Question

What is ‘Tailing of Mercury’?

Answer 1

Hint: Mercury is a liquid metal having an atomic number of $80$, a heavy silvery-white metal that is liquid at ordinary temperatures. It is used in thermometers. Tailing of mercury involves passing ozone through it.

Complete step-by-step answer:
When ozone is passed through mercury, it loses its meniscus and sticks to the glass due to the formation of the mercurous oxide. This is called the tailing of mercury. The meniscus can be restored by shaking it with water.
Simply, Tailing of mercury is defined as sticking of mercury to the sides of the test tube (or any other glassware in which mercury is taken, mainly thermometers) on passing ozone through it. As the following reaction takes place between the nascent oxygen from ozone and mercury.
$O_3+2Hg\to {Hg}_{2}O{+O}_2$
The formation of mercurous oxide ${Hg}_{2}O$ is the cause of sticking.
This can be removed by washing with water, as ${Hg}_{2}O$ is soluble in water.
On-air exposure of the Tailing of mercury signifies a change in the oxidation number by one.

Additional Information:
-In this reaction, the oxidation number of mercury changes from $0$ to $+1$. Thus, it is oxidized.
-The oxidation number of oxygen changes from $0$ to $-2$. Thus, it is reduced. Hence, the tailing of mercury is an intermolecular redox change.
-It is its innate property. It can be removed by adding some impurities like some other metal.

Note: The possibility to make a mistake is that when ozone reacts with mercury then mercurous oxide ${Hg}_{2}O$ will be formed, not mercury(II) oxide $HgO$.