Magnesium chloride (\(\text{MgCl}_2\)) is a salt commonly used in applications ranging from de-icing roads to dietary supplements. It typically appears as a white crystalline solid or is dissolved in brine solutions. Magnesium chloride is not flammable and will not burn. Understanding why this common substance is fireproof involves looking closely at its chemical structure and stability.
The Direct Answer: Chemical Stability
Magnesium chloride is classified as non-combustible and non-flammable. This stability stems from its nature as an ionic compound, formed by the strong electrostatic attraction between the positively charged magnesium ion (\(\text{Mg}^{2+}\)) and the negatively charged chloride ions (\(\text{Cl}^{-}\)). Ionic bonds are exceptionally strong, requiring a massive input of energy to break, which prevents the rapid chemical reaction necessary for combustion.
Flammability requires a substance to be easily oxidized or to produce volatile, ignitable vapors, criteria magnesium chloride does not meet. While the compound is stable, extreme heating above \(700^{\circ}\text{C}\) can cause it to decompose. This decomposition is not combustion and slowly releases toxic byproducts such as hydrogen chloride and chlorine gas.
Distinguishing Salt from Metal
The confusion regarding flammability often arises from misunderstanding the difference between the compound, magnesium chloride (\(\text{MgCl}_2\)), and its elemental component, pure magnesium metal (\(\text{Mg}\)). Elemental magnesium is highly reactive and extremely flammable. When ignited, magnesium metal burns vigorously with intense heat, a property utilized in flares, fireworks, and flash photography.
The combustion of magnesium metal is an exothermic oxidation reaction where the metal readily reacts with oxygen. This reaction is so intense that standard fire extinguishers, including water and carbon dioxide, are ineffective and can even worsen the fire. Magnesium chloride, the salt, has already completed this oxidation process, existing in a chemically stable, non-reactive state.
Alternative Safety Considerations
While magnesium chloride poses no fire hazard, other safety considerations are necessary for proper handling and storage. The substance is classified as an irritant because it can cause discomfort upon contact with the body. Direct exposure to the solid or concentrated solutions can lead to irritation of the skin, eyes, and respiratory tract, particularly if dust is inhaled.
Proper storage is important because magnesium chloride is highly hygroscopic, meaning it readily absorbs moisture from the air. If not stored in a cool, dry, and tightly sealed container, it will absorb water and dissolve into a liquid brine solution. This absorption of moisture can reduce its effectiveness and may lead to caking or corrosion of metal containers.