Thin strips of magnesium, copper and iron are taken.

(a) Write down what happens when these metals are treated as follows

(i) Heated in presence of air

(ii) Heated with dil. HCl

(iii) Added to an aqueous solution of zinc sulphate

(b) Arrange these metals in descending order of reactivity.

(a) (i) When we heat magnesium, copper and iron in presence of air they form respective oxides.

(ii) Magnesium and iron react with HCl liberating hydrogen and forming their respective salts.

Mg + 2HCl ⟶ MgCl₂ + H₂ ↑

Fe + 2HCl ⟶ FeCl₂ + H₂ ↑

As Cu is below hydrogen in metal reactivity series, hence, it cannot displace hydrogen from acid and so no reaction takes place.

Cu + HCl (dil) ⟶ no reaction

(iii) Magnesium will displace zinc from zinc sulphate solution as magnesium is more reactive than zinc and is placed above zinc in the reactivity series of metals.

Mg + ZnSO₄ ⟶ MgSO₄ + Zn

Copper and iron are less reactive and are placed below zinc in the reactivity series, hence will not displace it and no reaction will take place.

(b) Mg > Fe > Cu