W4-Colligative properties

14 Questions

What is an ideal solution?

A solution where there is no change in the properties of the components, other than dilution, when they are mixed

What does free energy quantitatively measure?

The escaping tendencies of material substances undergoing transformations

Which property serves as a quantitative expression of escaping tendency?

Vapour pressure of a solution

What does Raoult's law describe in relation to solutions?

The vapor pressure lowering in ideal solutions

What is the phenomenon described by Henry's law?

The solubility of gases in liquids is directly proportional to the partial pressure of that gas above the liquid

What is the formula for calculating the partial vapor pressure of a component in a solution according to Raoult's Law?

$P_A = X_A P_{0A}$

In which type of deviation from Raoult's law does the boiling point of a solution increase?

Negative deviation

What happens to the vapor pressure of a solvent when solute molecules are added to a solution?

Decreases

What formula can be used to calculate osmotic pressure for non-electrolyte solutions?

$pV = nRT$

What is the practical osmotic coefficient (Φ) in the context of electrolytes?

The deviation of the solution from ideality (activity coefficient)

How is the amount in moles of osmotically active species in solution expressed?

Osmolarity or osmolality

What happens to bacteria when exposed to strongly hypertonic solutions?

They are plasmolysed

Why is it important for eye medication to be isotonic?

To prevent damage to delicate membranes in the eye due to osmotic pressure

What is the relationship between two solutions that have the same osmotic pressure?

They are isoosmotic, or isotonic

Study Notes

Water molecules turn into vapor when the pressure applied on its surface is low. The opposite is also true: the higher the pressure, the harder it is for molecules to become vapor.
Raoult's Law: The vapor pressure of a solution is an expression of the escaping tendency of its volatile constituents. The partial vapor pressure of each component is equal to the vapor pressure of the pure constituent multiplied by its mole fraction in the solution. (PA = XAP₀A, PB = XBP₀B)
In an ideal solution, the vapor pressure of a constituent is reduced by dilution with another constituent in a manner that depends on their mole fractions.
CFCs (Chlorofluorocarbons) are used as propellants in MDIs (Metered Dose Inhalers) due to their suitable blends and intermediate vapor pressure.
Real solutions, also known as non-ideal solutions, exhibit adhesion forces between constituents that are stronger than the cohesion forces within the pure constituents. Such solutions do not follow Raoult's law.
Two types of deviation from Raoult's law: positive and negative. In positive deviation, the adhesion forces between the constituents are weaker than the cohesion forces, which results in a boiling point lower than expected. In negative deviation, the adhesion forces are stronger than the cohesion forces, causing a boiling point higher than expected.
Colligative properties: depend on the number of solute particles present in a solution and not on the nature of the constituents. Among these properties are the vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.
Vapor pressure lowering: As solute molecules are added to a solution, the vapor pressure of the solvent decreases, which results in a lowering of the vapor pressure of the solution.
Boiling point elevation: When a solute is added to a solvent, the boiling point of the solution increases.
Osmosis: A semi-permeable membrane separates a solution from a solvent. The solvent passes through the membrane into the solution, diluting it. The osmotic pressure is the pressure required to stop this process. For non-electrolytes, the osmotic pressure can be calculated using the formula pV = nRT, where n is the number of moles of solute, V the volume of the solution, and R the gas constant. For real solutions, the activity rather than the concentration should be used. Real solutions have a lower osmotic pressure than their concentration would lead us to expect.