Separating a mixture of benzoic acid, acetanilide in dichloromethane
An over zealous student decided to conduct this experiment by distilling all the dicholoromethane at the very beginning and then separating the solid residue of benzoic acid and acetanilide by rechrystallization. Explain why this procedure would be ineffective.
sodium hydrogen carbonate was added so the benzoic acid would dissolve hence leaving the acetanilide and dichloroethane. the benzoic acid and the sodium hydrogen bicarbonate was separated buy adding hydrocholoric acid and then using a suction funnel therefore leaving the "pure" benzoic acid. the acetanilide and dicholoroethane was separated via distillation as the dicholoroethane evaporated off leaving the "pure" acetanilide... THIS IS HOW IT WAS ORGINALLY DONE!
The procedure described, distilling all the dichloromethane at the beginning and then separating the solid residue of benzoic acid and acetanilide by recrystallization, would be ineffective for several reasons:
1. Distillation alone cannot effectively separate a mixture of solid compounds like benzoic acid and acetanilide. Distillation is typically used to separate liquid mixtures based on differences in boiling points. In this case, both benzoic acid and acetanilide are solids at room temperature and distilling the solvent will not separate them.
2. Dichloromethane is a common solvent for recrystallization, and removing it entirely at the beginning would eliminate the solvent needed for the recrystallization process. Recrystallization relies on dissolving the mixture in a suitable solvent, heating it to dissolve the compounds, and then allowing it to slowly cool to allow for crystallization. By removing the dichloromethane, there would be no solvent available for recrystallization.
3. Benzoic acid and acetanilide have different solubilities in most solvents, including dichloromethane. By dissolving the mixture in dichloromethane and then removing the solvent, there is a higher chance of losing one or both of the compounds. They might dissolve in the solvent unevenly and not completely recrystallize, leading to loss or mixed crystals.
4. The process of recrystallization is generally used to purify a compound by removing impurities. By distilling the solvent at the beginning, there is a risk of losing some of the desired compounds, as impurities could be trapped within the crystals or dissolved in the solvent. The recrystallization step is crucial for purification and obtaining pure benzoic acid and acetanilide.
In summary, distilling all the dichloromethane at the beginning and then separating the solid residue of benzoic acid and acetanilide by recrystallization is an ineffective procedure because it does not utilize the appropriate separation techniques and fails to maintain the necessary solvent for the recrystallization process.
The procedure described, distilling all the dichloromethane at the beginning and then separating the solid residue by rechrystallization, would be ineffective for separating a mixture of benzoic acid and acetanilide. Here's why:
1. Distillation: Distillation is a technique used for separating liquids based on differences in boiling points. In this case, dichloromethane (boiling point around 40°C) and benzoic acid (boiling point around 250°C) have significantly different boiling points. However, acetanilide has a boiling point similar to dichloromethane (around 135°C). Therefore, distilling all the dichloromethane would also lead to the loss of acetanilide, as it would be carried over with the distillate.
2. Rechrystallization: Rechrystallization is a technique used to purify solid compounds based on differences in solubility. However, in this case, both benzoic acid and acetanilide are soluble in dichloromethane. Therefore, if the dichloromethane is completely removed, both compounds would be left behind, making it difficult to separate them effectively through rechrystallization.
To separate the mixture of benzoic acid and acetanilide more effectively, a suitable technique would be acid-base extraction. Here's a brief explanation of the process:
1. Add a basic solution, such as sodium hydroxide, to the mixture. Benzoic acid will react with the base to form water-soluble sodium benzoate, while acetanilide will remain unchanged.
2. Shake the mixture to allow for thorough mixing. This will ensure that both compounds come in contact with the base.
3. After shaking, allow the mixture to settle. The water-soluble sodium benzoate will be present in the aqueous (water) layer, while acetanilide will remain in the organic (dichloromethane) layer.
4. Carefully separate the two layers by using a separatory funnel or by decanting. The aqueous layer containing sodium benzoate can be acidified to regenerate benzoic acid, which can then be recovered by filtration or rechrystallization. Acetanilide can be obtained from the organic layer by evaporating the solvent.
By using acid-base extraction instead of distillation and rechrystallization, it is possible to separate and recover both benzoic acid and acetanilide effectively from the mixture.