Question

Which gas is released when dilute sulphuric acid is added to $N{a_2}S$?

Answer 1

In this reaction, two compounds of sulfur with different oxidation numbers react together, thus this is a double displacement reaction.The double displacement reaction is a chemical process which involves the exchange of bonds between the two non-reacting chemical species that results in the formation of products with similar or identical bonding occurring between them.

Complete step by step answer:
Sulphuric acid is a mineral acid which is composed of the sulphur, oxygen and hydrogen elements. It has a chemical formula of ${H_2}S{O_4}$. It is a colorless, odourless and viscous liquid. It is soluble in water and is synthesized in reactions which are highly exothermic in nature. It is widely used in the manufacture of fertilizers and chemicals.
Sodium sulphide is an ionic chemical compound with the chemical formula of $N{a_2}S$. Both its anhydrous and the hydrated salts are colorless solids. It is also soluble in water and gives strongly alkaline solutions. It is a reducing agent.
Now, when dilute sulphuric acid $\left( {{H_2}S{O_4}} \right)$ is added to the sodium sulphide $\left( {N{a_2}S} \right)$ then double displacement reaction takes place. This reaction can be written as $N{a_2}S\left( s \right)\left[ \begin{gathered} sodium \\\ sulphide \\\ \end{gathered} \right] + {H_2}S{O_4}\left( l \right)\left[ \begin{gathered} sulphuric \\\ acid \\\ \end{gathered} \right] \to N{a_2}S{O_4}\left( s \right)\left[ \begin{gathered} sodium \\\ sulphate \\\ \end{gathered} \right] + {H_2}S\left( g \right)\left[ \begin{gathered} hydrogen \\\ sulphide \\\ \end{gathered} \right]$
The products of this reaction are sodium sulphate, which is a salt, and hydrogen sulphide $\left( {{H_2}S} \right)$ which is a gas. This gas is recognized by its rotten egg-like smell.

Hence, the answer is ${H_2}S$ (hydrogen sulphide) gas..

Note: Hydrogen sulphide gas can also be obtained from natural gas. It can even be produced by treating hydrogen with molten elemental sulphur. In this process hydrocarbons are the main source of hydrogen. Moreover, many metal and non metal sulphides such as aluminium sulphide, phosphorus pentasulphide can liberate Hydrogen sulphide gas when they get exposed to water. Hydrogen sulphide gas can also be produced by heating sulfur with solid organic compounds and followed by reduction using hydrogen gas.

The hydrogen sulphide $\left( {{H_2}S} \right)$ gas is poisonous, corrosive and flammable. It is slightly denser than air. ${H_2}S$ burns in oxygen with a blue flame to form sulphur dioxide and water. It acts as a weak acid and as a reducing agent.