Problem 7 - A Complete Resource Book in Chemistry for JEE Main

Question

During osmosis, flow of water through a semipermeable membrane is (a) from both sides of semi-permeable membrane with unequal flow rates (b) from solution having lower concentration only (c) from solution having higher concentration only (d) from both sides of semi-permeable membrane with equal flow rates

Step-by-Step Solution

Answer

The correct option is (b).

Step 1: Understand Osmosis

Osmosis is the movement of water molecules from a region of lower solute concentration to a region of higher solute concentration through a semi-permeable membrane. It aims to equalize solute concentrations on the two sides of the membrane.

Step 2: Evaluate Option (a)

Option (a) suggests water flows from both sides with unequal rates. However, osmosis is characterized by the net movement of water molecules from the less concentrated solution to the more concentrated solution, not from both directions equally.

Step 3: Evaluate Option (b)

Option (b) suggests water flows from a lower concentration solution. This aligns with osmosis, where water moves from low solute concentration (more water) to high solute concentration (less water) to balance concentrations.

Step 4: Evaluate Option (c)

Option (c) suggests water flows from a higher concentration. This contradicts osmosis because water does not typically move from a higher solute concentration area; rather, it flows toward it to dilute the solute concentration.

Step 5: Evaluate Option (d)

Option (d) suggests flow from both sides with equal rates, contradicting osmosis which involves net flow in one direction, from low to high solute concentration. Equal rates cancel each other's effects.

Step 6: Choose the Correct Answer

Based on the understanding of osmosis, the correct choice aligns with water moving from a region of lower solute concentration to higher solute concentration. Hence, the correct option is (b).

Key Concepts

Semi-permeable membrane

A semi-permeable membrane is a type of biological or synthetic barrier that allows some molecules to pass through while blocking others. This selective permeability is crucial in the process of osmosis. In biological systems, cell membranes are naturally semi-permeable, allowing water molecules to move across while preventing larger solute molecules from doing so. This selective nature is what enables osmosis to work effectively and helps maintain cellular balance.

Think of it like a tight weave in a fabric. It lets water pass but blocks bigger particles, much like how a strainer lets water through but stops pasta from falling out. Without semi-permeable membranes, cells couldn't regulate their internal environment, which would disrupt vital processes and potentially harm the cell.

Solute concentration

Solute concentration refers to the amount of solute present in a solution. In the context of osmosis, it's all about comparing the concentration of solutes on either side of a semi-permeable membrane.

A region with higher solute concentration means there are more solute particles and less water. Conversely, a lower solute concentration means fewer solute particles and more water.

• High solute concentration: More solutes, less water.
• Low solute concentration: Fewer solutes, more water.

Understanding this balance is essential because osmosis is driven by the difference in water potential created by these varying concentrations. The natural tendency is for water to move from areas with plenty of it (low solute concentration) to areas where it's needed more (high solute concentration).

Water movement

Water movement during osmosis is driven by the concentration gradient, moving from an area of low solute concentration – where there is more water – to an area of high solute concentration – where there is less water.

This movement is crucial because it helps balance solute concentrations between two solutions separated by a semi-permeable membrane. By doing so, water molecules move to where they are needed most, facilitating important biological processes such as nutrient absorption, waste removal, and maintaining cell turgor pressure.

It's similar to filling an empty cup with water from a full one until both are equally full. Osmosis seeks to reach equilibrium by adjusting water amounts across a membrane.

Net flow direction

The net flow direction in osmosis is determined by differences in solute concentration across a semi-permeable membrane. It describes the overall movement of water molecules, which is always from a region of low solute concentration to a region of high solute concentration.

This "one-way street" flow of water is what differentiates osmosis from simple diffusion, which can occur in any direction. In an osmosis scenario, water moves specifically to balance the solute concentrations on both sides of the membrane.

Understanding net flow is important because it highlights the direction of water movement, helping in processes like the hydration of cells and transportation of nutrients. In practical terms, it's like how people move from a crowded area to a less crowded one to create equal space.