Question

A solution of \[CuS{{O}_{4}}\] in water is_________ in colour.
(a) Pink
(b) Blue
(c) Colourless
(d) Green

Answer 1

Hint: The reaction between Cuso4 and water is an example of reversible reactions. In a reversible reaction, the products can again be used to react, producing the original reactants as a result.

Complete step by step solution:

When copper sulfate (\[CuS{{O}_{4}}\]) is dissolved in water, it reacts with water (\[{{H}_{2}}O\]) and forms the product which is again copper sulfate. However, it is now in a hydrated form of the salt and has 5 water molecules attached to it. As a result, the product is now called copper sulfate pentahydrate. The chemical reaction can be given as:

\[CuS{{O}_{4}}+5{{H}_{2}}O\to CuS{{O}_{4}}.5{{H}_{2}}O\]

Here we can see that the copper sulfate reacts with water in a 1:5 ratio, giving the final product as copper sulfate pentahydrate. The anhydrous Copper sulfate salt has a pale green color, whereas the resultant hydrated salt, copper sulfate pentahydrate has a blue color which gives the whole solution a blue appearance.

Additional Information:

Copper sulfate has various uses in industry and research.
It is toxic to microorganisms and is commonly used in insecticides and pesticides. For example, rainwater harvesting systems are cleaned with a solution of copper sulfate before the first rain, to make sure no biological contamination is present.
It is used in Benedict’s solution and in Fehling’s solution to test for reducing sugars.

So, the correct option is (b).

Note: When \[CuS{{O}_{4}}\] is dissolved in water the solution becomes much warmer than the water was before the \[CuS{{O}_{4}}\]was added, indicating heat is being released to the water by the \[CuS{{O}_{4}}\] dissolving process. It is an exothermic process.