what could be possible answers to these two questions.....1 why determine the amount of solvent by difference and not by weighing the final distillate?????
why not distill off all the solvent at the very beginnig and then separate the solid residue of benzoic acid and benzoin recrystallisation
One almost ALWAYS weighs by difference (ALWAYS if you're in quant lab--perhaps not so often in other course where you can scoot by with a little less precision and accuracy)l Let me exaggerate with an example.
Let's suppose we want to weigh a sample for analysis. We place some powder on the pan and it weighs 2.00 g + 1.00 g = 3.00 grams. So we record a mass of 3.00 g in out lab book. (And your instructor chews on you for placing a sample directly on the pan but play along with me here). Now, what you don't know is that the weights are not calibrated properly. The 1.00 g weight actually has a mass of 1.00 grams; the 2.00 grams weight actually has a mass of 1.00 g. So the sample we just weighed has a real mass of 2.00 grams but we've recorded it as 3.00 grams. We are in big trouble already.
Suppose we weigh the sample by difference.
First we weigh a sample with container. We use the 1.00 g weight (that is accurate) and the 2.00 gram weight (which actually weighs 1.00 g) and a 5.00 gram weight that is accurate. The total mess weighs (we think) 1 + 2 + 5 = 8.00 g. Next we pour out some of the sample and weigh again. This time it weighs 2.00 (which actually weighs 1.00 but it is calibrated as 2.00) + 5.00 so we record it as 7.00 g. Weighing by difference gives us 8.00-7.00= 1.00 g (EVEN though we used the miscalibrated weight). The safe thing to do is weigh by difference. Errors in handling, calibration, etc, tend to cancel.
Why not distill to bone dry (or near bond dry) conditions. The organic materials will likely decompose at elevated temperature.
1. Why determine the amount of solvent by difference and not by weighing the final distillate?
Possible answers could include:
- Determining the amount of solvent by difference is a more accurate way to measure the amount of solvent used in a solution. This method involves measuring the initial mass of the solvent and subtracting the mass of the solute after evaporation. It takes into account any evaporation or loss of solvent during the process.
- Weighing the final distillate may not accurately represent the amount of solvent used. This is because the distillation process involves the separation of different components, and some of the solvent may be lost or evaporated during the distillation, leading to an inaccurate measurement.
2. Why not distill off all the solvent at the very beginning and then separate the solid residue of benzoic acid and benzoin recrystallization?
Possible answers could include:
- Distilling off all the solvent at the beginning and then separating the solid residue can lead to loss or contamination of the desired compounds. Some compounds may have volatile components that can be lost during distillation, or the high temperature involved in distillation may compromise the integrity of the compounds.
- Separating the solid residue after recrystallization helps in purifying and isolating the desired compound. Recrystallization allows for the removal of impurities, resulting in a purer final product. By separating the solid residue, you can obtain higher-quality benzoic acid and benzoin compounds.