Final answer:
After evaporating all the water from the copper sulphate solution, copper sulphate crystals would be left in the dish. These would be white due to the loss of water of crystallization, indicating a transformation from a hydrated to an anhydrous salt.
Step-by-step explanation:
When Bruce poured copper sulphate solution into a dish and left it in a warm room, the water from the solution would evaporate due to the heat and the conditions of the room. After five days, the water would have completely evaporated, leaving copper sulphate crystals behind in the dish.
These crystals would be white in color because they've lost their water of crystallization, which originally gave the copper sulphate its blue color. This process is a demonstration of the transformation of a hydrated salt to an anhydrous salt.
Similar to the experiment where magnesium sulphate is heated until all the water is evaporated, the weight difference can be used to determine the amount of water that was in the copper sulphate solution.
In Bruce's case, the substance left in the dish would be an anhydrous form of copper sulphate, known as copper(II) sulfate pentahydrate when hydrated.
This process is important in chemistry to understand the properties and compositions of substances, which can also be observed when conducting experiments with other salts, such as magnesium sulphate.