A student notices that when a dilute aqueous iodine solution (yellow-brown) is added…
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A student notices that when a dilute aqueous iodine solution (yellow-brown) is added to a beaker containing a suspension of cornstarch, the mixture turns deep blue-black. When the beaker is subsequently heated for several minutes, the blue-black color gradually disappears and the mixture becomes colorless.
Assume that only thermal energy is supplied; no additional reagents are introduced after the initial mixing.
(a) Identify two distinct pieces of observable evidence in the scenario above that could—when properly interpreted—help distinguish whether the disappearance of the blue-black color upon heating represents a physical change or a chemical change.
(b) For each piece of evidence identified in part (a), explain at the particulate (molecular) level how it supports classification of the heating step as either a physical change or a chemical change.
(c) Propose one modification to the experiment that would provide an additional, independent line of evidence about the nature of the change, and justify how the added evidence would strengthen the conclusion.