chloroform is an excellent solvent for extraction caffeine from water. Kd = 10 for caffeine in chloroform- water at 25 Celsius. what weight of caffeine would be removed from a solution of 4g caffeine in 100ml water by a single extraction of 100 ml of chloroform?
for the situation in the uestion above, what total weight of caffeine could be rmoved by two extractions using 50 ml of chloroform each time?
K(org/aq) = (grams/org solvent)/(g/aq solvent)
10 = (x grams/100 mL)/(4-x grams/100 mL)
Solve for x, then calculate 4-x to determine the amount left in the aqueous phase.
To calculate how much caffeine would be removed by a single extraction of 100 ml chloroform, we need to use the distribution coefficient (Kd) and the initial concentration of caffeine.
1. Determine the amount of caffeine extracted in a single extraction:
Kd = Caffeine in chloroform / Caffeine in water
Kd = 10
Let's assume x represents the amount of caffeine extracted into the chloroform layer in grams.
Caffeine in chloroform = x grams
Caffeine in water = (4 - x) grams (initial concentration minus extracted amount)
Applying the formula for Kd:
10 = x / (4 - x)
Solving this equation, we find that x ≈ 0.444 grams.
Therefore, a single extraction of 100 ml chloroform would remove approximately 0.444 grams of caffeine.
Now, let's calculate the total weight of caffeine that could be removed by two extractions using 50 ml of chloroform each time.
2. Determine the amount of caffeine extracted in the first extraction:
Apply the same logic as in the previous step, but with 50 ml chloroform:
Kd = x / (4 - x)
10 = x / (4 - x)
Solving this equation, we find that x ≈ 0.222 grams.
For the first extraction, approximately 0.222 grams of caffeine would be removed.
3. Determine the amount of caffeine remaining after the first extraction:
Caffeine remaining in water = 4 - 0.222 grams = 3.778 grams
4. Determine the amount of caffeine extracted in the second extraction:
Repeat the steps from the first extraction with the remaining caffeine in water (3.778 grams) and 50 ml chloroform:
Kd = x / (3.778 - x)
10 = x / (3.778 - x)
Solving this equation, we find that x ≈ 0.186 grams.
For the second extraction, approximately 0.186 grams of caffeine would be removed.
5. Calculate the total weight of caffeine removed in both extractions:
Total weight = 0.222 grams (first extraction) + 0.186 grams (second extraction)
Total weight ≈ 0.408 grams
Therefore, a total of approximately 0.408 grams of caffeine could be removed by two extractions using 50 ml of chloroform each time.
To solve this problem, we need to use the concept of partition coefficient (Kd) and the formula for extraction.
The partition coefficient (Kd) is a measure of how much a substance prefers one phase (in this case, chloroform) over another phase (in this case, water). It is defined as the ratio of the concentration of the solute in the two phases at equilibrium.
In the given problem, the Kd of caffeine in chloroform-water is given as 10. This means that caffeine is 10 times more soluble in chloroform than in water.
To calculate the weight of caffeine removed from a solution, we need to determine how much caffeine is transferred from water to chloroform during extraction.
1. For the first extraction:
- We have 4g of caffeine in 100ml water.
- We extract 100ml of chloroform.
- Since the Kd value is 10, this means that for every 1g of caffeine in water, 10g of caffeine will be extracted into chloroform.
- Therefore, the weight of caffeine extracted in the first extraction can be calculated using the ratio: (100ml chloroform / 100ml water) * (4g caffeine) * (10) = 40g of caffeine.
So, 40g of caffeine will be removed from the solution during the first extraction.
2. For the second extraction:
- The remaining solution after the first extraction contains 4g - 40g = 36g of caffeine.
- We extract 50ml (half of the previous volume) of chloroform.
- Using the same concept, since Kd = 10, for every 1g of caffeine in water, 10g of caffeine will be extracted into chloroform.
- Therefore, the weight of caffeine extracted in the second extraction can be calculated using the ratio: (50ml chloroform / 100ml water) * (36g caffeine) * (10) = 18g of caffeine.
So, 18g of caffeine will be removed from the solution during the second extraction.
To calculate the total weight of caffeine removed by two extractions, we add the caffeine extracted in each extraction:
40g + 18g = 58g
Therefore, the total weight of caffeine that could be removed by two extractions using 50ml of chloroform each time is 58g.