Question

A semipermeable membrane used in the measurement of osmotic pressure of a solution allows the passage of: (a) solute molecules through it (b) solvent molecules through it (c) both solvent and solute molecules (d) either solvent or solute

Short answer

The correct answer is (b) solvent molecules through it, as semipermeable membranes in osmosis allow only the solvent to pass through.

Step-by-step solution

Understanding Semipermeable Membranes

A semipermeable membrane, often used in osmosis experiments, is a type of barrier that allows certain substances to pass through it while blocking others. In the context of osmosis, the membrane typically allows solvent molecules to pass through but not solute molecules.

Applying Definitions to Choices

We apply the definition of a semipermeable membrane to the given options. (a) Incorrect, as solute molecules cannot pass through. (b) Correct, as solvent molecules can pass through. (c) Incorrect, since it states both can pass, which contradicts the membrane's selectivity. (d) Incorrect, as it is non-specific and implies a variability not characteristic of such membranes.

Identifying the Correct Answer

Given the definition of a semipermeable membrane and the process of osmosis, we determine that the correct choice is the one that states only solvent molecules are allowed to pass through. From the options provided, that is option (b).

Key concepts

Osmotic Pressure

Osmotic pressure is a fundamental concept when studying movement across a semipermeable membrane. It’s the pressure required to prevent the flow of solvent molecules into a solution via osmosis. Imagine pouring fresh water on one side of a semipermeable membrane and saltwater on the other. The fresh water, which is the solvent, tries to dilute the saltwater by moving through the membrane. The osmotic pressure is what would be needed to stop this flow. It’s a vital factor in maintaining the balance of fluids in biological systems and is driven by the concentration of solute molecules. The greater the difference in concentration, the higher the osmotic pressure.

It’s similar to a crowded room where everyone wants to move to a less crowded space. The osmotic pressure would be like the force of the door that keeps everyone inside despite their push to spread out.

Solvent Molecules

Solvent molecules are the numerous, usually liquid, particles in a solution that dissolve the solute. Water is the most common solvent and is key to the process of osmosis. In osmosis, solvent molecules move across a semipermeable membrane to balance solute concentrations.

To picture this, think of a dry sponge representing the solvent molecules. When you plunge it into water, the sponge absorbs the water. In a similar way, solvent molecules can pass through a semipermeable membrane, absorbing and carrying with them any dissolved substances that are small enough to fit through the membrane pores.

Solute Molecules

Solute molecules are the minority in a solution, dissolved by the solvent. For instance, if you stir sugar into water, the sugar is the solute. Unlike solvent molecules, solute molecules typically cannot pass through a semipermeable membrane during osmosis. This is due to their size or chemical properties that don't align with the membrane's selective permeability.

Continuing with our previous analogy, the solute molecules are like the larger rocks that can’t be absorbed by the sponge. They remain behind when the solvent, or water, is absorbed through the semipermeable membrane.

Osmosis Experiments

Osmosis experiments are designed to observe and understand the osmotic movement of solvent molecules across a semipermeable membrane. These experiments often involve two solutions of different solute concentrations separated by a semipermeable membrane. Students can witness osmosis by observing the movement of the solvent from a lower solute concentration to a higher one until equilibrium is reached.

To create an osmosis experiment, one can use materials like dialysis tubing, which acts as the membrane, and solutions of varying concentrations. Through these experiments, we can explore physiological processes such as the kidneys’ function in filtering blood, where a semipermeable membrane allows certain substances to pass while retaining others.