Sodium Silicate (Water Glass): Formula, Ratio, Grades, Uses and Safe Handling

Sodium silicate formula and names

Sodium silicate is not a single compound but a family made from sodium oxide (Na₂O) and silica (SiO₂), with the general formula Na₂O·nSiO₂, where n is the ratio of silica to sodium oxide. The simplest member, sodium metasilicate, has a 1:1 molar ratio and the formula Na₂SiO₃. The solutions sold as liquid sodium silicate, or water glass, contain more silica: HSDB gives molar ratios of 1.5 to 3.3 for commercial grades.

The molar mass of Na₂SiO₃ is 2 × 22.990 (sodium) + 28.085 (silicon) + 3 × 15.999 (oxygen) = 122.06 g/mol, or about 50.8% Na₂O and 49.2% SiO₂ by mass. Confirm your national tariff line with your customs broker.

Weight ratio and molar ratio

Specifications quote the ratio either by weight or by moles. Because one mole of Na₂O (61.98 g) weighs slightly more than one mole of SiO₂ (60.08 g), the molar ratio is about 1.032 times the weight ratio: a weight ratio of 3.22 is a molar ratio of about 3.32. According to HSDB, the higher the ratio, the less sodium the product contains and the lower its solubility and alkalinity.

Appearance and properties

Sodium silicate is sold as glassy lumps, powder or granules, and most often as a solution: the International Chemical Safety Card (ICSC 1137) describes the common liquid as a colourless 25–50% solution in water.

Values are from ICSC 1137, NOAA’s CAMEO Chemicals database and HSDB. Two reactions explain many of its uses: acidified solutions form silica gel (HSDB notes that gels form between pH 3 and 9), and silicate is precipitated by calcium, magnesium and heavy-metal ions.

Grades: ratio, Baumé and solids

HSDB notes that grades differ in concentration, specific gravity and viscosity, and that a 40% solution is commonly used. A grade is defined by a handful of figures, which should all appear on the Certificate of Analysis (CoA): the SiO₂:Na₂O ratio, by weight or by moles; the Na₂O and SiO₂ percentages, which together give the total solids; the density, as specific gravity or degrees Baumé; the viscosity; and, where colour or purity matters, iron and insoluble matter.

What 41 °Bé means

Liquid grades are often sold by Baumé, a density scale for liquids heavier than water. On the US scale, specific gravity = 145 ÷ (145 − °Bé), so a 41 °Bé grade has a specific gravity of about 1.39, in line with the ICSC’s figure of 1.4. Baumé gives the density, not the ratio, so specify both.

How sodium silicate is made

HSDB describes the main route: silica sand is fused with soda ash (sodium carbonate) in a furnace, and carbon dioxide is driven off.

Na₂CO₃ + nSiO₂ → Na₂O·nSiO₂ + CO₂

The proportion of sand to soda ash sets the ratio. The glass is then dissolved in water under steam pressure to give liquid sodium silicate. Our guide to sodium carbonate (soda ash) covers the main sodium raw material.

What sodium silicate is used for

Reference sources summarised in PubChem and Haz-Map, including HSDB, the Merck Index, Ullmann’s and the OECD, list these main uses:

• Detergents and cleaners: to soften water and boost cleaning, in laundry, dairy, floor and metal cleaners. Sodium metasilicate goes into heavy-duty alkaline products.
• Silica, silica gel and zeolites: acidifying sodium silicate gives silica gel, and it is a starting material for precipitated silicas, zeolites and silica catalysts.
• Pulp, paper and textiles: as a bleaching aid and bleach stabiliser, in sizing, and in deinking recycled paper.
• Adhesives and binders: for sealing and laminating paperboard containers, and as a binder in ceramics, refractories, welding rods, foundry moulds and cores, and grinding wheels.
• Construction: waterproofing mortars and cements, penetrating sealants, soil stabilisation, and spray coatings for tunnels and mines.
• Water treatment: as a corrosion inhibitor, in boiler compounds and as a flocculant. US FDA rules (21 CFR 173.310) allow sodium silicate and sodium metasilicate as boiler water additives where steam contacts food.
• Oil, gas and mining: in drilling fluids, enhanced oil recovery and ore treatment.
• Other uses: fireproofing wood, paper and fabric; masonry and glass paints; titanium dioxide production; and as a shell coating to preserve eggs.

FDA also lists sodium silicate as an anticaking agent, drying agent, humectant and processing aid in food. Food and boiler uses need a suitable grade and documents, so state the end use when you enquire.

Hazards, storage and transport

The main hazard of sodium silicate is its alkalinity, which can corrode metal and injure skin and eyes (Ullmann, as summarised by Haz-Map). How hazardous a product is depends on its ratio and concentration.

• Sodium metasilicate: its EU harmonised classification is skin corrosion category 1B (H314, causes severe skin burns and eye damage) and STOT SE 3 (H335, may cause respiratory irritation).
• Sodium silicate (CAS 1344-09-8): classifications notified to the European Chemicals Agency vary with the grade. The most common are skin irritation (H315), serious eye damage (H318) and respiratory irritation (H335); about a fifth of reports give skin corrosion (H314).
• Eyes: HSDB reports that splashes damaged the cornea even when washed off promptly, so always wear eye protection.
• Metals: solutions react with aluminium and zinc and release flammable hydrogen, so keep them out of aluminium and galvanised containers.

The ICSC lists cough, sore throat, redness and pain of the skin and eyes, and nausea and vomiting if swallowed, and advises ventilation, gloves and a face shield. For first aid, rinse skin with plenty of water for at least 15 minutes; rinse eyes for several minutes and get medical attention; if swallowed, rinse the mouth, give one or two glasses of water and do not induce vomiting. Store sodium silicate separated from strong acids, aluminium and zinc, and keep containers closed, because the solid absorbs moisture.

Transport classification also depends on the form and grade:

Check section 14 of the current SDS for the exact grade, and confirm packing and labels with your freight forwarder.

Questions to ask a supplier

• Is the ratio quoted by weight or by moles, and what are the Na₂O, SiO₂ and total solids figures?
• What is the density in °Bé or specific gravity, at what temperature, and what is the viscosity?
• What are the limits for iron and insoluble matter, if colour or clarity matters for your use?
• Can you share a recent Certificate of Analysis and the current SDS, including the transport details in section 14?
• What packing do you offer, for example drums or IBCs, and is it free of aluminium and zinc?

Enquire with Scapex Exports

Scapex Exports is an exporter and supplier of industrial and specialty chemicals from India. Our sodium silicate liquid page lists the standard grade and packing and links to its COA and MSDS. Related products include sodium metasilicate pentahydrate, potassium silicate solution, soda ash dense, caustic soda flakes and quartz silica powder.

Tell us the ratio, density or solids content you need, the quantity, packing and destination port, and we will reply with a quotation.

Frequently asked questions

Sources: ILO/WHO International Chemical Safety Card ICSC 1137, sodium silicate (solution 25–50%); NOAA CAMEO Chemicals datasheet for sodium silicate; HSDB, Haz-Map, ECHA and EU CLP records for sodium silicate via PubChem; US Code of Federal Regulations, 21 CFR 173.310; US Harmonized Tariff Schedule, heading 2839.