Question

Which of the following reacts with cold water vigorously?
(A) Carbon
(B) Sodium
(C) Magnesium
(D) Sulphur

Answer 1

Hint: The element reacts vigorously with water if they could exist in a stable state when it is ionized. Even though the water is covalent compound here let’s consider water in ionic form i.e. ${{H}^{+}}, O{{H}^{-}}$

Complete answer:
- If in the question it is asked which of the following elements will react vigorously with water and we have to comment on the reason behind the reaction with water.
- We all are familiar with the options given, here we are asked to comment on the reaction with water and we know that the water is a covalent compound but to solve this question let’s take the water represented in the ionic form i.e. ${{H}^{+}}, O{{H}^{-}}$
- An element reacting with water means it is getting ionized in the presence of water and the reaction will be vigorous if the element could easily ionize and reduce the hydrogen ion to hydrogen.
- So an ion which has a high tendency to lose its valence electrons easily and to form the stable configuration will react vigorously.
- And now compare the options and find out the element which has the highest tendency to oxidize i.e. to lose electrons and exists as a stable ion.
- The first option given is C, it has a valency of four and only shares its electrons and it does not possess the tendency to get oxidized.
Now let’s consider Sodium, here sodium readily gets ionized since the sodium ion is formed by losing one electron and attains the stable gas configuration of He. The sodium ion $N{{a}^{+}}$ ion is more stable than the Na metal.
- The third option is Mg, it also has the tendency to get oxidized but it's less than the Na metal.
- The Sulphur requires 2 more electrons to complete its octet configuration and it has the tendency to gain electrons than losing the electrons.
So by comparing the options, we could say that the sodium has the highest tendency to lose electrons and reduce the \[{{H}^{+}}\] ions in the water to H.
- So we may say that the reaction of Na with water is a redox reaction in which the water is getting reduced and the Na is getting oxidized.
$Na+{{H}^{+}}\to N{{a}^{+}}+H$
The sodium on reaction with water gives sodium hydroxide and hydrogen.
$2Na+2{{H}_{2}}O\to 2NaOH+{{H}_{2}}$

Hence, the correct option is “B”.

Note:
> We have studied that the sodium is kept immersed in kerosene, since if it comes in contact with water then it catches fire and the reaction is explosive.
> During the reaction between Na and water NaOH is formed and the reaction is exothermic and it burns the hydrogen gas formed. Hence, we could see a dancing flame of H above the surface of Na if it comes in contact with water.