | Category 1 (H334) |
| Skin Sensitization | Category 1 (H317) |
| Germ Cell Mutagenicity | Category 1B (H340) |
| Carcinogenicity | Category 1A (H350) |
| Reproductive Toxicity | Category 2 (H361) |
| Specific Target Organ Toxicity (Repeated exposure) | Category 1 (H372) |
| Acute Aquatic Toxicity | Category 1 (H400) |
| Chronic Aquatic Toxicity | Category 1 (H410) |
11. HAZARD STATEMENTS (H-CODES)
| Code | Statement |
|---|---|
| H271 | May cause fire or explosion; strong oxidizer |
| H301 | Toxic if swallowed |
| H311 | Toxic in contact with skin |
| H314 | Causes severe skin burns and eye damage |
| H317 | May cause an allergic skin reaction |
| H318 | Causes serious eye damage |
| H330 | Fatal if inhaled |
| H334 | May cause allergy or asthma symptoms if inhaled |
| H340 | May cause genetic defects |
| H350 | May cause cancer |
| H361 | Suspected of damaging fertility or the unborn child |
| H372 | Causes damage to organs through prolonged or repeated exposure |
| H400 | Very toxic to aquatic life |
| H410 | Very toxic to aquatic life with long-lasting effects |
12. PRECAUTIONARY STATEMENTS (P-CODES)
| Code | Statement |
|---|---|
| P201 | Obtain special instructions before use |
| P202 | Do not handle until all safety precautions have been read and understood |
| P210 | Keep away from heat, sparks, open flames |
| P220 | Keep away from combustible materials |
| P260 | Do not breathe dust |
| P280 | Wear protective gloves, protective clothing, eye protection, face protection |
| P301+P310 | IF SWALLOWED: Immediately call a POISON CENTER |
| P302+P352 | IF ON SKIN: Wash with plenty of water |
| P304+P340 | IF INHALED: Remove person to fresh air |
| P305+P351+P338 | IF IN EYES: Rinse cautiously with water for several minutes |
| P308+P313 | IF exposed or concerned: Get medical advice |
| P501 | Dispose of contents/container in accordance with local regulations |
13. TOXICOLOGICAL INFORMATION
| Parameter | Value |
|---|---|
| Oral LD50 (rat) | ~80 mg/kg (highly toxic) |
| Inhalation TCL0 (human) | 20 mg/m³ (irritation, respiratory effects) |
| Carcinogenicity | IARC Group 1 (Carcinogenic to humans) |
| Mutagenicity | Positive – causes genetic mutations |
| Reproductive Toxicity | Suspected reproductive toxicant |
| Target Organs | Respiratory system, skin, eyes, kidneys, liver |
| Chronic Effects | Lung cancer, nasal septum perforation, dermatitis, kidney damage |
Health Effects:
-
Acute (Ingestion): Nausea, vomiting, diarrhea, abdominal pain, gastrointestinal bleeding, acute renal failure
-
Acute (Inhalation): Respiratory tract irritation, coughing, wheezing, pulmonary edema
-
Acute (Skin Contact): Severe burns, dermatitis, sensitization
-
Acute (Eye Contact): Severe burns, potential blindness
-
Chronic: Lung cancer, nasal ulcers and perforation, chronic dermatitis, kidney damage
14. FIRST AID MEASURES
| Exposure Route | Action |
|---|---|
| Inhalation | Remove to fresh air. Administer oxygen if breathing difficulty. Seek immediate medical attention. |
| Skin Contact | Remove contaminated clothing. Wash with plenty of water for at least 15 minutes. Seek medical attention. |
| Eye Contact | Rinse immediately with plenty of water for at least 15 minutes. Seek immediate medical attention. |
| Ingestion | Do NOT induce vomiting. Rinse mouth. Drink water. Seek immediate medical attention. |
15. FIRE FIGHTING MEASURES
| Parameter | Information |
|---|---|
| Fire Hazard | Strong oxidizer – may cause fire or explosion when in contact with combustible materials |
| Extinguishing Media | Water spray (large quantities), dry sand, CO₂ (for small fires) |
