Sodium Sulfate
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Soluble in water (195 g/L at 20 °C; solubility peaks at 49.7 g/100 mL at 32.4 °C) |
| Melting Point | 884 °C |
| Boiling Point | 1429 °C |
About Sodium Sulfate
Anhydrous sodium sulfate (Na2SO4, 142.04 g/mol) is the white powder you reach for in an organic synthesis lab when you need to dry an organic extract before rotary evaporation — pour it onto a wet ether or DCM layer in a separatory funnel, swirl, watch the suspended water turn the powder slightly clumpy, then filter. It absorbs water by converting back to the decahydrate (Glauber's salt), with a theoretical capacity of about 1.27 g of water per gram of anhydrous salt. Industrially, sodium sulfate is one of the highest-tonnage inorganic chemicals on earth — global production is roughly 6 million tonnes per year. About half of that is captured as a by-product of viscose rayon manufacturing and chromate production; the rest is mined as the natural mineral thenardite or recovered from brine lakes. The biggest single end-use is powdered laundry detergent, where Na2SO4 functions as an inexpensive flow agent and filler at 20 to 70% of the formulation by weight (it bulks the box, prevents caking, and helps the surfactants dissolve cleanly in the wash water). Kraft paper mills consume the second-largest fraction as 'salt cake' that is reduced in the recovery boiler to Na2S for the white-liquor pulping cycle. Glass batches use small amounts as a fining agent to clear bubbles from molten soda-lime glass.
Where you'll encounter it
If you have ever extracted caffeine from tea, run a Grignard, or done a Steglich esterification, the white powder you sprinkled into the organic layer to dry it before solvent removal was anhydrous sodium sulfate. It is the universal first-pass drying agent in synthetic organic chemistry — cheap, neutral pH, doesn't react with most functional groups, plays nicely with esters, ethers, ketones, and aromatic amines. The competing options each have downsides: MgSO4 has higher capacity but is mildly acidic and can isomerize sensitive enol ethers; CaSO4 has the highest efficiency but the smallest capacity; molecular sieves are expensive. In a kraft pulp mill, you encounter Na2SO4 in 20-tonne dump trucks pulling up to the salt-cake silo — the recovery boiler reduces it with carbon to Na2S, which combines with NaOH to make the white liquor that dissolves lignin from wood chips at the next pulping cycle.
Common Uses
- Drying agent for organic extracts in synthetic chemistry workups, capacity ~1.27 g water per gram
- Flow-aid filler in powdered laundry detergent at 20 to 70% of formulation
- Kraft pulping salt cake reduced to Na2S in the chemical recovery boiler
- Glass-batch fining agent at 0.5 to 1.0% to clear bubbles from molten soda-lime glass
- Textile dyeing leveling agent for cotton with reactive and direct dyes
- Carpet-cleaning powder filler and pH-buffering agent
- Tanning industry depilation neutralizer after lime-sulfide hide processing
- Heat-storage medium in molten-salt thermal systems via the decahydrate phase change at 32.4 °C
Safety Information
Low toxicity. GHS: not classified as hazardous. No OSHA PEL for sodium sulfate; OSHA particulates not otherwise regulated apply (15 mg/m3 total dust, 5 mg/m3 respirable). Ingestion of large quantities causes osmotic diarrhea — the basis for the laxative use of the decahydrate. The acute oral LD50 in rats is approximately 5 g/kg, putting it well below the threshold for any GHS acute-toxicity classification. Skin and eye irritation are limited to dust exposure; standard nuisance-dust PPE (safety glasses, dust mask) is adequate. Compatible with most laboratory and industrial materials. Anhydrous Na2SO4 is hygroscopic — store in sealed containers to prevent absorption of atmospheric moisture and conversion to the decahydrate.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.