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Why does a supersaturated solution not precipitate the solute upon gradually cooling?
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Ken Morris
Why does a supersaturated solution not precipitate the solute upon gradually cooling?
A solution with a precipitate that is not dissolving is saturated. A supersaturated solution arises when a saturated solution is cooled (when solubility decreases with temperature, which is most often the case). The presence of solid mixed with the solution usually prevents supersaturation, as the solid surfaces of the precipitate will serve as good nucleation sites for additional precipitation if the solution begins to reach supersaturation.
A solution with a precipitate that is not dissolving is saturated. A supersaturated solution arises when a saturated solution is cooled (when solubility decreases with temperature, which is most often the case). The presence of solid mixed with the solution usually prevents supersaturation, as the solid surfaces of the precipitate will serve as good nucleation sites for additional precipitation if the solution begins to reach supersaturation.
Because [math] ext{supersaturation}[/math] describes a NON-EQUILIBRIUM scenario, where, for some reason, thermodynamic equilibrium has not been attained… After equilibrium has been reached, what do we call the solution…?
Because [math]ext{supersaturation}[/math] describes a NON-EQUILIBRIUM scenario, where, for some reason, thermodynamic equilibrium has not been attained… After equilibrium has been reached, what do we call the solution…?
Supersaturation is a condition where a ppt should form of the solute, but does not. At this writing, 10 other answers have been given. Many note that this is an unstable situation. An argument I did not see in the answers is as follows.
First, to get supersaturated solutions to not precipitate, it is best to use very clean vessels and do not disturb them. Under these conditions, the solution will remain supersaturated. But, do something like add a tiny crystal and a ppt immediately forms (as noted by Robert Kern). So, some have proposed that the supersaturated solution stays this way because it needs a template to start forming a crystal. Dirt on the vessel might have something on its surface that looked like the crystal should look and templates it. Alternatively, scratch the inner surface of the vessel with the supersaturated solution, and ppt my start. Here, some portion of the scratch may resemble the crystal and then ppt will commence.
Supersaturation is a condition where a ppt should form of the solute, but does not. At this writing, 10 other answers have been given. Many note that this is an unstable situation. An argument I did not see in the answers is as follows.
First, to get supersaturated solutions to not precipitate, it is best to use very clean vessels and do not disturb them. Under these conditions, the solution will remain supersaturated. But, do something like add a tiny crystal and a ppt immediately forms (as noted by Robert Kern). So, some have proposed that the supersaturated solution stays this way because it needs a template to start forming a crystal. Dirt on the vessel might have something on its surface that looked like the crystal should look and templates it. Alternatively, scratch the inner surface of the vessel with the supersaturated solution, and ppt my start. Here, some portion of the scratch may resemble the crystal and then ppt will commence.
The solute molecules need a little more energy to overcome some kind of energy barrier before they can form crystals and precipitate. Disturbing the solution in some way gives them enough energy to collide productively.
The solute molecules need a little more energy to overcome some kind of energy barrier before they can form crystals and precipitate. Disturbing the solution in some way gives them enough energy to collide productively.
A solution with a precipitate that is not dissolving is saturated. A supersaturated solution arises when a saturated solution is cooled (when solubility decreases with temperature, which is most often the case). The presence of solid mixed with the solution usually prevents supersaturation, as the solid surfaces of the precipitate will serve as good nucleation sites for additional precipitation if the solution begins to reach supersaturation.
A solution with a precipitate that is not dissolving is saturated. A supersaturated solution arises when a saturated solution is cooled (when solubility decreases with temperature, which is most often the case). The presence of solid mixed with the solution usually prevents supersaturation, as the solid surfaces of the precipitate will serve as good nucleation sites for additional precipitation if the solution begins to reach supersaturation.
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Because [math] ext{supersaturation}[/math] describes a NON-EQUILIBRIUM scenario, where, for some reason, thermodynamic equilibrium has not been attained… After equilibrium has been reached, what do we call the solution…?
Because [math]ext{supersaturation}[/math] describes a NON-EQUILIBRIUM scenario, where, for some reason, thermodynamic equilibrium has not been attained… After equilibrium has been reached, what do we call the solution…?
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Supersaturation is a condition where a ppt should form of the solute, but does not. At this writing, 10 other answers have been given. Many note that this is an unstable situation. An argument I did not see in the answers is as follows.
First, to get supersaturated solutions to not precipitate, it is best to use very clean vessels and do not disturb them. Under these conditions, the solution will remain supersaturated. But, do something like add a tiny crystal and a ppt immediately forms (as noted by Robert Kern). So, some have proposed that the supersaturated solution stays this way because it needs a template to start forming a crystal. Dirt on the vessel might have something on its surface that looked like the crystal should look and templates it. Alternatively, scratch the inner surface of the vessel with the supersaturated solution, and ppt my start. Here, some portion of the scratch may resemble the crystal and then ppt will commence.
Supersaturation is a condition where a ppt should form of the solute, but does not. At this writing, 10 other answers have been given. Many note that this is an unstable situation. An argument I did not see in the answers is as follows.
First, to get supersaturated solutions to not precipitate, it is best to use very clean vessels and do not disturb them. Under these conditions, the solution will remain supersaturated. But, do something like add a tiny crystal and a ppt immediately forms (as noted by Robert Kern). So, some have proposed that the supersaturated solution stays this way because it needs a template to start forming a crystal. Dirt on the vessel might have something on its surface that looked like the crystal should look and templates it. Alternatively, scratch the inner surface of the vessel with the supersaturated solution, and ppt my start. Here, some portion of the scratch may resemble the crystal and then ppt will commence.
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The solute molecules need a little more energy to overcome some kind of energy barrier before they can form crystals and precipitate. Disturbing the solution in some way gives them enough energy to collide productively.
The solute molecules need a little more energy to overcome some kind of energy barrier before they can form crystals and precipitate. Disturbing the solution in some way gives them enough energy to collide productively.
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VOTE