Row Colour change of solid Liquid formed A blue to white water B white to blue water C no change none D blue to green oil The diagram shows hydrated copper(...
Question 1 Report
| Row | Colour change of solid | Liquid formed |
|---|---|---|
| A | blue to white | water |
| B | white to blue | water |
| C | no change | none |
| D | blue to green | oil |
The diagram shows hydrated copper(II) sulfate being heated in a test tube. The table lists possible observations. Which row correctly describes what is seen during and after heating?
Answer Details
Hydrated copper(II) sulfate is blue because of the water of crystallisation locked into its lattice. Heating drives that water off as steam:
\[\mathrm{CuSO_4\cdot 5H_2O\ (blue)} \rightleftharpoons \mathrm{CuSO_4\ (white)} + 5\mathrm{H_2O}\]
So during heating the solid changes from blue to white, and the vapour labelled in the diagram condenses to colourless water at the cooler upper part of the tube. The row recording a blue to white colour change with water as the liquid formed is the one that matches.
White to blue describes the reverse change, seen when water is dripped onto the cooled anhydrous solid, which also releases heat. No oil is produced, since nothing organic is present, and there is certainly a visible change, so the row reporting nothing happening is ruled out by the observation.
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