Magnesium

Chemical reactions

Reaction of magnesium with acids


Magnesium metal dissolves readily in acids, even weak ones, forming Mg(II) ions and hydrogen, H2 [6].

Mg(s) + H2SO4(aq) Mg2+(aq) + SO42−(aq) + H2(g)
Mg(s) + 2 HCl(aq) Mg2+(aq) + 2 Cl−(aq) + H2(g)
Mg(s) + H2CO3(aq) Mg2+(aq) + CO32−(aq) + H2(g)


Reaction of magnesium with air


Magnesium react with oxygen at room temperature, forming a passivating layer of MgO on the surface. When ingited, Mg reacts with both oxygen and nitrogen forming a mixture of magnesium oxide, MgO, and magnesium nitride, Mg3N2 [6].

2 Mg(s) + O2(g) 2 MgO(s)
3 Mg(s) + N2(g) Mg3N2(s)


Reaction of magnesium with bases


Mg(II) is precipitated by hydroxide ions. Ammonia will also precipitate Mg(II) as hydroxide, but the precipitation is incomplete

Mg2+(aq) + 2 OH−(aq) Mg(OH)2(s)


Reaction of magnesium with carbon dioxide


Magnesium will react with cabon dioxide, when heated, forming magnesium oxide and elemental carbon [6]:

2 Mg(s) + CO2(g) 2 MgO(s) + C(s)


Reaction of magnesium with carbonates


Mg(II) is precipitated by carbonate ions as an alkaline carbonate.

Mg2+(aq) + CO32−(aq) MgCO3(s)


Reaction of magnesium with halogens


Magnesium react with Cl2 forming magnesium chloride [6].

Mg(s) + Cl2(g) MgCl2(s)


Reaction of magnesium with phosphates


Mg(II) is not precipitated by phosphate ions under acetic acid conditions. Under neutral conditions it is precipitated as the hydrogen phosphate

Mg2+(aq) + HPO42−(aq) MgHPO4 · 7 H2O(s)

In the presence of ammonia, an ammonium phosphate is precipitated

Mg2+(aq) + NH3(aq) + HPO42−(aq) MgNH4PO4(s)


Reaction of magnesium with sulfides


Mg(II) is not precipitated by hydrogen sulfide. A precipitate can sometimes be observed due to the alkaline properties of hydrogen sulfide

S2−(aq) + H2O(l) HS−(aq) + OH−(aq)
Mg2+(aq) + 2 OH−(aq) Mg(OH)2(s)


Reaction of magnesium with water


Magnesium does not react with liquid water at room temperature. It does however react with steam, forming magnesium oxide, MgO, or magnesium hydroxide, Mg(OH)2, with excess steam, and hydrogen gas (H2).

Mg(s) + H2O(g) MgO(aq) + H2(g)
Mg(s) + 2 H2O(g) Mg(OH)2(aq) + H2(g)


Quantitative analysis


Method 3500-Mg C Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.01 mg/L
Method limit of detection in soil = 100.0 mg/kg