Question

What will happen after action of dilute hydrochloric acid on sodium sulphide?

Answer 1

Hint:
- The reaction of dilute strong acid along with alkali metal sulphide results in the formation of salt and evolution of the sulphide gas.
- The chemical equation expressing a reaction between two reactants, should always be balanced, by adding the required coefficients.

Complete answer:
> Hydrochloric acid is a strong acid which tends to dissociate completely into its constituent ions in a solution. This can be chemically represented as an equation, which is given below $HCl\rightleftharpoons {{H}^{+}}+C{{l}^{-}}$
> Here, as we can see the hydrochloric acid is dissociated into a proton and chloride ion. The liberation of this proton makes it an acid, by the definition of acids, which is, the species which liberate protons in a solution are termed as acids. Similarly, the species which liberate hydroxide ions in a solution are termed as bases. Now, if we consider the question, it is being mentioned that the acid is dilute, which means it has some content of water in it. So, the proton would exist as hydronium ion in the solution. It has a chemical formula ${{H}_{3}}{{O}^{+}}$.
> Now, considering the other reactant which is sodium sulphide. It has the chemical formula $N{{a}_{2}}S$, as we can see, it contains two atoms of sodium metal and one atom of sulphur, combined with each other to form sodium sulphide. Now, if we look at this molecule ionically, it is made up of $N{{a}^{+}}$ and ${{S}^{2-}}$.
> So, now if the two ionic molecules sodium sulphide and hydrochloric acid react with each other, there will be formation of four ions, two from each molecule, namely, chloride, proton, sodium ion, and sulphide ion. So, we will write the chemical equation for the reaction.
$HCl+N{{a}_{2}}S\to NaCl+{{H}_{2}}S$
> The products formed are sodium chloride and hydrogen sulphide gas. Now in order to balance this equation we need to make sure the number of each atom on both the sides are equal. But we can see that the number of sodium and hydrogen on both the sides are unequal. So, we will add a coefficient two, on hydrochloric acid on the reactant side as well as sodium chloride on the product side, in order to balance it out.
$2HCl+N{{a}_{2}}S\to 2NaCl+{{H}_{2}}S$

Note:
- The reaction of sodium sulphide and hydrochloric acid results in the formation of solid sodium chloride along with the evolution of hydrogen sulphide gas.
- In order to balance an equation, the number of each of the elements should be made equal on both the sides of the reaction, by adding appropriate coefficients.