Question

When $HCl$ reacts with manganese dioxide what does it evolve to be chlorine gas?

Answer 1

For getting the answer for this question we have to study the nature of Manganese oxide and its reaction with acids. We will write the reaction and understand the process behind it to identify the products formed.

Complete answer:
Manganese dioxide is an inorganic compound with chemical formula $Mn{O_2}$ . It is black or brown coloured solid in appearance and occurs in nature in the form of mineral pyrolusite which is the main ore of manganese and a component of manganese nodules. Manganese dioxide is a very strong oxidising agent.
Manganese oxides on reaction with concentrated hydrochloric acid forms manganese chloride water and chlorine gas. The evolved gas is yellow green in colour and it has a pungent smell. We are given manganese dioxide in the question. Let's see its reaction with hydrochloric acid.
$Mn{O_2} + 4HCl \to MnC{l_2} + 2{H_2}O + C{l_2}$
In the above reaction we can see one mole of manganese dioxide reacts with four moles of hydrochloric acid to form one mole of manganese chloride, two moles of water and one mole of Chlorine gas. In this reaction hydrochloric acts as a reducing agent and manganese dioxide acts as an oxidising agent. It oxidises the hydrochloric acid to liberate chlorine gas.

Note:
The main use of manganese dioxide is in making the dry-cell batteries such as alkaline battery and zinc-carbon battery. Manganese is also used in preparation of Potassium permanganate which is also a strong oxidising agent. Manganese oxide is also used in organic synthesis for example it is used for the oxidation of allylic alcohols.