Experiment 1
Experiment 1
AIM : To recrystallize the given compound using water.
AIM : To recrystallize the given compound using water.
APPARATUS REQUIRED :
APPARATUS REQUIRED :
Sample of compound , Beaker , Water , Spatula , Glass rod , China dish , Tripod stand , Burner , Wire gauge and Filter Paper.
Sample of compound , Beaker , Water , Spatula , Glass rod , China dish , Tripod stand , Burner , Wire gauge and Filter Paper.
THEORY :
THEORY :
Organic compounds synthesized in the laboratory or isolated from natural sources are often contaminated with impurities. Recrystallization is a widely used purification technique for removing impurities from organic compounds that are solid at room temperature. This method relies on the observation that the solubility of a compound in a solvent generally increases with temperature. Conversely, as a solution cools the solubility of a compound will decrease until the solution becomes saturated and crystals form. Recrystallization can produce very pure compounds. The choice of recrystallization solvent is critical. A good recrystallization solvent will not dissolve the solid compound at low temperatures, but will dissolve it at high temperatures. The cold solvent also needs to dissolve the impurities. A typical recrystallization procedure involves dissolving the impure solid in a minimal amount of boiling solvent, followed by a cooling period. If insoluble impurities are found in the sample during heating, additional steps (hot-gravity filtration) are taken to remove them before cooling. After the hot solution cools and reaches the saturation point, small seed crystals of the compound will form in the solution. Slowly, additional molecules of the compound attach to the seed crystal and the crystals grow. Since molecules in the crystals typically have a greater affinity for other molecules of the same type than they do for any impurities, the process of crystal formation gives rise to relatively pure crystals. The impurities originally present in the compound are left in solution.
Organic compounds synthesized in the laboratory or isolated from natural sources are often contaminated with impurities. Recrystallization is a widely used purification technique for removing impurities from organic compounds that are solid at room temperature. This method relies on the observation that the solubility of a compound in a solvent generally increases with temperature. Conversely, as a solution cools the solubility of a compound will decrease until the solution becomes saturated and crystals form. Recrystallization can produce very pure compounds. The choice of recrystallization solvent is critical. A good recrystallization solvent will not dissolve the solid compound at low temperatures, but will dissolve it at high temperatures. The cold solvent also needs to dissolve the impurities. A typical recrystallization procedure involves dissolving the impure solid in a minimal amount of boiling solvent, followed by a cooling period. If insoluble impurities are found in the sample during heating, additional steps (hot-gravity filtration) are taken to remove them before cooling. After the hot solution cools and reaches the saturation point, small seed crystals of the compound will form in the solution. Slowly, additional molecules of the compound attach to the seed crystal and the crystals grow. Since molecules in the crystals typically have a greater affinity for other molecules of the same type than they do for any impurities, the process of crystal formation gives rise to relatively pure crystals. The impurities originally present in the compound are left in solution.
SELECTION OF AN IDEAL SOLVENT:
SELECTION OF AN IDEAL SOLVENT:
In recrystallization, the choice of solvent is very important, which is directly related to the quality of the product, the difficulty of operation, as well as the economic benefits. The following conditions must be considered when selecting solvents:
In recrystallization, the choice of solvent is very important, which is directly related to the quality of the product, the difficulty of operation, as well as the economic benefits. The following conditions must be considered when selecting solvents:
There is no chemical reaction with the purified substance.
There is no chemical reaction with the purified substance.
The solubility of the purified substance in the solvent varies greatly at different temperatures, and the solubility increases with the increase of temperature, while the solubility is very small with the decrease of temperature.
The solubility of the purified substance in the solvent varies greatly at different temperatures, and the solubility increases with the increase of temperature, while the solubility is very small with the decrease of temperature.
The solubility of impurities is very large and remains in the mother liquor after crystallization, or it is so small that it can be filtered and removed.
The solubility of impurities is very large and remains in the mother liquor after crystallization, or it is so small that it can be filtered and removed.
Easy to volatilize and easy to be removed by crystallization separation.
Easy to volatilize and easy to be removed by crystallization separation.
A better crystal shape can be given.
A better crystal shape can be given.
Non-toxic or low toxicity, easy to operate and low price.
Non-toxic or low toxicity, easy to operate and low price.
PROCEDURE :
PROCEDURE :
Take the compound in a watch glass and weigh it.
Take the compound in a watch glass and weigh it.
Dissolve the given compound in 20-30 ml of water in a beaker. Stir it with the help of a glass rod .
Dissolve the given compound in 20-30 ml of water in a beaker. Stir it with the help of a glass rod .
Burn the burner and arrange the tripod stand and wire gauge. Now place the beaker on the heating set up and heat it until the compound dissolves.
Burn the burner and arrange the tripod stand and wire gauge. Now place the beaker on the heating set up and heat it until the compound dissolves.
Place a filter paper in a funnel and filter the solution into a china dish.
Place a filter paper in a funnel and filter the solution into a china dish.
Allow the solution to cool down and wait until its water content evaporates.
Allow the solution to cool down and wait until its water content evaporates.
Now with the help of blotting paper absorb excess water and transfer the remaining content in a china dish and keep it aside.
Now with the help of blotting paper absorb excess water and transfer the remaining content in a china dish and keep it aside.
OBSERVATION : The crystal is observed to be shining white.
OBSERVATION : The crystal is observed to be shining white.
RESULT: After recrystallization of given compound a pure, colorless , crystalline solid appears.
RESULT: After recrystallization of given compound a pure, colorless , crystalline solid appears.
PRECAUTIONS:
PRECAUTIONS:
Ensure that the crystals are washed well.
Ensure that the crystals are washed well.
Avoid overheating of the solution.
Avoid overheating of the solution.
The filtrate should be evaporated slowly by gentle heating of the solution.
The filtrate should be evaporated slowly by gentle heating of the solution.
The solution should be cooled slowly and do not use any rapid cooling procedures.
The solution should be cooled slowly and do not use any rapid cooling procedures.
Pictures related to Experiment
Pictures related to Experiment
Pure crystalline solid with water
Pure crystalline solid with water
Obtained crystals after dehydration
Obtained crystals after dehydration