A light green powder is heated in a test tube. A gas is given off, and the solid becomes black. Was the change physical or chemical, and is the green powder an element, a compound, or a mixture?

1 Answer
Jan 18, 2016

Answer:

See explanation

Explanation:

The question describes an experiment similar to the decomposition of copper(II) carbonate (#CuCO_3#) which is when heated in decomposes into carbon dioxide gas (#CO_2#) and copper(II) oxide (#CuO#) according to the following decomposition reaction:

#color(green)(CuCO_3(g))->color(gray)(CO_2(g))+CuO(s)#

Therefore, the green substance is a compound and the change is a chemical change since giving off a gas is one of the several indication of a chemical change that include:

  1. Gas evolution
  2. Formation of a precipitate
  3. Evolution of heat
  4. Odor
  5. Color change
  6. etc.

Here is a video on physical and chemical change that describes the aforementioned experiment:

Lab Experiment #2: Physical & Chemical Changes.