SODIUM MOLYBDATE DIHYDRATE

Sodium molybdate dihydrate (Na₂MoO₄·2H₂O) is the hydrated form of sodium molybdate — a white, water-soluble crystalline salt of molybdenum in oxidation state +6 associated with the molybdate anion MoO₄²⁻. 
It is widely used as a source of molybdenum in catalysts, fertilizers and animal feeds, as a corrosion inhibitor, and in analytical chemistry. 
This article reviews the chemistry, physical properties, crystal structure, analytical methods, synthesis and industrial manufacture, major applications, environmental and toxicological aspects, handling and storage, and alternatives and derivatives. 
Key physical constants, typical preparation routes and safety considerations are provided.
CAS number: 10102-40-6. 
Other names / synonyms: disodium molybdate dihydrate; molybdic acid sodium salt dihydrate; sodium molybdate·2H₂O; sodium molybdate (dihydrate).
Molecular and crystal structure
 
Sodium molybdate contains the tetrahedral molybdate anion MoO₄²⁻. In the dihydrate form, two water molecules are coordinated in the crystal lattice and participate in hydrogen bonding with the oxyanions and sodium cations, producing a layered crystal structure. 
The dihydrate has been characterized crystallographically: reported unit cell parameters and space group (often cited as orthorhombic, Pbca, with cell constants on the order of a = 8.46 Å, b = 10.55 Å, c = 13.83 Å in early structural studies) show alternating layers of MoO₄ tetrahedra and water molecules connected by sodium ions and hydrogen bonds. 
These structural features influence hydration behavior, dehydration temperatures, and solid-state reactivity. 
 
Physical properties
Density: reported values vary with hydration and packing; typical solid densities for related sodium molybdate solids are around 3.2–3.8 g·cm⁻³ depending on hydration state and measurement method. 
Melting / decomposition: decomposes on strong heating; reported high temperature (decomposition/melting around several hundred °C; anhydrous Na₂MoO₄ has a high melting/decomposition point). 
Many vendor notes list “decomposes” rather than a sharp melt for the dihydrate. 
Solubility: readily soluble in water; solubility increases with temperature. 
Published solubility data and vendor sheets indicate good aqueous solubility (e.g., substantial grams per 100 mL at elevated temperature). 
Exact solubility tables should be consulted when precise concentrations are needed for synthesis or formulation. 
Appearance / odor: white, odorless crystalline powder. 
 
Chemical behavior and reactivity
Acid–base behaviour: the molybdate anion behaves as the conjugate base of molybdic acid (H₂MoO₄). 
In aqueous solution, molybdate speciation depends strongly on pH, concentration and presence of complexing cations: at high pH the simple MoO₄²⁻ species predominates; at lower pH polymeric polymolybdate species (e.g., Mo₇O₂₄⁶⁻) can form. 
This speciation controls redox chemistry, complexation with metals, precipitation behavior and catalytic properties. 
Redox chemistry: molybdenum(VI) in MoO₄²⁻ can be reduced to lower oxidation states (e.g., Mo(V), Mo(IV)) under strongly reducing conditions; such redox changes are central to analytical reactions (e.g., the formation of molybdenum blue) and catalytic redox cycles. 
Complexation and ligand behavior: molybdate forms coordination complexes with transition metals (e.g., ammonium or transition-metal molybdates, heteropoly acids), and with organic ligands in certain media; molybdate also interacts with phosphate/arsenate chemically and can form mixed anions or competitive adsorption in soils. 
 
Analytical identification and characterization
Spectroscopic and diffraction methods
X-ray crystallography provides definitive unit cell and atomic arrangement (see structural studies cited). 
FTIR / Raman: characteristic Mo–O stretching bands (typical tetrahedral MoO₄²⁻ vibrational signatures) appear in the IR/Raman spectra; hydration shows O–H stretching bands.
UV-Vis (molybdenum blue): under reducing acid conditions, molybdate forms reduced complexes that show intense blue color (basis of classic quantitative spectrophotometric methods for trace molybdenum and phosphate in the presence of vanadium or after reduction).
XRF / ICP-OES / ICP-MS: elemental molybdenum and sodium are quantifiable by these techniques; ICP methods are used for trace-level determination and purity assays.
Thermogravimetric analysis (TGA): used to determine water of hydration (mass loss corresponding to two H₂O per formula unit) and identify dehydration/decomposition temperatures.
Wet chemical tests
Precipitation and oxidation–reduction color tests are classical for molybdates: formation of molybdenum blue upon reduction is diagnostic. Standardized methods exist for environmental and soil analyses.

SAFETY INFORMATION ABOUT SODIUM MOLYBDATE DIHYDRATE

 
 
 
 
 
First aid measures:
Description of first aid measures:
General advice:
Consult a physician. 
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
 
If inhaled:
If breathed in, move person into fresh air. 
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately. 
Wash off with soap and plenty of water.
Consult a physician.
 
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
 
If swallowed:
Do NOT induce vomiting. 
Never give anything by mouth to an unconscious person. 
Rinse mouth with water. 
Consult a physician.
 
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
 
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment. 
 
Avoid breathing vapours, mist or gas. 
Evacuate personnel to safe areas.
 
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste. 
Keep in suitable, closed containers for disposal.
 
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
 
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place. 
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
 
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
 
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles. 
Faceshield (8-inch minimum). 
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
 
Skin protection:
Handle with gloves. 
Gloves must be inspected prior to use. 
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product. 
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. 
Wash and dry hands.
 
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
 
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls. 
 
If the respirator is the sole means of protection, use a full-face supplied air respirator. 
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so. 
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions. 
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
 
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company. 
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product