Question

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?

Answer 1

When copper carbonate is heated, it decomposes to form a black residue. This black residue is actually copper(II) oxide. Along with this black residue, carbon-dioxide is released.

The law of conservation of mass holds true. 123.6 g of copper carbonate decomposes to 79.6 g of copper oxide and (123.6 g-79.6 g=44 g) 44 g of carbon-dioxide.

Answer 2

No it does not. This is the answer because the Law Of Conservation Of Mass says that mass remains constant during the change. As you can see, the mass was 123.6g, and it is now 79.6 g.