Mass Transfer - Engineering

Q1:

In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.

A The entire amount of C is transferred to solvent B.

B Less than 2 kg but more than 1 kg of C is transferred to solvent B.

C Less than 1 kg of C is transferred to B.

D No amount of C is tranferred to B.

ANS:A - The entire amount of C is transferred to solvent B.

To solve this problem, we can use the equilibrium relationship provided: š‘Œ∗=0.9š‘‹Y∗=0.9X, where š‘Œ∗Y∗ is the concentration of C in solvent B (kg of C/kg of B) and š‘‹X is the concentration of C in solvent A (kg of C/kg of A). Initially, there are 2 kg of solute C in solvent A, and the total amount of solvent A is 8 kg. So, the initial concentration of C in solvent A is: š‘‹=2 kg8 kg=0.25 kg/kgX=8 kg2 kg​=0.25 kg/kg Now, using the equilibrium relationship š‘Œ∗=0.9š‘‹Y∗=0.9X, we can find the concentration of C in solvent B: š‘Œ∗=0.9×0.25=0.225 kg/kgY∗=0.9×0.25=0.225 kg/kg At equilibrium, the total amount of solute C transferred to solvent B will depend on the final concentration of C in solvent B. Now, let's analyze the answer choices:

  1. The entire amount of C is transferred to solvent B. - This is not likely, as the equilibrium relationship suggests that only a fraction of C will transfer to solvent B.
  2. Less than 2 kg but more than 1 kg of C is transferred to solvent B. - This seems plausible, as the concentration of C in solvent B is less than the concentration in solvent A, indicating some transfer but not the entire amount.
  3. Less than 1 kg of C is transferred to B. - This is not likely, as the equilibrium relationship indicates that a significant fraction of C will transfer to solvent B.
  4. No amount of C is transferred to B. - This is not likely, as there is a solute-solvent interaction, and the equilibrium relationship suggests some transfer of C to solvent B.
So, the correct answer is: Less than 2 kg but more than 1 kg of C is transferred to solvent B. 2 / 2