how will you purify a sample of impure sugar
Answers
Answer:
Our Objective
Our Objective is to prepare the crystals of the following substances form their impure samples through crystallisation;
Copper sulphate
Potash alum
Benzoic acid
The Theory
What happens during crystallisation?
The chemicals used for various purposes should be pure, completely free from any type of impurities. Method of purification of a substance depends upon the nature of impurities present in it. There are various methods for the purification of substances, e.g., filtration, evaporation, decantation, distillation, and crystallization. Crystallisation is one of the very important purification techniques, purifying substances by removing unwanted by-products. Crystalline compounds are generally purified via this crystallisation process.
The principle behind the crystallisation is that the amount of solute that can be dissolved by a solvent increases with temperature.
In crystallisation, the impure substance is dissolved in a suitable solvent to reach its nearly saturated solution at a temperature higher than the room temperature. At this high temperature, the solute has very high solubility in that solvent, so a much smaller quantity of hot solvent is needed for dissolving the solute than the solvent at room temperature. When the solution is cooled, the pure substance is crystallised. The solution left behind is called mother liquor. All the impurities are left behind in the mother liquor. The purification method depends on the differences in solubility between the compound and the impurity. Crystallisation of Potash Alum
Potash alum is highly water soluble. To prepare pure crystals of potash alum, dissolve the sample in distilled water and remove the insoluble impurities by filtration. This solution is concentrated to the crystallisation point and cooled. Colourless transparant crystals of potash alum separate. The soluble impurities are left behind in the mother liquor. Potash alum has an octahedral geometry.
Answer:
by recrystallization
Explanation:
Add a small quantity of appropriate solvent to an impure solid.
Apply heat to dissolve the solid.
Cool the solution to crystallize the product.
Use vacuum filtration to isolate and dry the purified solid.