(a) What is reactivity series? How does the reactivity series of metals help in predicting the relative activities of various metals?
(b) Suggest different chemical processes used for obtaining a metal from its oxides for metals in the middle of the reactivity series and metals towards the top of the reactivity series. Support your answer with one example each.
(a) Reactivity Series: The reactivity series is a list of metals arranged in the vertical column in order of their decreasing activities.
Reactivity Series help in predicting the relative activities of various metals. For example- A metal placed above hydrogen in the activity series will displace hydrogen from water or acids. A metal which is at the top of the reactivity series would displace metals below it. Therefore, a more reactive metal displaces a less reactive metal from its salt solution.
(b)
(i) The metals in the middle of the activity series such as iron, zinc etc. are moderately reactive, and usually present as sulphides or carbonates in nature. The sulphide ores and carbonate ores are converted into oxides by roasting and calcination respectively. The metal oxides are then reduced to corresponding metals by using suitable reducing agent such as carbon (coke).
Example: 2Fe2O2 + 3C → 4Fe + 3CO2
ZnO + C → Zn + CO
(ii) The metals high up in the reactivity series are very reactive. They cannot be obtained because these metals have high affinity for oxygen than carbon. Therefore, these metals are obtained by electrolytic reduction.
Example: Electrolysis of sodium chloride (Nacl).
- At cathode: Na + e- → Na
- At anode: 2Cl → Cl2 + 2e-