Extraction of caffeine:
You had extracted 2 g of crude caffeine and you were in a hurry. Instead of doing the 6 successive extractions with 2ml portions of methylene chloride, you only did 2 successive extractions with 6 ml portions of solvent. Now, calculate the total mass of pure caffeine recovered in these 2 operations.
To calculate the total mass of pure caffeine recovered in the two operations, we need to consider the percent recovery for each individual extraction and then add them together.
First, let's calculate the percent recovery for each extraction. The percent recovery is calculated by dividing the mass of the recovered caffeine by the mass of the initial crude caffeine, and then multiplying by 100.
In the original procedure, we performed 6 successive extractions with 2 ml portions of methylene chloride. Since each extraction is done with 2 ml, and we performed 2 extractions with 6 ml portions, the total volume of solvent used is 2 ml * 2 + 6 ml * 2 = 16 ml.
Now, let's calculate the percent recovery for each extraction:
Extraction 1:
Mass of recovered caffeine = 2 g / 16 ml * 2 ml = 0.25 g
Percent recovery for extraction 1 = (0.25 g / 2 g) * 100 = 12.5%
Extraction 2:
Mass of recovered caffeine = 2 g / 16 ml * 6 ml = 0.75 g
Percent recovery for extraction 2 = (0.75 g / 2 g) * 100 = 37.5%
Next, we add the individual percent recoveries to get the total percent recovery:
Total percent recovery = Percent recovery for extraction 1 + Percent recovery for extraction 2
Total percent recovery = 12.5% + 37.5% = 50%
Finally, we calculate the total mass of pure caffeine recovered:
Total mass of pure caffeine recovered = Total percent recovery * Initial mass of crude caffeine
Total mass of pure caffeine recovered = 50% * 2 g = 1 g
Therefore, the total mass of pure caffeine recovered in these 2 operations is 1 gram.