Question

Which of the following is a colligative property? (a) Molecular weight (b) Osmotic pressure (c) Parachor (d) Surface tension

Short answer

Out of the given options, Osmotic pressure (b) is a colligative property.

Step-by-step solution

Analyze all options

Each option should be analyzed individually. Molecular weight is not a colligative property, it is the weight of a molecule and is used in stoichiometry. Parachor is a property related to the surface tension of a liquid and its specific volume. Surface tension itself is a property of liquids that arises due to forces of attraction between the liquid molecules, preventing the liquid from being easily pulled apart.

Identify the colligative property

Osmotic pressure is a colligative property. It is the pressure required to prevent solvent from passing into a given solution by osmosis. Osmotic pressure, like other colligative properties, depends on the number of solute particles dissolved in the solvent, not on the nature of the particles.

Key concepts

Osmotic Pressure

Osmotic pressure is a fascinating colligative property that plays a crucial role in various biological and chemical processes. It results from the movement of solvent molecules through a semi-permeable membrane from a dilute solution to a more concentrated one. This process is known as osmosis.

The pressure needed to stop this flow of solvent is known as osmotic pressure. It depends on the concentration of solute particles in the solution. Unlike other properties, it does not depend on the type of molecules that make up the solute, but rather the number of particles involved. This is a characteristic feature of colligative properties.

• Formula: Osmotic pressure (\( \Pi \)) is calculated using Van't Hoff's equation: \( \Pi = iCRT \). Here, i is the van't Hoff factor, C is the molar concentration of the solute, R is the ideal gas constant, and T is the temperature in Kelvin.
• It has important applications in fields such as biology, where it explains cellular behavior, and medicine, particularly in understanding how intravenous fluids work.

Molecular Weight

Unlike osmotic pressure, molecular weight is not considered a colligative property because it is a measure of the amount of matter in a substance. It is the sum of the atomic masses of all the atoms in a molecule and is typically expressed in atomic mass units (amu).

Molecular weight is essential in stoichiometry as it allows chemists to calculate the amounts of reactants and products involved in a chemical reaction. Knowing the molecular weight helps in understanding how much of a substance is involved in a reaction, which is crucial for practical laboratory work.

• Applications: Used to convert moles to grams in chemical equations, it is fundamental for preparing solutions with precise concentrations.
• It guides the determination of the correct proportions of reactants needed for a desired product yield.

Surface Tension

Surface tension is a unique property that describes how molecules at the surface of a liquid behave differently compared to those in the bulk. This is due to the cohesive forces between liquid molecules.

At the surface, molecules experience a net inward force because they are only attracted by neighbors below and to the side, creating a "film" on the surface. This tension allows objects with high buoyancy, like water striders, to "walk" on water without sinking.

• Influencing Factors: Temperature is a significant factor affecting surface tension. As temperature increases, surface tension decreases since molecules move apart more freely.
• Surface tension is not a colligative property, as it depends on the specific molecular interactions and strengths of the cohesive forces within the liquid.
• Applications: Surface tension is pivotal in industries such as inkjet printing, detergents manufacturing, and in the pharmaceutical industry for drug formulations.