Question

Crystals of copper sulphate are heated in a test tube for some time. What is the colour of copper sulphate (i) before heating and (ii) after heating? What are the source liquid droplets seen on the upper side of the test tube during the heating process?

Answer 1

Hint: Try to recall that when crystals of copper sulphate are heated in a test tube for some time then it undergoes a reversible physical chemical change. Now by using this you can easily answer the given questions.
Complete answer:
The steps involved in heating of crystals of copper sulphate are as follows:
Step 1:Firstly, a small amount of copper sulphate crystals is taken in a dry boiling tube
Step 2: In this step, the boiling test tube is heated over the flame on Bunsen burner and the tube is held with the help of a test tube holder.
Step 3: In this step, the colour change is observed after heating the tube for some time.
Step 4: In this step, some water droplets are observed along the sides of the boiling test tube.
Step 5: Finally, in this step, the boiling tube is removed from the flame and is allowed to cool for some time.
During this process of heating, it has been observed that before heating crystals of copper sulphate are blue in colour. But after heating, the colour changes from blue to white.
\[\begin{gathered}
  CuS{O_4}.5{H_2}O(s)\xrightarrow{{heating}}CuS{O_4}(s) + 5{H_2}O
  (blue){\text{ (white)}}
\end{gathered} \].

This happens because crystals of copper sulphate lose the water of crystallisation on heating and it becomes anhydrous copper sulphate and also, the lost water of crystallisation are seen as water droplets on the upper side of the test tube.

Note: It should be remembered to you that on adding water anhydrous copper sulphate changes back to hydrated copper sulphate.
Also, you should remember that while performing this heating process, always try to keep the mouth of the test tube away from your face.