Product Overview
Sodium thiosulfate pentahydrate is an inorganic salt (Na2S2O3·5H2O, CAS 10102-17-7) offered in technical grade. It is a strong reducing agent with high water solubility, making it a workhorse across water treatment and industrial processing. This listing is carried in technical grade — the industrial designation for water-treatment and process work.
Available in sizes from 2 lb bench quantities through 55 lb bags, sodium thiosulfate from Alliance Chemical ships with an SDS, and a lot-specific Certificate of Analysis is available on request, within 1-2 business days.
Why This Grade
Technical grade sodium thiosulfate is the grade most commonly requested for dechlorinating municipal water and photographic processing where residual impurities can interfere with results or downstream product quality.
It is the practical fit for large-scale dechlorination of cooling-tower blowdown and wastewater, photographic fixing and textile antichlor work. If your SOP calls for a certified reagent for standardized titrant preparation, specify a reagent grade — this listing is not supplied to those limits.
Chemical Profile
This product is sodium thiosulfate pentahydrate, Na2S2O3·5H2O, with a molecular weight of 248.18 g/mol (CAS 10102-17-7). It is supplied as colorless to white translucent crystals with a density of 1.69 g/cm³, and it melts in its own water of hydration at about 48 °C. The compound is highly soluble in water but practically insoluble in alcohol — an important handling note for labs using mixed-solvent systems. Vapor pressure at 20 °C is negligible, so no significant off-gassing occurs at ambient storage conditions.
Industrial Applications
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Water Treatment & Dechlorinating— Sodium thiosulfate neutralizes free chlorine and chloramines in municipal discharge, cooling-tower blowdown and aquaculture systems. Operators dose it directly into the effluent stream where it reduces residual chlorine to chloride, bringing discharge into permit limits. It is the ideal dechlorinating agent for many facilities because it reacts quickly and does not introduce problematic byproducts.
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Photographic Processing— Known historically as "hypo" sodium thiosulfate fixes photographic images by dissolving unreacted silver halides from the emulsion. Film and print processors still depend on it wherever silver-halide chemistry is in use.
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Textile Processing— After chlorine-based bleaching, residual chlorine can weaken fibers and cause uneven dye uptake. Sodium thiosulfate is dosed in the rinse bath to neutralize that residual chlorine before the dyeing step.
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Technical Manufacturing— Sodium thiosulfate is used as a process intermediate in the synthesis of certain technical compounds, where its reducing properties drive specific reaction steps.
Handling & Storage
Sodium thiosulfate is not classified as hazardous under GHS based on available data (per the product's GHS classification). No GHS signal word applies. That said, standard chemical-handling practice still governs: wear chemical-splash goggles and nitrile or HDPE gloves when handling dry crystals or preparing solutions. Avoid generating airborne dust.
Store in a cool, dry area away from strong oxidizers and acids, which can decompose thiosulfate to sulfur dioxide. HDPE containers are ideal for long-term storage because they resist moisture transmission. Keep containers sealed — sodium thiosulfate is hygroscopic enough that uncovered product will absorb atmospheric moisture over time, affecting weighing accuracy and technical preparation. Avoid prolonged exposure to heat or direct sunlight.
Hazmat & Shipping
Sodium thiosulfate is not regulated as a hazardous material for transport under DOT/49 CFR. No UN number, hazard class, packing group, or proper shipping name is assigned (per 49 CFR 172.101). This classification simplifies logistics compared to many industrial chemicals, though specific carrier policies and receiver requirements may still apply.
Documentation
An SDS ships with every order and is available in English, Spanish, French and Japanese. A lot-specific Certificate of Analysis (COA) is also available for each shipment, giving buyers the traceability that technical-grade workflows require. A Technical Data Sheet (TDS) is on file for reference.
Why Buy from Alliance Chemical
This sodium thiosulfate is available in sizes from 2 lb bench packs to 55 lb bags — each shipped with an SDS, with a lot-specific COA available on request within 1-2 business days. Alliance Chemical has operated from our Taylor, Texas warehouse since 1998, serving over 55,000 customers across industrial, municipal and technical markets. Shipping and handling guidance on this listing is reviewed by Andre Taki, DOT Hazmat Specialist.
