Write balanced chemical equations for the reactions between<br>i) Sodium thiosulphate and hydrochloric acid<br>ii) Magnesium and steam<br>iii) Calcium and oxygen<br>iv) Bromine and potassium iodide solution<br>v) Zinc and copper sulphate solution.

(i) $$\mathrm{Na_2S_2O_3 + 2HCl \rightarrow 2NaCl + SO_2 + S + H_2O}$$ (a pale yellow precipitate of sulphur forms).<br>(ii) $$\mathrm{Mg + H_2O(g) \rightarrow MgO + H_2}$$<br>(iii) $$\mathrm{2Ca + O_2 \rightarrow 2CaO}$$<br>(iv) $$\mathrm{Br_2 + 2KI \rightarrow 2KBr + I_2}$$ (bromine, being more reactive, displaces iodine and the solution turns brown).<br>(v) $$\mathrm{Zn + CuSO_4 \rightarrow ZnSO_4 + Cu}$$ (zinc displaces copper; the blue colour fades and red-brown copper is deposited).