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Diclofenac is a non-steroidal anti-inflammatory drug. if the water discharge of your diclofenac manufacturing facility contains 5.0 g/l diclofenac and you wish to remove 99.0% of the drug from 100 l wastewater using n-octane, how many liquid-liquid extraction should be done if you will use 50 l for each extraction? (ko=25.0) a) only 1 b) at least 2 c) at least 3 d) at least 4
Accepted Answer
Here's how to solve this problem using liquid-liquid extraction principles:
Understanding the Concept
Liquid-liquid extraction relies on the difference in solubility of a solute (in this case, diclofenac) between two immiscible solvents (water and n-octane). The distribution coefficient (Kd) quantifies this difference, with a higher Kd indicating a preference for the organic solvent (n-octane).
Calculations
1. Initial Mass of Diclofenac:
Concentration = 5.0 g/L
Volume = 100 L
Initial Mass = Concentration
Volume = 5.0 g/L
100 L = 500 g
2. Desired Removal:
99% removal means 1% remaining.
Final mass = 1% of initial mass = 0.01
500 g = 5 g
3. Single Extraction Calculation:
Let 'x' be the mass of diclofenac remaining in the water after one extraction.
Kd = [diclofenac in n-octane] / [diclofenac in water] = (500 - x) / x = 25.0
Solving for x, we get x ≈ 19.6 g
4. Multiple Extractions:
Since the initial mass is 500 g and we need to reduce it to 5 g, we need to perform multiple extractions.
After one extraction: 19.6 g remains.
After two extractions: We repeat the calculation with 19.6 g as the initial mass, and we'll find that the remaining mass will be significantly less than 5 g.
Conclusion
Therefore, at least two liquid-liquid extractions are required to remove 99% of diclofenac from the wastewater. So the answer is B) at least 2.
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