NEET Chemistry Notes Solutions – Ideal Solutions

NEET Chemistry Notes Solutions – Ideal Solutions

 Ideal Solutions

Ideal Solutions

The solutions, which obey Raoult’s law are called ideal solutions.
For ideal solutions,
Solute-solute and solvent-solvent interactions  solute-solvent interactions.

Non-Ideal Solutions

The solution which shows deviation from Raoult’s law is called non-ideal solution.
For such solutions,

Practically no solution is ideals 3 The graphical representation of ideal solutions is given below.

Types of Non-ideal Solutions

•  Non-ideal Solutions Showing Positive Deviation When the observed vapour pressure is more than that expected by Raoult’s law, positive deviation is observed.
  For such a deviation
  
  
  Due to the formation of weaker bonds.
  
  For such solutions, i.e. .energy is absorbed on mixing and . These are usually obtained by mixing of polar liquids with non-polar ones.
  e.g. cyclohexane and ethanol, H₂O and C2H5OH.
  Minimum boiling azeotropes In case of positive deviation we get minimum boiling azeotropes, e.g
  C₂H₅OH (95.57%) + H₂O (4.43%)  (by mass).

 

•  Non-ideal Solutions Showing Negative Deviation

When the observed vapour pressure is less than that expected by Raoult’s law, this deviation is observed. For such solutions, i.e. energy is released on mixing and  i.e. attractive forces between unlike molecules are greater than the forces of attraction between like molecules.
e.g. chloroform and acetone.
For a solution showing negative deviation,

Maximum boiling azeotropes In case of negative deviation we get maximum boiling azeotropes, e.g. H₂O (20.22% by mass)+HCl.

Colligative Properties

• The properties which depend only on the number of moles of non-volatile solute are referred as colligative properties.
•  For different solutions of same molar concentration of different non-electrolyte solutes, the colligative properties have the same value for all.
•  For different molar concentrations of the same solute,
  the colligative property has greater value for more concentrated solution. ‘
•  For solutions of different solutes having same % strength, the colligative property has greater value for the solute having least molecular weight.
  There are four types of colligative properties as given below:

Relative Lowering of Vapour Pressure

Addition of non-volatile solute leads to the lowering of vapour pressure.

where, w_B and w_A = mass of solute and solvent respectively
M_B and M_A = molecular weight of solute and solvent respectively.

Elevation in Boiling Point

For dilute solutions,

• Depression in Freezing Point

For dilute solutions

Osmosis

Spontaneous flow of solvent molecules through a semipermeable membrane from a pure solvent to the solution (or from a dilute solution to concentrated solution) is termed as osmosis
Osmotic Pressure
n = moles of solute
C = molar concentration
V = volume of solution (in litre)
R = gas constant
T = temperature in kelvin(k)

If two solutions having same osmotic pressures at same temperature are termed as isotonic solutions.
When two solutions are being compared, the solution with higher osmotic pressure is termed as hypertonic and the solution with lower osmotic pressure is termed as hypotonic.
Osmotic pressure can be determined quite accurately, hence it is used in the determination of molecular weights of large proteins and similar substances.

van’t Hoff Factor (i)

In 1880 van’t Hoff introduced a factor i, known as the van’t Hoff factor, to account for the extent of dissociation or association. This factor i is defined as:

where, n = number of particles after dissociation.
Degree of association
Here, n = number of particles after association

Modified Expressions of Colligative Properties

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