Define the term osmotic pressure. What is the advantage of using osmotic pressure as compared to other colligative properties for the determination of molar masses of solutes in the solutions? Arrange the following solutions in increasing order of their osmotic pressure.

• A. 34.2 g/lt sucrose
• B. 60 g/lt of Urea
• C. 90 g/lt of glucose
• D. 58.5 g/lt of sodium chloride

Give the reason in support of your answer.

Osmotic pressure is a fundamental concept in chemistry that refers to the pressure required to stop the flow of solvent into a solution through a semipermeable membrane. This phenomenon occurs when two solutions of different concentrations are separated by a membrane that allows only solvent molecules to pass through. The solvent naturally moves from the area of lower solute concentration to the area of higher solute concentration, creating a pressure difference. This pressure difference is what we call osmotic pressure.

Understanding Osmotic Pressure

To grasp the significance of osmotic pressure, it's essential to recognize that it is a colligative property. Colligative properties depend on the number of solute particles in a solution rather than the identity of the solute. This means that osmotic pressure can provide valuable insights into the molar mass of solutes when measured accurately.

Advantages of Osmotic Pressure Measurement

Using osmotic pressure to determine molar masses has several advantages over other colligative properties, such as boiling point elevation or freezing point depression:

• Precision: Osmotic pressure measurements can be very precise, especially in dilute solutions, allowing for accurate calculations of molar mass.
• Wide Applicability: It can be applied to both ionic and non-ionic solutes, making it versatile for various types of substances.
• Minimal Interference: Unlike boiling point elevation or freezing point depression, osmotic pressure is less affected by impurities or the presence of multiple solutes.

Comparing Solutions by Osmotic Pressure

Now, let's arrange the given solutions in increasing order of their osmotic pressure. The solutions are:

• A. 34.2 g/L sucrose
• B. 60 g/L urea
• C. 90 g/L glucose
• D. 58.5 g/L sodium chloride

To determine the osmotic pressure, we need to consider the concentration of solute particles in each solution. For ionic compounds like sodium chloride, it dissociates into two ions (Na⁺ and Cl^-), effectively doubling the number of solute particles. In contrast, sucrose, urea, and glucose do not dissociate in solution.

Calculating Effective Concentrations

Let's calculate the effective concentration of solute particles for each solution:

• A. Sucrose: 34.2 g/L (1 particle)
• B. Urea: 60 g/L (1 particle)
• C. Glucose: 90 g/L (1 particle)
• D. Sodium Chloride: 58.5 g/L (2 particles, since it dissociates into Na⁺ and Cl^-)

Next, we need to convert these masses into molar concentrations:

• Sucrose (C₁₂H₂₂O₁₁): Molar mass ≈ 342 g/mol → 34.2 g/L = 0.1 mol/L
• Urea (NH₂CO): Molar mass ≈ 60 g/mol → 60 g/L = 1 mol/L
• Glucose (C₆H₁₂O₆): Molar mass ≈ 180 g/mol → 90 g/L = 0.5 mol/L
• Sodium Chloride (NaCl): Molar mass ≈ 58.5 g/mol → 58.5 g/L = 1 mol/L (but contributes 2 particles, so effective concentration = 2 mol/L)

Arranging by Osmotic Pressure

Now, we can arrange the solutions based on their effective concentrations:

• A. Sucrose: 0.1 mol/L
• C. Glucose: 0.5 mol/L
• B. Urea: 1 mol/L
• D. Sodium Chloride: 2 mol/L

Thus, the increasing order of osmotic pressure is:

1. A. 34.2 g/L sucrose
2. C. 90 g/L glucose
3. B. 60 g/L urea
4. D. 58.5 g/L sodium chloride

This arrangement is based on the effective concentration of solute particles, which directly influences the osmotic pressure of the solutions. The higher the concentration of solute particles, the greater the osmotic pressure.