Can some one explain the principles involved in crystallization process of purification? What factors lead to the separation of impurities from solute?

Crystallisation is a separation technique that is used to separate a solid that has dissolved in a liquid and made a solution. The solution is warmed in an open container, allowing the solvent to evaporate, leaving a saturated solution. A solution that has as much solid dissolved in it as it can possibly contain is called a saturated solution. As the saturated solution is allowed to cool, the solid will come out of the solution and crystals will start to grow. The crystals can then be collected and allowed to dry. A solid that does not dissolve in a liquid can be separated by filtration. The size of crystals depends on the rate of cooling. Fast cooling will result in a large number of small crystals. Slow cooling will result in a smaller number of large crystals. read less

Crystallization is basically a property associated with pure substances. As Lakhshmi above clearly said that it is based on the principles of solubility: compounds (solutes) tend to be more soluble in warm and high temperature liquids (solvents) than they are in cold liquids. If a saturated high temperature solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration. molecular recognition is the principle of purification in crystallization.The main factors influencing solubility are, as we saw above: Concentration Temperature So we may identify two main families of crystallization processes: Cooling crystallization Evaporative crystallization read less

if we go on adding sugar to water then a level will be reached beyond which no more sugar could be added. then we have to heat the mixture on stove. then we can dissolve more sugar. if we dissolve more sugar and allow it to cool then the extra sugar added after heating will no longer stay in dissolved form but will separate from water. we will get pure crystals of sugar. this process is called crystallization. read less