A student performs four separate laboratory demonstrations intended to illustrate the…
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A student performs four separate laboratory demonstrations intended to illustrate the difference between physical and chemical change. In each demonstration, the student records a macroscopic observation.
Observation I A strip of magnesium ribbon is ignited in air and burns with an intense white light.
Observation II Liquid ethanol is placed in an open petri dish and left on the lab bench; after several minutes the liquid has disappeared.
Observation III Solid iodine is gently warmed; a purple vapor forms above the crystals and then re-deposits as shiny plates on a cold watch glass.
Observation IV Aqueous solutions of silver nitrate and sodium chloride are combined; a white, insoluble solid appears in the mixture.
Use the observations to analyze how experimental evidence is used to decide whether a chemical change has taken place.
(a) Define the term “chemical change” in the context of macroscopic observations and particle-level events.
(b) For each of the four observations, state whether the change is most reasonably classified as chemical or physical. Support EACH classification with a specific explanation that relates the macroscopic observation to the particle-level events taking place.
(c) Choose ONE observation that you classified as a chemical change. Describe an additional, independent piece of evidence (not already listed) that you could obtain in the laboratory to strengthen the conclusion that a chemical change has occurred.
(d) Discuss one limitation of relying on a single type of macroscopic evidence when distinguishing chemical from physical change in an experimental setting.