During recrystalization of acetanilide, an orange solution of a compound in hot alcohol was treated in activated carbon and then filtered through a filter paper. On cooling the filtrate gave gray crystals, although the compound was reported to be colourless. Explain why the crystals were gray and describe steps taken to obtain a colourless product
You did this in your procedure unless you did a dry lab so you should know what steps you took to obtain the correct crystals.
The gray color of the crystals obtained during the recrystallization process of acetanilide could be due to impurities present in the compound and/or incomplete removal of impurities during the process. To obtain a colorless product, you can follow these steps:
1. Dissolving the acetanilide in hot alcohol: Start by dissolving the acetanilide in a suitable solvent, such as hot ethanol or methanol. Ensure that the solution is heated enough to completely dissolve the compound.
2. Treatment with activated carbon: Add a small amount of activated carbon to the hot solution, and stir it continuously for a few minutes. The activated carbon will adsorb the impurities present in the solution, leading to their removal.
3. Filtration: After treating the solution with activated carbon, it needs to be filtered to remove any insoluble impurities and the activated carbon itself. Use a filter paper and a funnel to filter the solution. This process will yield a clear filtrate.
4. Cooling: Allow the filtrate to cool gradually to promote slow and controlled crystal growth. This step helps in obtaining larger, purer crystals.
5. Crystallization: As the solution cools down, the solubility of acetanilide decreases, resulting in the formation of crystals. If impurities are still present, they can be embedded within the growing crystals, leading to their grayish appearance. The slower the cooling process, the better the chances of obtaining colorless crystals.
6. Washing and drying: Once the crystals have formed, they need to be separated from the remaining liquid. This can be achieved by using a vacuum filtration setup. After filtration, wash the crystals with a small amount of cold solvent to remove any leftover impurities. Finally, dry the crystals thoroughly to remove any remaining solvent.
By following these steps, you should be able to obtain a purer and potentially colorless product of acetanilide.
The gray color observed in the crystals obtained during the recrystallization of acetanilide can be attributed to the presence of impurities that were not effectively removed during the process. Acetanilide is a colorless compound, so the presence of these impurities resulted in the observed coloration.
To obtain a colorless product, it is important to follow certain steps during the recrystallization process:
1. Dissolving: Start by dissolving the crude acetanilide in a suitable solvent, such as hot ethanol or methanol. Heating the solvent helps ensure complete dissolution of the compound.
2. Activated Carbon Treatment: In your case, activated carbon was used to remove impurities from the solution. Activated carbon has a highly porous structure that adsorbs impurities. It is added to the hot solution, stirred thoroughly, and then allowed to settle. After settling, the mixture is filtered through a filter paper to separate the activated carbon along with the adsorbed impurities. This step helps in removing colored impurities and increases the chance of obtaining a colorless product.
3. Slow Cooling: After the activated carbon treatment and filtration, the solution should be slowly cooled down to encourage the formation of pure crystals. Slow cooling allows the molecules to arrange themselves in an ordered manner, resulting in the formation of larger, purer crystals.
4. Filtration: Once the solution has cooled down, it is filtered using a filter paper to isolate the crystals. This filtration step helps in separating the solid crystals from the remaining liquid.
5. Washing: To further remove any remaining impurities, the obtained crystals can be washed with a small amount of ice-cold solvent. The cold solvent helps in dissolving any residual impurities while leaving the pure crystals behind.
6. Drying: Lastly, the colorless crystals are dried thoroughly to remove any traces of the solvent. This can be done using techniques like air drying or gentle heating under vacuum.
By following these steps, the likelihood of obtaining a colorless product will be greatly increased. However, it is important to note that the purity of the final product can be influenced by factors such as the quality of starting materials, technique, and the thoroughness of the purification steps.