the solubility of a compound is 59g per 100 mL in boiling methanol and 30g per 100mL in cold methanol, whereas its solubility in water is 7.2g per 100 mL at 95 C and .22g per 100mL at 2C. Which solvent would be better for recrystallization of the compound? Explain.
Well this is my take on this. I calculated the recovery yeild of each and I get 49% for the first ans 90% something for the second. I pick the second solvent to be better because it produces a higher recovery rate. However, I am a bit confused I'm I right. Is this good reasoning?
I don't see anything wrong with your reasoning. However, there are other things to consider than gross solubility; e.g., ease of dissolving, the impurity which one is trying to eliminate,etc. Based on the problem, with just solubility and no impurity listed, the loss of the ingredient in methanol is high.
Thank you. i understand this now.
Your reasoning is partly correct, but it is not the only factor to consider when determining the better solvent for recrystallization. In addition to the recovery yield, factors such as solubility, purity, and the desired characteristics of the crystal also need to be considered.
In selecting a solvent for recrystallization, the goal is to choose a solvent in which the compound is highly soluble at high temperature, but significantly less soluble at low temperature. This allows the compound to dissolve at high temperature and then recrystallize as the solvent cools down, leading to the formation of pure crystals.
Based on the solubility data provided, it can be observed that the compound has a high solubility in boiling methanol (59g/100mL) and a low solubility in cold methanol (30g/100mL). This indicates that methanol is a suitable solvent for recrystallization.
On the other hand, the solubility of the compound in water is relatively low at both high temperature (7.2g/100mL at 95°C) and low temperature (0.22g/100mL at 2°C). This suggests that water might not be an ideal solvent for recrystallization.
In summary, based on the given data, it is reasonable to conclude that boiling methanol would be a better solvent for the recrystallization of the compound due to its higher solubility at high temperature and lower solubility at low temperature. However, recovery yield alone is not sufficient to determine the suitability of a solvent for recrystallization. Other factors like purity, ease of separation, and desired crystal characteristics should also be taken into account.
Your reasoning is partially correct, but there are a few more factors to consider when determining which solvent would be better for recrystallization.
One important factor is the solubility of the compound in the respective solvents. In the case of recrystallization, you want the compound to dissolve as little as possible at low temperatures, so that it can easily be separated from impurities by filtration during the recrystallization process.
Based on the given solubility data, the compound has a significantly lower solubility in water (0.22g per 100 mL at 2°C) compared to cold methanol (30g per 100 mL). This suggests that water is a better solvent for recrystallization because the compound will remain largely insoluble and readily precipitate out of solution at low temperatures.
Additionally, the recovery yield alone might not be the sole determining factor for selecting the recrystallization solvent. Other factors such as the compound's stability, ease of filtration, and safety considerations should also be taken into account. However, since you did not mention any other relevant details, we'll focus on solubility alone for this analysis.
In conclusion, based on the given solubility data, water would be a better solvent for recrystallization of the compound because it has lower solubility at the desired lower temperatures, allowing for easy separation of the compound from impurities.