A student mixes aqueous solutions of Pb(NO3)2 and KI and immediately observes the…
CHEMISTRY · Single correct · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A student mixes aqueous solutions of Pb(NO3)2 and KI and immediately observes the formation of an opaque, yellow solid suspended in the liquid. Which statement best justifies classifying the observed change as chemical rather than physical?
(a) The cloudiness shows that the solution cooled and lead(II) ions simply came out of solution without undergoing any bond changes.
(b) The yellow solid represents a physical separation of phases, analogous to condensation, so no new substances are produced.
(c) The formation of a yellow precipitate shows that lead(II) ions and iodide ions have combined to create a new compound, PbI2, whose composition differs from the dissolved ions.
(d) The observed color results only from the scattering of light by iodide ions already present, indicating a reversible physical process.