Chromium-compound manufacture
- Process role: Cr(VI) intermediate
- Critical parameters: Hydration state; assay; impurity profile; regulatory status
Sodium Dichromate (Na₂Cr₂O₇)
Sodium dichromate is a highly hazardous hexavalent-chromium oxidizer used as an intermediate or process chemical in selected chromium chemistry, surface treatment and specialty industrial operations. Anhydrous and dihydrate forms must be distinguished explicitly: they have different CAS numbers and molar masses. Procurement is dominated by Cr(VI) regulation, grade/purity, hydration state, impurity limits, dangerous-goods controls and authorized end use.
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CHEMISTRY, MANUFACTURING CONTEXT & MATERIAL BEHAVIOUR
The chromate/dichromate equilibrium depends strongly on pH: more acidic conditions favor dichromate/polychromate species, while more alkaline conditions favor chromate. Sodium dichromate is therefore both a source of Cr(VI) and a strong oxidizing process reagent. Hydration state is not a cosmetic distinction - it changes formula mass, assay basis and material balance.
PROCESS-ENGINEERING & GRADE-SELECTION CONSIDERATIONS
- Correct identity first: CAS 7775-11-3 belongs to sodium chromate, not sodium dichromate. Do not use it on an Na₂Cr₂O₇ page.
- State hydration form in the RFQ and COA. Anhydrous and dihydrate material cannot share one molar mass or water specification.
- Specify Na₂Cr₂O₇ assay on a clearly defined basis, plus moisture/water of crystallization and relevant Na/Cl/SO₄/insoluble or metal impurity limits according to process.
- Cr(VI) is heavily regulated. In the EU, sodium dichromate is listed in REACH Annex XIV; the buyer must verify whether the intended use is authorized, exempt or prohibited.
- Closed handling, dust control, segregation from reducing/combustible materials and compliant hazardous-waste management are mandatory engineering considerations.
◎ Technical Specifications
| Property | Value |
|---|---|
Formula | Na₂Cr₂O₇ (anhydrous); Na₂Cr₂O₇·2H₂O (dihydrate) |
CAS | 10588-01-9 anhydrous; 7789-12-0 dihydrate |
EC | 234-190-3 (sodium dichromate substance entry) |
Molar mass | 261.97 g/mol anhydrous; 298.00 g/mol dihydrate |
Appearance | Orange to red/orange crystalline solid; grade/form dependent |
Water behaviour | Highly water soluble; forms Cr(VI) chromate/dichromate species depending on pH/concentration |
Functional role | Strong oxidizer and Cr(VI) intermediate |
Regulatory note | EU REACH Annex XIV substance; end-use authorization/exemption status must be verified |
Packaging / transport | Product- and route-specific dangerous-goods packaging; confirm current SDS and shipping classification |
INDUSTRIAL APPLICATION MATRIX
Selected surface-treatment / plating chemistry
- Process role: Oxidizing / passivating chromium source in legacy or specialty processes
- Critical parameters: Process approval; purity; contamination limits; authorization
Sodium chlorate manufacture (selected authorized uses)
- Process role: Process additive for parasitic-reaction / corrosion control in specific systems
- Critical parameters: Exact approved use; concentration; regulatory authorization
Specialty oxidation chemistry
- Process role: Strong inorganic oxidizer
- Critical parameters: Assay; water content; compatibility; waste-treatment plan
QUALITY CONTROL, COA PARAMETERS & TEST FOCUS
Na₂Cr₂O₇ Assay / Cr(VI): Verified through redox titration or validated methods to confirm primary active content and product concentration.
Hydration / Moisture: Evaluated using loss-on-drying or validated methods to ensure material identity, accurate material balance, and proper storage.
Sulfate / Chloride: Measured through ion analysis or producer methods to control process contamination.
Sodium / Metals: Analyzed using ICP or AAS where required to verify product grade and purity.
Water-Insoluble Matter: Determined through gravimetric analysis to ensure solution cleanliness.
Appearance / Caking: Assessed visually to evaluate storage conditions and material quality upon receipt.
STORAGE, HANDLING, MATERIALS COMPATIBILITY & HSE
Sodium dichromate is a high-consequence Cr(VI) chemical. ECHA lists sodium dichromate in REACH Annex XIV for carcinogenic, mutagenic and reproductive-toxicity concerns. Use closed handling where feasible, local exhaust ventilation, exposure monitoring, appropriate respiratory/skin/eye protection, strict segregation and controlled hazardous-waste routes. Never reduce this to a generic 'irritant' statement.
PACKAGING, TRANSPORT & SUPPLY PLANNING FOR GCC / MENA
Use only the packaging configuration approved for the exact supplied form and transport route. Confirm UN certification where required, moisture protection, palletization, dangerous-goods declaration, segregation/stowage requirements, destination restrictions and receiving-site authorization before shipment.
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Frequently Asked Questions
No. That CAS is associated with sodium chromate; sodium dichromate uses 10588-01-9 (anhydrous) and 7789-12-0 (dihydrate).
About 261.97 g/mol for anhydrous Na₂Cr₂O₇ and 298.00 g/mol for the dihydrate.
No. It changes molecular mass, assay basis, water content and process material balance.
Cr(VI) regulatory/HSE compliance and correct chemical identity are as critical as commercial purity.
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