During an investigation, a scientist heated 123.6 g of copper carbonate till it decomposed to form a black residue. the total mass of the black residue formed was 79.6 g. does the law of conservation of mass hold true in this case? use complete sentences to justify your answer based on numerical calculations

See below explanation

Explanation:

The correspondent chemical reaction for copper carbonate decomposed by heat is:

CuCO₃ (s) → CuO (s) + CO₂ (g)

Considering all molar mass (MM) for each element ( we consider rounded numbers) :

MM CuCO₃ = 123 g/mol

MM CuO = 79 g/mol

MM CO₂ = 44 g/mol

Statement mentions that scientis heated 123.6 g of CuCO₃ (almost a MM), until a black residue is obtained, which weights 79.6 g : this solid residue is formed by CuO, and the remaining mass (approximatelly 44 g) belongs to teh second product, this is, CO₂; as it is a gas compund, it is not certainly included on the solid residue.

So, law of conservation mass is true for this case, since: 123.6 g = 79.6 g + 44 g. As explained, on the solid residue, we don not include the 44 g, which  "escaped" from our system, since it is a gas compound (CO₂)

when it gains or loses electrons

measure their densities same density, same sub