A student dissolved 30 mg of a crude unknown in 2 ml of 95% ethanol at room temperature. After chilling in an ice bath and washing crystal with small amount of ice-cold ethanol, she recovered 5mg. Why was the recovery so low?
1) solubility in cold ethanol is higher than expected.
A. Too soluble in ethanol.
B. The sample was VERY crude (not much of the compound to start with).
The low recovery of the crude unknown can be attributed to several factors. Here are a few possibilities:
1. Solubility: The low recovery could be due to the unknown compound having a low solubility in the solvent used (95% ethanol). If the compound is not very soluble, it may not fully dissolve in the solvent, leading to a low recovery.
2. Impurities: The presence of impurities in the crude unknown can also result in a low recovery. These impurities could be insoluble in the solvent or could interfere with the crystallization process, preventing the compound from completely separating and being recovered.
3. Loss during washing: During the washing step with ice-cold ethanol, some of the compound may have been lost. This can happen if the compound is not well adhered to the crystal or if it is washed away by the solvent.
4. Incomplete crystallization: If the compound did not fully crystallize during the cooling process in the ice bath, the recovery would be low. This could happen if the cooling conditions were not optimal or if the compound has a tendency to form amorphous or oil-like substances instead of well-defined crystals.
It is important to note that without additional information or experimental details, it is difficult to determine the exact reason for the low recovery. Further analysis and experimentation may be necessary to identify the specific factors affecting the recovery of the crude unknown.