Solutions Test - 6

Molarity is defined as several solutes dissolved in one litre of solution.

Molality is defined as the number of gas per kilogram of the solvent.

When a solute present in trace quantities. It is convenient to express concentration in terms of parts per million.

Example a litre of seawater (which weigh 1030g) contains about 6× 10-3g of dissolved oxygen (O₂). Such a small concentration is also expressed as 5.8 g per 10⁶g(5.8ppm) of seawater.

The concentration of pollutants in water or atmosphere is expressed in terms of µgmL^-1 or ppm.

The solution which obeys the Raoult’s law over the entire range of concentration is known as Ideal solution.

For an Ideal solution, the enthalpy of mixing of the pure component to form the solution is zero, and the volume of mixing is also zero,

∆_MIX H=0 and ∆_MIXV =0

It means that no heat is absorbed or evolved when the components are mixed.

The volume of the solution would be equal to the sum of volumes of the two components.

In an ideal solution.

At the molecular level, the ideal behaviour of the solution can be explained by considering two components.

The intermolecular attractive interactions will be types A-A and B-B, whereas in the binary solutions in addition to these two interactions, A-B type of interactions will also be present. If the intermolecular attractive forces between the A-A and B-B are nearly equal to those between A-B, this leads to the formation of an ideal solution.

Azeotropes are binary mixtures having the same composition in the liquid and vapour phase and boil at a constant temperature.

There are two types of azeotropes are

1) Minimum boiling azeotrope (Positive deviation from Raoult’s law)

2) Maximum boiling azeotrope (Negative deviation from Raoult’s law)