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Supersaturated Solution

A solution containing more than the saturated amount of dissolved solute in a solution is referred to as supersaturated solution. When we see a solution getting prepared we see the number of solute particles occupying the intermolecular spaces of the solvent and slowly increase the concentration of the solution.

Beyond a point when no more solutes could be dissolved under normal condition we say we have reached a point of saturation. Beyond the point of saturation when no more solutes could be dissolved in the solvent, external resources like stirring, applying heat or boiling the solution mixture, are applied to enforce the process of super saturation.

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Supersaturated Solution Definition

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It is possible for any solution to hold more dissolved solute than normal amount in a saturated solution. These are considered as super saturated solutions. And although these solutions are unstable, the excess solid finally crystalize which is available in solution till the concentration point of equilibrium of the solute is achieved.

The solubility of these substances might lower if the temperature is lowered as well and often the crystallization point is reached even before the process goes through the normal stages.

Super saturation of solutions is usually made by preparing first a saturated solution at a pre-determined temperature and finally cooling it in stages. If the crystallization rate is found to be slow then the solid might not precipitate properly when the solubility is exceeded. Lower temperatures might result in a solution with more solute than the preferred amount in conditions under equilibrium. This finally leads to super saturation. The supersaturated solution definition could be stated simply as the number of solutes which are present in excess than the saturated solution. This might be elaborated when we study the preparation of super saturated solution.

How Can a Solution Become Supersaturated?

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Super saturated solution could be made by any easily dissolving solutes into a solvent which will readily allow the solute molecules to occupy the intermolecular spaces.
  • The solvent with enough inter molecular spaces allows the solute particles to occupy these spaces and continue the process till a saturation point is reached. 
  • The saturation point is reached when no more solutes could be adjusted in the intermolecular spaces of solvent unless the temperature of the solution is raised.
  • Once the temperature of the solution is raised the molecules start vibrating about their mean position after absorbing the heat energy and re-align themselves to allow more solute particles to occupy the intermolecular spaces.
  • The process continues till the number of solute particles in the solution reaches a super saturation point.

How to Make a Supersaturated Solution?

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  • Super saturated solution could be made into by making a sugar solution turning into thick sugar syrup.
  • In sugar syrup solution the sugar is the solute which is dissolved in a solvent of water. This slowly turns into a true solution. This is considered as a true solution as the content of the solution will have same concentration all across the mixture and hence is known as homogeneous. 
  • The ability of the water medium to dissolve the solute sugar might vary with temperature of the solution.
  • This is apparent when we are trying to make candy. The solution is found to be very gritty and however stirring is carried out the solution won’t allow more solutes to dissolve in unless the temperature of the solution is raised.
  • Gradually all the sugar solutes go into the solution as the temperature of the solution is raised slowly and is stirred continuously. 
  • The point of saturation is reached which also signifies that no more solutes could be dissolved at that temperature. The percentage of solute sugar in the water solvent resulting in the solution rises continuously as the water in the solution vaporizes with the rise in temperature. 
  • The entire process of boiling and evaporation results in saturation of the solution and beyond. The percentage of sugar as solute in the solution continues to increase till the final temperature is reached and the super saturated syrup of sugar are removed from heat.
  • Once the syrup is removed from direct heat the solution begins to cool down as it is related to the sugar in the solution. 
  • As more sugar is placed in solution as the syrup is cooled down the super saturated solution becomes more and more unstable. This is due to the theory that less amount of sugar could be dissolved in lower temperature and ideally under lower temperature a very high super saturated level will be formed.

Supersaturated Solution Example

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There could be several super saturated solutions that we could have around us. The list of super saturated solutions is as follows:
  
  •     Sugar syrup solution, which has sugar as solute and water as solvent.
  •     Sugar candy solution, which has sugar along with other flavouring agents as solute and water as solvent.
  •     Dead sea water, which has several minerals as solutes and water as solvent.

These are super saturated solutions as the solutions have more solute than the saturation limit.
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