HKDSE Chemistry Question Review 2020-07-28

1. Explain microscopically what physical change and chemical change are.

Solution:

Physical changes involve changes other than the electronic configuration of the atoms of a substance, whereas chemical changes are otherwise.

For example, beta decay in nuclear physics deals with changes in the nucleus of atoms without altering the electronic structures, so it is a physical change. On the other hand, redox reactions involve electron transfer between 2 substances such that the electronic structures are changed, so it is chemical change.

2. Show that Copper is a transition metal.

Solution:

The ionic compound of Copper have more than 1 color. CuO is black but Cu2O is brick red.

Strictly speaking, complex salts are NOT purely ionic as they involve dative bondings, so suggesting CuSO4 as blue and CuCl2 ad green is a WRONG approach.

as* green