Chemical Reactions

 

 

Metal + Oxygen -> Metal oxide

2Mg  _(s) + O_{2 (g)} -> 2MgO _(s)

                                                             

Metal + Water -> Metal hydroxide + Hydrogen

Mg _(s) + H₂O _(l) -> Mg(OH)_{2 (aq)} + H _{2 (g)}

 

Metal + Acid -> Salt + Hydrogen

Mg _(s) + H₂SO_{4 (aq)} -> MgSO_{4 (aq)} + H _{2 (g)}

 

Base + Acid -> Salt + Water

MgO _(s) + HCl _(aq) -> MgCl_{2 (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.

CaCO_{3 (s)} -> CaO _(s) + CO_{2 (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)} + CO_{2 (g)} -> CaCO_{3 (s)} + H₂O _(l)

 

If you continue to bubble carbon dioxide through limewater the precipitate of CaCO₃ will form a solution of calcium hydrogen carbonate.

CaCO_{3 (s)} + CO_{2 (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