Question

Assertion: Concentrated aqueous solution of $CuC{l_2}$ is green in colour.
Reason: The solution contains two complex ions i.e. ${[Cu{({H_2}O)_4}]^{2 + }}$ and ${[CuC{l_4}]^ - }$ in equilibrium.
(A) Both assertion and reason are correct and reason is the correct explanation for assertion
(B) Both assertion and reason are correct but reason is not the correct explanation for assertion
(C) Assertion is correct but reason is incorrect
(D) Assertion is incorrect but reason is correct

Answer 1

Solid copper chloride $(CuC{l_2})$ is green in colour. When a salt dissolves in solvent, the solvent molecules dissolve the ions by ionic attractions. Copper can form covalent coordinate bonds and thus it forms metal complexes.

Complete Step-by-Step Solution:
We will find whether the assertion and reason is true or not.
- The hydrated salt of $CuC{l_2}$ is green in colour. However, the anhydrous copper chloride is not coloured at all. Here, we are talking about the colour of the aqueous solution of copper chloride. The colour of copper chloride solution in water is blue green. Actually, when the solution is dilute, the colour of the solution is blue and when the solution is concentrated, the colour of the solution is green.
- We know that when a salt gets dissolved in water, the ions get solvated by the solvent molecules. Same way, a copper cation gets solvated by four molecules of water and makes a complex.
- Some free chloride ions get coordinated to copper chloride to make ${[CuC{l_4}]^{2 - }}$.
- However, none of the complexes are responsible for the green colour of the solution. Actually, the copper atom has 9 electrons in its d-orbital which makes d-d transition easier and this is the reason why the solution appears green in colour.
-Thus, we can conclude that both assertion and reason are correct statements but reason is not the correct explanation for assertion.

So, the correct answer is (B).

Note: Remember that even though copper chloride is green solid, it gives blue coloured solution when its solution is dilute in concentration. However, the concentrated solution of copper chloride in water is green in colour.