Solutions and Colligative Properties

## Concentration

It is the strength of the Solution

Molarity changes with change in temperature and pressure , because Volume changes with these parameters .

For dilution ; M1V1 = M2V2 NOTE : MV = no. of moles

For mixing ; MRVT= M1V1 + M2V2 + M3V3 .......+ MnVn

### **Demal Unit**

A demal unit is number of moles of solution one litre of solution at 0o C

### **Molality**

Molality = No. of Moles of Solute / Mass of Solution (kg) = n / m

Molality remains constant with change in temperature and pressure , because number of moles and mass does not change with these parameters .

### **Formality**

Formality is the number of gram formula weights per litre of solution .

### **Normality**

Normality is the number of equivalents present in one litre of solution .

Normality = [(Mass of Solute) / (Equivalent weight of Solute x Volume of Solution )]

N1V1= N2V2

### **Mole Fraction**

Mole Fraction = No. of Moles of Solute / No. of moles of Solution

Note that is a fraction and not a percentage .

## Solvation

The process of particles of a solvent surrounding the solute is called as Solvation . The process of ionization by a solvent is called as Solvolysis . If the solvent is water it is called as Hydrolysis . Solvolyis occurs only if the Solvent is polar . Water is a polar molecule ; that is why it can ionize NaCl .

## Solubility of Gases in Liquids

Effect of temperature : Inversely Proportional . Because as temperature increases , the volume of gas increases more than that of liquid due to which the liquid becomes inadequate for solvation .

Effect of Pressure : Directly Proportional . Volume Increases with decrease in Pressure .

Effect of addition of soluble salt : The soluble salt will displace the gas to get dissolved . The gas will be released from the liquid with formation of bubbles .

## Lowering of Vapour Pressure

**Vapour Pressure :** Vapour pressure is the amount of pressure exerted by the vapour of a liquid on the surface of the liquid , when it is in equilibrium .

**Vapour Pressure lowering :** Vapour Pressure can be lowered by adding non-volatile solute in a solution .

**Relative lowering of Vapour Pressure**

## Raoult's Law

for non-volatile solution : Po- P1 / Po = x2

Molar mass and relative lowering of vapour pressure

## Boiling Point Elevation

Boiling Point is the temperature at which the vapour pressure of the liquid becomes equal to the vapour pressure of the atmosphere .

Boiling Point can be increased by increasing the external pressure .

## Freezing Point Depression

Freezing point is the temperature at which the vapour pressure of liquid becomes equal to the vapour pressure of solid .

Freezing Point Depression is directly proportional to Vapour pressure lowering and molality .

## Osmosis

The semi-permeable membrane allows solvent particles to pass but not the solute particles . The spontaneous and unidirectional flow of solvent molecules through a semi-permeable membrane into the solution is called Osmosis . The solvent molecules move from a solution of lower concentration to higher concentration through the semi-permeable membrane .

## Osmotic Pressure

The excess of pressure on the side of solution that stops the net flow of solvent into solution through semipermeable membrane is called osmotic pressure .

 Two or more solutions having the same osmotic pressure are called as isotonic solutions . A solution having osmotic pressure higher than that of other solution , then i is called as hypertonic with that solution .

A solution having osmotic pressure lower than that of another solution is said to be hypotonic with that solution .

## Van't-Hoff - Boyle's Law

At constant temperature , the osmotic pressure (π) of a dilute solution is directly proportional to the Molar concentration and inversely proportional to the volume of the solution .

π α C / V

## Van't Hoff - Charle's Law

At constant concentration , the osmotic pressure of a dilute solution is directly proportional to the absolute temperature .

π α T

## Van't Hoff' General Solution Equation

π α T/V

π = CRT