Question

A \(10 \%(\mathrm{~m} / \mathrm{v})\) starch solution is separated from a \(1 \%(\mathrm{~m} / \mathrm{v})\) starch solution by a semipermeable membrane. (Starch is a colloid.) a. Which compartment has the higher osmotic pressure? b. In which direction will water flow initially? c. In which compartment will the volume level rise?

Short answer

a. 10% solution has higher osmotic pressure. b. Water flows from 1% to 10% solution. c. The volume level rises in the 10% solution compartment.

Step-by-step solution

- Determine Osmotic Pressure

Osmotic pressure is directly proportional to the concentration of the solute. Here, the higher concentration of starch is in the 10% solution compared to the 1% solution. Hence, the 10% starch solution has a higher osmotic pressure.

- Identify Initial Water Flow Direction

Water will naturally move from the area of lower solute concentration to the area of higher solute concentration. Therefore, water will flow from the 1% starch solution compartment to the 10% starch solution compartment.

- Predict Volume Level Change

With water flowing into the compartment with the 10% starch solution, the volume in this compartment will increase. Consequently, the volume level of the 10% starch solution compartment will rise.

Key concepts

Osmotic Pressure

Osmotic pressure is the pressure required to stop the flow of water across a semipermeable membrane. Osmotic pressure depends directly on the concentration of solutes in a solution. Higher solute concentration means higher osmotic pressure.

In our exercise, we have a 10% starch solution and a 1% starch solution separated by a semipermeable membrane. Since the 10% starch solution has a higher concentration of solute particles, it also has a higher osmotic pressure compared to the 1% starch solution.

Semipermeable Membrane

A semipermeable membrane is a barrier that allows certain molecules or ions to pass through it by diffusion. Typically, it permits the passage of solvent molecules but not larger solute molecules.

In osmosis, water moves through the semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. In our example, this membrane separates the 10% starch solution from the 1% starch solution, allowing water molecules to move while retaining the starch particles.

Solute Concentration

Solute concentration refers to the amount of solute present in a given quantity of solvent. It influences osmotic pressure and the direction of water flow.

In the exercise example, the 10% starch solution has a higher solute concentration compared to the 1% starch solution. Higher solute concentration in a solution means more particles that can attract water to balance the concentration differences.

Water Flow Direction

Water flow direction in osmosis is from the area with a lower solute concentration to an area with a higher solute concentration. This movement occurs to equalize solute concentrations on both sides of the semipermeable membrane.

In our example, water will move from the 1% starch solution (lower solute concentration) to the 10% starch solution (higher solute concentration). This movement also corresponds to the direction where the water potential is the highest to where it is the lowest.

Volume Change

Volume change in compartments separated by a semipermeable membrane is a result of water flow during osmosis. The compartment that receives more water will see an increase in volume, while the other compartment will see a decrease.

In the exercise, the 10% starch solution compartment will experience a rise in volume as water flows into it from the 1% starch solution compartment. Consequently, the 1% starch solution compartment will see a decrease in its volume level.