Question

Which one of the following is not a non-ideal solution showing positive deviation?
(A) Benzene & Acetone
(B) $CC{l_4}\;\& \;CHC{l_3}$
(C) Acetone & Ethyl alcohol
(D) Benzene & Toluene

Answer 1

Hint: As per the question, we need to check either the solution is ideal or the solution is non-ideal showing negative deviation. Ideal solutions are the kind of solution which obey Raoult's law at all temperatures and at every range of concentration while the negative deviation in case of non-ideal solutions is observed when the total vapour pressure is less than expected.

Complete Step by Step Solution:
Raoult’s law: A relationship was proposed by a French chemist, Francois Marte Raoult, according to which the mole fraction of the solute varies directly with its partial pressure.
According to Raoult's law, the solutions are categorised into two types, Ideal and non-ideal solution.

Ideal Solution: These are the types of solutions which obey Raoult's law at all sets of concentrations and temperatures. This can usually be achieved when solute and solvent having similar molecular structure and size are mixed at certain conditions.
The intermolecular force of attraction between the molecules of solute and solvent must be nearly equal for obtaining an ideal solution. The examples of ideal solutions are Benzene and toluene, n-hexane and n-heptane, bromoethane and chloroethane, etc.

Non-ideal solutions: The solutions which do not obey Raoult's law at certain temperature and concentration are known as non-ideal solutions. These types of solutions are divided into two categories based on the value of total vapour pressure, the solution with positive deviation and negative deviation.

Positive deviation from Raoult’s Law is observed when the vapour pressure of the solution is greater than expected as in case of Raoult’s law whereas the negative deviation is observed when the total vapour pressure is less than expected as per Raoult’s law. The examples of positive deviation are Benzene and acetone, $CC{l_4}\;\& \;CHC{l_3}$, Acetone & ethyl alcohol, ethanol and water, etc and the examples of negative deviation are chloroform and benzene, acetone and aniline, etc. Hence, as per the given options, the solution which does not show positive deviation is benzene and toluene.

Thus, option (D) is the correct answer.

Note: It is important to note that the solution of benzene and toluene is ideal solution which depicts that on mixing benzene with toluene, no heat is released or absorbed while mixing and the volume of mixing benzene and toluene is also zero i.e., $\Delta {H_{mix}} = 0\;\;\& \;\;\Delta {V_{mix}} = 0$.