Magnesium Sulfate
Properties
| State | Solid at room temperature |
| Color | White crystalline solid |
| Solubility | Soluble in water (35.1 g/100 mL at 20 °C) |
| Melting Point | 1124 °C (anhydrous) |
About Magnesium Sulfate
Magnesium sulfate's anhydrous form (MgSO4, 120.366 g/mol) and its heptahydrate (Epsom salt, 246.474 g/mol) are the same compound at very different states of hydration, and the chemistry of one is largely defined by how readily it converts to the other. The anhydrous powder, prepared by drying the heptahydrate above 250 °C, is hygroscopic enough to be the standard drying agent for organic chemists: stir 1 to 5 g of MgSO4 into a wet ether or DCM extract, watch the cloudy solution clarify as the salt scoops up trapped water and crumbles into a hydrated mass, then filter through a glass-fritted funnel. It is faster and gentler than Na2SO4, less aggressive than CaCl2, and chemically inert toward almost everything except the most acid-sensitive substrates. In medicine, IV magnesium sulfate at 4 to 5 g loading dose followed by 1 to 2 g/h is the standard-of-care treatment for severe preeclampsia and eclampsia (the MAGPIE trial in 2002 settled this) and is on the WHO Essential Medicines List. Pulmonologists use 2 g over 20 minutes for status asthmaticus that is not responding to beta-agonists. In agriculture, broadcast MgSO4 corrects magnesium-deficient pasture (interveinal chlorosis on older leaves, characteristic 'rabbit-tracks' on sugarcane) without raising soil pH the way dolomitic lime would. Ocean-aquarium hobbyists reach for MgSO4 to top up trace magnesium when carbonate hardness drifts low.
Where you'll encounter it
If you have ever stirred MgSO4 into a separatory-funnel extract before rotovapping, watched an OB nurse hang a 4-g IV bolus for a preeclamptic patient, or dosed a reef tank to bring Mg back into the 1280-1350 ppm window, you have been working with anhydrous or near-anhydrous MgSO4. A synthetic chemist working up a wet ether layer scoops a spatula-tip of MgSO4 into the cloudy phase, watches the powder clump as the salt grabs water in seconds, then filters through cotton — the workhorse dry-down that beats Na2SO4 on speed. An OB team managing a preeclamptic patient runs a 4 g IV load over 20 minutes followed by 2 g/h, with patellar reflex checks every hour because loss of the knee jerk is the early sign that serum Mg is approaching the respiratory-depression threshold. Reef hobbyists dose MgSO4 to lift tank Mg back into the 1280-1350 ppm window.
Common Uses
- Standard drying agent for organic solvents in synthetic laboratories
- IV treatment for severe preeclampsia and eclampsia (4-5 g load, 1-2 g/h maintenance)
- IV bronchodilator for status asthmaticus (2 g over 20 minutes)
- IV antiarrhythmic for torsades de pointes (1-2 g)
- Soil and foliar fertilizer for magnesium-deficient crops
- Reef-aquarium magnesium supplementation
- Bath salt and Epsom salt soak (as the heptahydrate)
Safety Information
Low oral toxicity; gram-scale doses produce predictable osmotic laxation. IV administration must be supervised — too-rapid push or accumulation in renal failure causes loss of patellar reflexes (above 4 mEq/L), respiratory depression (above 10 mEq/L), and cardiac arrest (above 15 mEq/L). The IV antidote is 1 g calcium gluconate over 5 to 10 minutes. Anhydrous powder mildly irritates eyes; standard lab PPE suffices. Not classified hazardous under GHS for non-IV use.
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.