A student crystallized a compound from benzene and observed only a few crystals when the solution cooled to room temperature. To increase the yield of crystals, the students chilled the mixture in an ice-water bath. The chilling greatly increased the quantity of solid material in the flask. Yet when the student vacuum filtered these crystals, only a few crystals remained on the filter paper. Explain what this student might have done wrong to obtain this outcome
The vapor pressure of the solid may have been high and the vacuum filtration simply sublimed much of the solid.
more charcoal might be added
Based on the given scenario, there are a few possible explanations for why only a few crystals remained on the filter paper after vacuum filtration. The student might have made some mistakes during the process that led to this outcome. Here are a few potential reasons:
1. Inadequate cooling: The student may not have adequately chilled the mixture in the ice-water bath. Cooling the solution helps in promoting crystal formation. If the temperature was not low enough or the mixture was not chilled for a sufficient amount of time, it could have resulted in a lower yield of crystals.
2. Insufficient drying: After filtering the crystals, the student might not have properly dried them. Moisture content can cause crystals to be less stable and more prone to dissolve or disintegrate during the filtration process. It is important to thoroughly dry the crystals to ensure their stability and prevent loss during filtration.
3. Inappropriate filtration technique: The student might have used an unsuitable filter paper or filter setup for the given compound. Different substances require different filtration methods, such as using a specific filter paper or adjusting the vacuum pressure. If the filter paper used was not suitable for the compound or if the vacuum filtration setup was not correctly adjusted, it could have resulted in poor crystal retention.
4. Insufficient washing: Washing the crystals after filtration is crucial to remove impurities or residual solvent. If the student did not wash the crystals adequately, some of the impurities might have remained on the filter paper, resulting in fewer crystals being obtained.
To improve the yield of crystals and obtain a better outcome, the student should consider the following steps:
1. Ensure proper cooling: Make sure to sufficiently cool the mixture in the ice-water bath. Consider using a thermometer to monitor the temperature and give it enough time to reach the desired temperature.
2. Thoroughly dry the crystals: After filtration, allow enough time for the crystals to dry completely. This can be done by placing them in an oven or desiccator to remove any remaining moisture.
3. Use appropriate filter paper and filtration setup: Select a filter paper suitable for the compound being filtered and adjust the vacuum pressure accordingly. Make sure to use a filter paper that is capable of retaining crystals of the desired size.
4. Ensure proper washing: Wash the crystals with an appropriate solvent to remove impurities and residual solvents. This step helps improve the purity of the crystals and increases the yield.
By following these steps and taking care to address the potential mistakes mentioned, the student should have a better chance of obtaining a higher yield of crystals during vacuum filtration.