Molten sucrose can solidify into two distinct forms depending on the cooling conditions
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Molten sucrose can solidify into two distinct forms depending on the cooling conditions. In an experiment, equal masses of molten sucrose are subjected to two different cooling protocols:
• Cooling Protocol A: The liquid is allowed to cool very slowly, decreasing in temperature by only 0.2 °C min⁻¹.
• Cooling Protocol B: The liquid is poured onto a copper plate at 20 °C, solidifying within seconds.
The resulting solids are labeled Solid A and Solid B, respectively.
(a) Identify the type of solid most likely formed under each cooling protocol (crystalline or amorphous). Explain the role of cooling rate in producing the observed structures.
(b) Solid B is optically transparent and can be bent slightly before fracturing, whereas Solid A is opaque and fractures along flat faces. Relate these macroscopic observations to the underlying particle arrangements in each solid.
(c) Describe how you could convert a portion of Solid B into the same structural form as Solid A without adding any chemicals. Outline the physical steps and explain why they would be effective.
(d) A student claims that Solid B should dissolve in water faster than Solid A at room temperature even though they have identical chemical composition. Evaluate this claim using structural arguments.