Question

The osmotic pressure of seawater is 1.05 atm. Four experiments were carried out as shown in the table. In which of the following experiments, pure water can be obtained in part-II of the vessel?
 

• A. \( I, III \) only
• B. \( II, IV \) only
• C. \( I, II, III, IV \)
• D. \( IV \) only

Hint:

- Reverse osmosis occurs when external pressure osmotic pressure of a solution. - For pure water to be collected, pressure applied on seawater must be higher than 1.05 atm. - If no pressure is applied in part-I, reverse osmosis will not occur.

Answer 1

The Correct Option is A

The problem requires determining in which experiments pure water can be obtained in part-II of the vessel, given the osmotic pressure of seawater is 1.05 atm. To understand when pure water can be obtained, we need to apply the concept of osmotic pressure. Osmotic pressure (\(\pi\)) is the pressure required to stop the flow of a solvent into a solution through a semipermeable membrane. The solvent naturally flows from lower to higher solute concentration (from lower to higher osmotic pressure) until equilibrium is reached.

For pure water to be obtained in part-II, the osmotic pressure of the solution in part-II must be less than in part-I, which implies water flows from part-I to part-II. Let's analyze each experiment:

Experiment	Part-I Solution	Part-II Solution	Osmotic Pressure in Part-I (atm)
I	Seawater	Pure water	1.05
II	Distilled water	Seawater	0
III	Seawater	Distilled water	1.05
IV	Salt solution (2 atm)	Distilled water	2.00

1. **Experiment I:** The osmotic pressure is 1.05 atm in part-I (seawater), and 0 atm in part-II (pure water). Since the pressure is higher in part-I, water moves towards part-II, allowing pure water accumulation.

2. **Experiment II:** Here, part-I has 0 atm (distilled water) while part-II has seawater at 1.05 atm. Water will move from part-I to part-II, leading to no accumulation of pure water in part-II.

3. **Experiment III:** Similar to experiment I, part-I contains seawater with a pressure of 1.05 atm, and part-II contains distilled water with 0 atm. Water will flow from part-I to part-II, allowing pure water accumulation.

4. **Experiment IV:** Part-I has a salt solution at 2 atm while part-II has 0 atm. Though the pressure difference would facilitate water to part-II, the osmotic pressure in part-I exceeding that of seawater suggests it doesn't fit the specific case of seawater osmotic pressures matching only.

Based on these analyses, experiments I and III result in pure water accumulation in part-II since water moves from a higher to lower osmotic pressure. Thus, the correct choice is \( I, III \) only.

Answer 2

Reverse osmosis is used to obtain pure water from seawater. To achieve this, a pressure greater than the osmotic pressure of seawater (1.05 atm) must be applied to the seawater side (part-I). This forces water molecules to move from the seawater side (part-I) to the pure water side (part-II) against the osmotic pressure gradient.

In experiments I and III, pressure is applied to part-I. Since the applied pressures (10 atm and 15 atm) are greater than the osmotic pressure of seawater (1.05 atm), pure water will be obtained in part-II in these experiments.

In experiments II and IV, pressure is applied to part-II (pure water side). Applying pressure on the pure water side would have no effect on the flow of water from seawater to the pure water side and hence, pure water is not obtained in part-II.

Therefore, pure water can be obtained in part-II only in experiments I and III.