Solutions

Osmotic Pressure:

Osmotic pressure is the minimum pressure that must be applied to a solution to prevent the flow of solvent molecules into it through a semipermeable membrane.

It is a colligative property and is given by: where:

• = osmotic pressure
• = molar concentration of solute
• = universal gas constant
• = absolute temperature

Step 1: Recall the formula for freezing point depression.

where:

• = depression in freezing point
• = van’t Hoff factor (number of particles formed per formula unit)
• = cryoscopic constant (for water = 1.86 K·kg·mol )
• = molality

Step 2: Calculate .

The freezing point of pure water = . Given freezing point of solution = .

Step 3: Value of for KBr.

KBr dissociates completely in water as: So, .

Step 4: Substitute values in the formula.

Step 5: Solve for molality.

Final Answer:

The molality of the solution is

Henry's Law:

Henry's law states that: The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid at constant temperature.

Mathematically: where:

• = concentration (or solubility) of the gas in the liquid
• = partial pressure of the gas
• = Henry’s law constant