5. Ideal and non-ideal solutions

Ideal and Non-ideal Solution

Ideal Solutions : Those solutions which obey Raoult's law over the entire range of conc. are called ideal solutions. When the forces of attraction between A—A, B—B is similar to A—B, then A and B will form ideal solution.

  Properties of ideal solution :

(i) Raoult's law is obeyed         

(ii) DH_mix = 0, i.e., there should not be enthalpy change when components of ideal solutions are mixed.

(iii) DV_mix = 0, (1L + 1L = 2L) i.e., there should not be change in volume on mixing. e.g.; n-hexane and n-heptane; ethyl bromide and ethyl iodide; benzene and toluene; chlorobenzene and bromobenzene form ideal solutions.

(iii) DS_mix = +ve  

(iv) DG_mix = –ve

Non^_Ideal Solutions :

Those solutions which do not obey Raoult's over the entire range of concentration are called non-ideal solutions.

When the forces of attraction between A—A, B—B is different from A—B then 'A' and 'B' form non-ideal solutions. For these solutions :

(i) Raoult's law is not obeyed. 

(ii) DH_mix ¹ 0 ;  

(iii) DV_mix ¹ 0.

Types of Non-Ideal Solutions : Non-ideal solution can be two types.

•  Non ideal solutions showing positive deviation
• Non ideal solutions showing negative deviation