Question

You are given samples of three metals-sodium, magnesium and copper. Suggest any two activities to arrange them in order of their decreasing reactivities.

Answer 1

Hint: The reactivity of a metal depends mostly on their Electronic configuration and the tendency to lose the electron. We arrange the metals in the order of their decreasing reactivity in a series called activity or reactivity series. More reactive elements have a great tendency to lose electrons. In the question we are given 3 metals- sodium, magnesium and copper so in order to decide its reactivity we perform some reactions.

Complete answer:
We will observe 2 such reactions to decide the reactivity order-
1. Reaction with Oxygen (air)-
Sodium belongs to the first group of the periodic table (alkali family) and is highly reactive in nature. Sodium can easily lose electrons to attain noble gas configuration. Sodium reacts vigorously in air or oxygen and forms sodium oxide.
 $ 2Na + {O_2} \to 2N{a_2}O $
Magnesium belongs to the second group of periodic table (Alkaline earth metals). Magnesium reacts with oxygen only on heating to give Magnesium oxide.
 $ 2Mg + {O_2}\xrightarrow{{heat}}2MgO $
Copper belongs to the d block or the transition metal series. Copper does not react with oxygen at all and only reacts on prolonged heating.
 $ Cu + {O_2} \to $ No reaction
This Activity proves that the decreasing order of reactivity would be-
Sodium>Magnesium>Copper
2. Reaction with water-
Sodium reacts vigorously even with cold water to form Sodium hydroxide.
 $ 2Na + 2{H_2}O \to 2NaOH + {H_2} $
Magnesium reacts with only hot water and produces Magnesium hydroxide.
 $ Mg + 2{H_2}O \to Mg{(OH)_2} + {H_2} $
Copper however does not even react with steam.
 $ Cu + {H_2}O \to $ No reaction
This Activity proves that the decreasing order of reactivity is as follows-
Sodium>Magnesium>Copper
We can consider the example of displacement reactions to prove the reactivity-
Magnesium reacts with Copper sulphate to produce Magnesium sulphate and Copper however the replacement of Magnesium in Magnesium sulphate by copper is not possible since it is highly unreactive.
 $ Mg + CuS{O_4} \to MgS{O_4} + Cu $
 $ Cu + MgS{O_4} \to $ No reaction.

Note:
The high reactivity of sodium is understood from the fact that it is kept immersed in kerosene as under normal conditions it reacts easily with oxygen, carbon dioxide and moisture to even catch fire. However it remains inert in Kerosene oil. This is a useful method to prevent any kind of injuries and accidents in chemical laboratories.