Comparison Between Ideal and Non-ideal Solutions    

Ideal solutions

Non-ideal solutions

Positive deviation from Raoult’s law

Negative deviation from Raoult’s law

1.Obey Raoult’s law at every range of concentration.   2.?Hmix = 0; neither is evolved nor absorbed during dissolution.   3.?Vmix = 0; total volume of solution is equal to sum of volumes of the components.   4.P = pA + pB = pA0XA + pB0XB

   i.e., pA =     5.A—A, A—B, B—B interactions should be same, i.e., ‘A’ and ‘B’ are identical in shape, size and character.       6. Escaping tendency of ‘A’ and ‘B’ should be same in pure liquids and in the solution.  

Examples: dilute solutions; benzene + toluence: n-hexane + n-heptane; chlorobenzene + bromobenzene; n-butyl chloride + n-butyl bromide.

1.Do not obey Raoult’s law.     2.?Hmix>0. Endothermic dissolution; heat is absorbed.   3.?Vmix > 0. Volume is increased after dissolution.

4.pA > pA0XA; pB > pB0XB

∴ pA + pB > pA0XA + pB0XB   5.A—B attractive force should be weaker than A—A and B—B attractive forces. ‘A’ and ‘B’ have different shape, size and character.       6. ‘A’ and B’ escape easily showing higher vapour pressure than the expected value.     Examples: acetone + ethanol acetone + CS2; water + methanol; water + ethanol; CCl4 + toluene; CCl4 + CHCl3; acetone + benzene; CCl4 + CH3OH; Cyclohexane + ethanol

1.Do not obey Raoult’s law.     2.?Hmix<0. Exothermic dissolution; heat is evolved.   3.?Vmix <0. Volume is decreased during dissolution.     4.pA < pA0XA; pB < pB0XB

∴ pA + pB < pA0XA + pB0XB     5. A—B attractive force should be greater than A—A and B—B attractive forces. ‘A’ and ‘B’ have different shape, size and character.   6. Escaping tendency of both components ‘A’ and ‘B’ is lowered showing lower vapour pressure than expected ideally.   Examples: acetone + aniline; acetone + chloroform; CH3OH + CH3COOH; H2O + HNO3; Choloroform + diethyl ether, water + HCl; acetic acid + pyridine; chloroform + benzene.

 

1783_Graphical Representation of Ideal and Non-ideal Solutions.JPG

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