A student heats blue hydrated copper(II) sulfate crystals in a dry test tube. A white solid remains and water droplets collect higher up the tube.
After the apparatus cools, the student tips the tube so that the water runs onto the white solid. The solid becomes blue again.
Which statement explains these observations?
Heating decomposes the crystals into a new white compound; adding water then forms a blue compound that is not copper(II) sulfate.
Heating dissolves the blue crystals in released water and leaves white material; adding the water deposits the blue crystals again.
Heating removes water from hydrated copper(II) sulfate, leaving the white anhydrous solid; adding water reverses the change.
Heating evaporates water trapped around unchanged crystals; adding it back only wets the crystals and restores their blue appearance.
124 exam-style questions on OCR GCSE Chemistry 5.3 Equilibria, covering 5.3.1 Reversible reactions and dynamic equilibrium and 5.3.2 Changing the position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.