Cambridge Lower Secondary Checkpoint Science: Chemistry III: Changes to Materials

Changes to materials (reactions and energy ideas)

Question 1 of 30

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Physical vs chemical change (tricky evidence):

A student heats a blue crystalline solid \(X\) in a dry test tube. The crystals turn white and droplets appear on the cooler part of the tube. After cooling, the student adds a few drops of water to the white solid and it turns blue again.

Which conclusion is the best supported by the observations?

Select one option.

The main change is physical because water was removed and can be added back to restore the original substance.
The main change is chemical because a colour change always proves a chemical reaction.
The change must be combustion because heating was involved.
The change must produce a gas because droplets formed.
The change is irreversible because heating always makes new substances.

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