Part A

Question

The solutions in the two arms of a U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal.

A U-shaped tube is shown with a water-permeable membrane at the center of the bottom of the U-segment. The left side, labeled A, is filled with a mixture of 2 M sucrose and 1 M glucose. The right side, labeled B, is filled with a mixture of 1 M sucrose and 2 M glucose. The two sides of the tube are at the same level.

Which of the following is the most likely result when the system has reached equilibrium?

The concentration of sucrose on side A will be greater than the concentration of sucrose on side B.
The water level will be higher in side A than in side B.
The water level will be higher in side B than in side A.
The water levels will be unchanged.

Answer 1

To determine the final state of the system when it reaches equilibrium, we need to consider the movement of water across the membrane due to osmotic pressure.

Initial conditions:

• Side A: 2 M sucrose and 1 M glucose
• Side B: 1 M sucrose and 2 M glucose

The membrane is permeable to water and glucose but not to sucrose. Therefore, we need to analyze the concentrations of solutes that affect osmotic movement (i.e., sucrose since it cannot cross the membrane).

Osmotic pressure consideration:

• On side A, there are 2 M of sucrose, which creates a strong osmotic pressure, pulling water into that side.
• On side B, there is only 1 M of sucrose, which creates a lower osmotic pressure compared to side A.

As the sucrose cannot pass through the membrane, the concentration of free solute particles on each side determines the direction of water movement. The combination of solutes affects the water levels based on the effective osmolarity (the total concentration of solute particles that can create an osmotic effect).

• Side A has 2 M sucrose, which contributes significantly to osmotic pressure.
• Side B has only 1 M sucrose.

Even though there is more glucose on Side B, glucose can pass through the membrane, and it does not contribute to the osmotic pressure difference between the two sides.

Conclusion: Because sucrose on Side A creates a greater osmotic pressure than on Side B, water will move from Side B to Side A to balance the osmotic pressures.

Thus, the water level will be higher in side A than in side B when equilibrium is reached.

The correct answer is: The water level will be higher in side A than in side B.