A research group investigates three sealed samples labelled A, B

CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions

Problem

A research group investigates three sealed samples labelled A, B, and C. Each sample is subjected to a heating–cooling cycle inside a closed reaction vessel attached to a gas-collection syringe. Observational data are recorded in the table below.

Sample	Initial mass of vessel (g)	Final mass of vessel (g)	Visual observations during heating	Volume change of gas syringe	Residue appearance after cooling
A	125.00	125.00	Clear liquid becomes clear vapor; no colour change	Syringe volume increases by 40 mL and returns to original upon cooling	None; liquid condenses fully
B	140.00	140.00	Colourless solution turns reddish-brown; solid particles appear	No measurable syringe change	Reddish-brown solid settles at bottom
C	118.50	118.50	White crystals disappear into colourless liquid; temperature change negligible	Syringe volume unchanged	Clear solution remains after cooling

Use the data to answer parts (a)–(d). (a) For Sample A, determine whether a physical or chemical change predominates. Cite all relevant evidence from the table in your justification. (b) For Sample B, determine whether a physical or chemical change predominates. Cite all relevant evidence from the table in your justification. (c) Compare the particulate-level models that account for the observations in Samples A and B. In your comparison, explicitly address (i) identity of particles, (ii) types of intermolecular or intraparticle forces disrupted or formed, and (iii) conservation of mass. (d) The classification of Sample C is ambiguous based solely on the given data. Design one additional, feasible experimental test that would allow you to distinguish conclusively between a physical and a chemical change for Sample C. State what result you would expect for each possible outcome and how it would inform your conclusion.

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