Question

Will double displacement reaction occurs between copper $\left( {||} \right)$ sulphate and hydrochloric acid? Why or why not?

Answer 1

In this question we have to check whether double displacement reaction occurs or not within the given elements. We know that in a double displacement reaction the ions of reactants exchange their places to form a new product. We should know that double displacement reaction is also called salt metathesis.

Complete answer:
As we know that we have here two elements i.e. copper $\left( {||} \right)$ sulphate and hydrochloric acid.
We can write them also as $C{u_2}S{O_4}$ and $HCl$ . We know that when we mix both of these soluble compounds, these are completely dissociated in aqueous solution.
In order for a double replacement reaction to take place, we need the reaction to produce an insoluble compound that precipitates out of solution.
Then this reaction will produce copper chloride $CuC{l_2}$ and sulphuric acid i.e. ${H_2}S{O_4}$ .
We can write the above reaction also as:
$CuS{O_4}_{(acq)} + 2HC{l_{(acq)}}\xrightarrow{{}}CuC{l_2}_{(acq)} + {H_2}S{O_4}_{(acq)}$ .
We know that all the ions of these reactions are spectator ions which means that they can be found on both sides of the reaction.
It can be represented as:
$C{u^{2 + }} + SO_4^{2 - } + 2{H^ + } + 2C{l^ - }\xrightarrow{{}}C{u^{2 + }} + 2C{l^ - } + 2{H^ + } + SO_4^{2 - }$
We should note that the above reaction only happens if we take sulphuric acid to dissociate completely in aqueous solution i.e. if we take its second ionization to be complete as well.
If we do not do that we can write it also as: $C{u^{2 + }} + SO_4^{2 - } + 2{H^ + } + 2C{l^ - }\xrightarrow{{}}C{u^{2 + }} + 2C{l^ - } + {H^ + } + HSO_4^ -$ .
Then the net ionic equation will be
$SO_4^{2 - } + 2{H^ + } \xrightarrow{{}} HSO_4^ -$ .
From the above reactions we can see that we were supposed to complete both of sulphuric acid’s ionizations completely but in the above solution , this reaction does not take place because all species exist as ions in aqueous solution.
Hence the double displacement reaction does not take place between copper $\left( {||} \right)$ sulphate and hydrochloric acid.

Note:
We should note that in the above reaction there will also be a colour change i.e. the change in colour from light blue to green that could be observed from a chemical reaction between $CuS{O_4}$ and $HCl$ .
We should know that once $C{u^{2 + }}$ gets dissolved in water, it will form the complex ion ${\left[ {Cu{{({H_2}O)}_6}} \right]^{2 + }}$ which has a light blue colour, however when $HCl$ is added, it will from the complex ion ${\left[ {CuC{l_4}} \right]^{2 - }}$ which has a green colour.