| Special Hazards | Decomposes when heated, releasing toxic chromium fumes and oxygen |
| Protective Equipment | Self-contained breathing apparatus (SCBA), full protective clothing |
16. ENVIRONMENTAL INFORMATION
| Parameter | Information |
|---|---|
| Aquatic Toxicity | Very toxic to aquatic life (fish, algae, invertebrates) |
| Persistence | Persistent in environment (Cr(VI) does not degrade) |
| Bioaccumulation | Moderate potential |
| Mobility in Soil | High (soluble in water) |
| Waste Disposal | Dispose as hazardous waste according to local regulations. Do not discharge into natural water bodies. |
17. TRANSPORT INFORMATION
| Parameter | Information |
|---|---|
| UN Number | 1463 (Chromium trioxide, anhydrous) |
| Hazard Class | 5.1 (Oxidizing substance) |
| Subsidiary Hazard | 6.1 (Toxic substance) |
| Packing Group | II |
| Proper Shipping Name | CHROMIUM TRIOXIDE, ANHYDROUS |
| Marine Pollutant | Yes |
| ADR/RID Label | 5.1 + 6.1 |
| EMS | F-A, S-Q |
18. REGULATORY INFORMATION
| Region | Status |
|---|---|
| EU | REACH registered; restricted under Annex XVII (SVHC – Substance of Very High Concern) |
| Turkey (KKDIK) | Mandatory compliance; requires registration |
| USA (TSCA) | Listed; subject to reporting |
| Canada (DSL) | Listed |
| Australia (AICS) | Listed |
| Japan (ENCS) | Listed |
| Korea (KECL) | Listed |
| China (IECSC) | Listed |
| RoHS | Restricted in electrical and electronic equipment |
19. SYNONYMS & OTHER NAMES
| Turkish Name | English Name |
|---|---|
| Kromik Asit | Chromic Acid |
| Krom Trioksit | Chromium Trioxide |
| Krom(VI) Oksit | Chromium(VI) Oxide |
| Krom Anhidrit | Chromium Anhydride |
| Dikromik Asit | Dichromic Acid |
Database Identifiers:
-
CAS: 7738-94-5
-
EC: 231-801-5
-
MDL: MFCD00010952
-
PubChem CID: 14915
-
RTECS: GB6650000
-
UN: 1463
20. SUMMARY & IMPORTANT NOTES
SUMMARY:
Chromic Acid (H₂CrO₄ / CrO₃, CAS 7738-94-5) is a dark red to purple-red, crystalline, highly toxic, and strong oxidizing agent containing hexavalent chromium (Cr(VI)). It is classified as an IARC Group 1 carcinogen and is extremely hazardous to human health and the environment.
Key Features:
| Feature | Value |
|---|---|
| Appearance | Dark red to purple-red crystalline solid |
| Molecular Weight (CrO₃) | 99.99 g/mol |
| Density | 2.70 g/cm³ |
| Melting Point | 196°C |
| Water Solubility | Very high (166 g/100 mL) |
| Oxidizing Class | Strong oxidizer (UN 1463, Class 5.1 + 6.1) |
Main Application Areas:
| Sector | Applications |
|---|---|
| Electroplating | Decorative and hard chrome plating |
| Laboratory | Glassware cleaning (chromic acid solution) |
| Wood Preservation | Fungicide, insecticide |
| Pigments | Chrome yellow, chrome orange |
| Leather Tanning | Chrome tanning (intermediate) |
| Catalyst | Oxidation reactions |
Key Safety Points:
-
CARCINOGEN (Category 1A) – May cause cancer (lung cancer)
-
MUTAGEN – May cause genetic defects
-
TOXIC – Fatal if swallowed, inhaled, or in contact with skin
-
CORROSIVE – Causes severe skin burns and eye damage
-
ENVIRONMENTAL HAZARD – Very toxic to aquatic life
-
STRONG OXIDIZER – Keep away from combustible materials
-
HANDLE WITH EXTREME CAUTION – Use full PPE, adequate ventilation
Important Disclaimer: This Technical Data Sheet (TDS) is for informational purposes only. For complete safety, handling, storage, and regulatory compliance information, always refer to the official Safety Data Sheet (SDS) provided by the manufacturer/supplier. Chromic acid is an extremely hazardous substance. Extreme caution must be exercised during handling, storage, and disposal.
