Reporting and Discussing Percent Yields
- Loss during transfers. Identify specifically the most problematic transfers involved in the procedures.
- Loss due to reaction inefficiency. Were there side reactions that wasted the limiting reactant? Was it a slow reaction, for which a longer reaction period was needed to achieve complete conversion of the limiting reactant? Was there an unfavorable equilibrium constant involved?
- Unavoidable losses during work up. Examples: In vacuum filtration steps usually the solid being filtered is slightly soluble in the solvent being used and so some of the solid stays dissolved in the liquid filtrate. Similar loss occurs during extraction steps if the desired compound has any water solubility (it dissolves into the aqueous layer). Distillation steps always involve loss due to the fact that not all material can be expected to distill out ("hold-up volume"). Drying over sodium sulfate usually involves a decantation step that unavoidably leaves behind some of the solution with the drying agent.
- Procedural mistakes, poor technique, or lab accidents. Of course, these can play a role, but this discussion should not be about beating yourself up or finding blame. If there was a mistake then, by all means, do note it and it is certainly fair to note that you are beginners and with practice you would probably be able to achieve a better percent yield. Do not use having made a mistake or accident as an out that gets you out of discussing more weighty reasons for lost yield.
