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? Use complete sentences to justify your answer based on numerical calculations.

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 complete reaction is the following:

$CuCO_3\to CuO(s)+CO_2(g)$

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.