Chemical Reactions

Metal + Oxygen Metal oxide
2Mg (s) + O2 (g) 2MgO (s)

Metal + Water Metal hydroxide + Hydrogen
Mg (s) + H2O (l) Mg(OH)2 (aq) + H2 (g)

Metal + Acid Salt + Hydrogen
Mg (s) + H2SO4 (aq) MgSO4 (aq) + H2 (g)

Base + Acid Salt + Water
MgO (s) + HCl (aq) MgCl2 (aq) + H2O (l)

Metal Carbonate + Acid Salt + Water + Carbon dioxide
MgCO3 + HCl MgCl2 +H2O + CO2


Reaction Uses and Observations

In a reaction between a metal and water there would be bubbles/fizzing and the metal would disappear to form a colourless solution – the metal hydroxide formed would have a PH of 9-12 (weak alkali).

Magnesium reacts with oxygen with a bright white flame to form MgO. This is used in indigestion tablets because it’s an alkali and reacts in a neutralisation reaction with HCl to produce water and MgCl2.

Compounds of Calcium

Thermal decomposition of calcium carbonate (limestone) in a limekiln forms calcium oxide (quicklime) and carbon dioxide.
CaCO3 (s) CaO (s) + CO2 (g)

Calcium oxide is used to neutralise acidic soils. It will react with water to form calcium hydroxide (slaked lime) if excess water is used it will form limewater.
CaO (s) + H2O (l) Ca(OH)2 (s or aq)

Ca(OH)2 (s) slaked lime
Ca(OH)2 (aq) limewater

Carbon dioxide will turn limewater milky (a precipitate of calcium carbonate).
Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O (l)

If you continue to bubble carbon dioxide through limewater the precipitate of CaCO3 will form a solution of calcium hydrogen carbonate.
CaCO3 (s) + CO2 (g) + H2O (l) Ca(HCO3)2 (aq)

Calcium hydrogen carbonate is present in ‘temporary hard water’ (tap water) and when heated in the kettle a thermal decomposition reaction occurs to form calcium carbonate (limescale).
Ca(HCO3)2 CaCO3 + CO2 + H2O