A pupil heated 1.24 g of copper carbonate strongly. The chemical reaction which took place is represented by the equation:

CuCO3(s) → CuO(s) + CO2(g)

He then heated the 0.80 g of solid again. When he weighed it after cooling, its
mass was still 0.80 g. Explain why it had not changed in mass this time.

After the solid which remained had cooled, he weighed it.

He found that its mass was 0.80 g.

(i) Why did the pupil find a decrease in mass in this experiment?

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).