A mixture of powdered iron and powdered sulfur is placed in a test tube
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A mixture of powdered iron and powdered sulfur is placed in a test tube. A magnet is able to separate most of the iron from the sulfur. The test tube is then heated strongly until the contents glow red. After cooling, a hard, brittle, black solid remains that is not attracted to a magnet.
The symbolic representations are
Before heating: Fe(s) + S8(s) (mixture)
After heating: 8 Fe(s) + S8(s) → 8 FeS(s) (black solid)
(a) Describe the compositional difference between the sample before heating and the sample after heating.
(b) Design an experimental test (other than magnetism) that would allow a student to distinguish between an unreacted iron–sulfur mixture and the black solid product. Describe the expected observations for both samples.
(c) Using atomic-level reasoning, explain why the properties of the black solid differ from those of the original mixture.
(d) Classify the heating step as a physical or chemical change and justify your classification using evidence from parts (a) and (b).