Rock candy is made by dissolving sugar in warm water to form a saturated solution and then is allowed to cool.

Question

(a) What is rock candy? (in terms of saturated solution oversaturated, chemistry wise, literally..>)

(b) Explain how it is formed based on what you know about saturated solutions.

Thanks.

Answer 1

Typically supercooled liquids are called glass or non-crystalline solids.  The rate of cooling and solidification exceeds the rate of crystal formation.

In this case you have a supersaturated solution that you basically froze as is, rather than allowed it to crystallize and cool along an equilibrium pathway.  That is all that glass is as well.

Answer 2

Well, the warm sugar solution is supersaturated because you are using heat to dissolve more sugar than room temperature would allow.

As the solution cools, it can no longer remain supersaturated. The excess sugar that cannot be held precipitates out into a solid.

Answer 3

Rock candy is recrystallized sucrose.

As the solution cools, it become supersaturated, and crystals of sugar start to come out of solution (assuming they have nucleation sites).  The more the solution cools, the more sugar comes out of solution, until the crystals of rock candy are in equilibrium with a saturated solution of sugar.

DK