Question

Sodium amalgam is used as:
(a) oxidising agent
(b) catalyst
(c) reducing agent
(d) bleaching agent

Answer 1

Hint: Amalgam is a mixture of a metal with another fixed metal Mercury. It can be naturally occurring or man-made. Sodium amalgam is the mixture of Sodium metal with Mercury.

Complete step by step answer:
(1) Sodium is the 11th element of the periodic table in the category of alkali metals with atomic number 11. It is very volatile in a free state. It can catch fire if kept open in air or react violently with water. That’s why it is kept in kerosine or some liquid solution. Since, Sodium is very unstable, it always occurs as a combined form in nature. Here, it is combined with Mercury to form a substance called amalgam. The chemical formula of Sodium amalgam is ${\text{HgNa}}$. So, both the metals are in elemental state, and we know that the oxidation number in elemental state is 0.

(2) For option (a) oxidising agent, oxidation is loss of electron, and the substance which oxides others by reducing themselves are called oxidising agents. Sodium amalgam, ${\text{HgNa}}$ cannot act as an oxidising agent because it cannot gain electron.

(3) For option (b) catalyst, it is a substance which accelerates or decelerates a reaction rate. ${\text{HgNa}}$ does not have any such property, so it cannot act as a catalyst.

(4) For option (c) reducing agent, reduction is gain of electron, and the substance which reduces the other substance by getting itself oxidised is called a reducing agent. The oxidation state of Sodium, and Mercury in Sodium amalgam is zero, so it can lose electrons to have higher positive oxidation number, and higher oxidation means more stability. Therefore, it can be a reducing agent. Hence, this is a correct option, and, so, option (d) is also eliminated.

Hence, option (c) reducing agent is the correct answer.

Note:
In the Chlor Alkali process, which is processed to produce Sodium hydroxide, and Chlorine through the electrolysis of Sodium Chloride solution, Sodium amalgam is obtained as the by-product of it.