## Saturday, February 2, 2008

### IIt JEE Revision - Solutions - Introduction

a solution is a homogeneous mixture of two or more substances whose composition can be varied within certain limits.

In a solution, the component which is in excess is called solvent.

The component, that has lesser quantity is called solute.

In a solution particles are of molecular size (about 1000 pm) and the different components cannot be separated by any of the physical methods such as filtration, settling etc.

The concentration of a solution may be defined as the amount of solute present in the given quantity of the solution.

volume percent
Vol% = 100*volume of solute/(volume of solute + volume of solvent)

mass percent
mass % = 100*(mass of solute)/(mass of solute + mass of solvent)

parts per million
ppm = 10^6*(mass of solute)/(mass of solute + mass of solvent)

molality
m = number of moles of solute/kilograms of solvent

molar concentration or moles per liter or Molarity
M = number of moles of solute/liters solution

Mole fraction
Xy (y is subscript) = number of moles of y in mixture/totals moles in mixture

Normality
It is the number of gram equivalents of the solute dissolved per litre of the solution. It is denoted by N.

Normality (N) =

[Number of gram equivalents of solute]/[Volume of solution in litres]
Units of normality are gm equivalent per litre.

Formality
It is the number of formula masses of the solute dissolved per litre of the solution. It is represented by F.

Formality = [Number of formula masses of solute]/[Volume of the solution in litre]

Formality is used to express the concentrations of ionic substances like NaCl, CuSO4 etc. in solutions. They do not exist in solutions as discrete molecules. In these solutions, the sum of the atomic masses of various atoms constituting the formula of the compound (ionic) is called gram formula mass instead of molar mass.

Solubility of Gases in Liquids

Gases dissolve in liquids to form homogeneous solutions. The solubility of different gases in the same solvent varies. Gases which react with the solvent will be most soluble. The solubility of a gas decreases with temperature and increases with with increase of pressure over the solution at a given temperature.

Henry's Law
The mass of a gas dissolved per unit volume of the solvent at a given temperature is proportional to the pressure of the gas in equilibrium with the solution.

m is proportional to p
where m = mass of the gas dissolved in a unit volume of the solvent
p = pressure of the gas in equilibrium.

If pressure is more, more mass of gas is dissolved