AP Biology - Osmosis

Question

A scientist has set up 2 different U-shaped tubes filled with water. NaCl is dropped in one side of each tube where KCl is dropped in the other side for both, at the bottom of each tube is a semipermeable membrane. One tube is only permeable to Cl- ions while the other tube is only permeable to K+ ions. Assuming equal initial molarities for both sides, describe and explain the final conditions for each tube.

Answer 1

Tube Permeable to Cl- Ions:

1. NaCl side:
2. NaCl dissociates into Na+ and Cl- ions. Since the tube is permeable to Cl- ions, they can move through the membrane.
3. Cl- ions will move from the NaCl side to the other side, equalizing the concentrations of Cl- ions.
4. KCl side:
5. KCl dissociates into K+ and Cl- ions. The Cl- ions cannot pass through the membrane.
6. Cl- ions will remain on the KCl side, leading to a higher concentration of Cl- ions on this side compared to the NaCl side.

Final condition:

1. The side where NaCl was added will have equal concentrations of Na+ and Cl- ions due to Cl- ion movement across the semipermeable membrane.
2. The side where KCl was added will have a higher concentration of Cl- ions due to the inability of Cl- ions to move through the membrane.

Tube Permeable to K+ Ions:

1. NaCl side:
2. NaCl dissociates into Na+ and Cl- ions. Na+ ions cannot pass through the membrane.
3. Cl- ions will move from the NaCl side to the other side, leading to a higher concentration of Cl- ions on this side.
4. KCl side:
5. KCl dissociates into K+ and Cl- ions. K+ ions will move through the membrane.
6. K+ ions will move from the KCl side to the NaCl side, equalizing the concentrations of K+ ions.

Final condition:

1. The side where NaCl was added will have a higher concentration of Cl- ions due to Cl- ion movement across the semipermeable membrane.
2. The side where KCl was added will have equal concentrations of K+ and Cl- ions due to K+ ion movement across the semipermeable membrane