Question

The mixture that forms maximum boiling azeotrope is:
(A) Water + Nitric acid
(B) Ethanol + Water
(C) Acetone + Carbon disulphide
(D) Heptane + Octane

Answer 1

Hint: To answer this question, we should know about azeotrope. We should know that azeotrope is a constant boiling point mixture. It is a mixture of two or more liquids.

Step by step answer:
So, first we will discuss azeotrope. If we know about azeotrope mixture then we can easily tell the mixture which leads to its formation. We should know that azeotrope is a mixture that contains liquid of the same concentration in the vapour phase and the liquid phase. If the concentration of mixture is same in vapour phase or liquid phase, then it is very hard to separate. We should know that azeotropes are of two types. First azeotrope mixture has higher boiling point than either of the components or they can have a lower boiling point. And after this we can say that azeotropes occur when a fraction of the liquids cannot be separated by distillation. We handle mixtures and try to separate them by distillation. But it is not possible in azeotropes.
To answer the above question we will use Raoult;s law. This law states that interactions between molecules of solute and molecules of solvent are the same as those molecules each are by themselves. And we can now say that azeotropes fail to prove the idea of Raoult;s law. We can say that during boiling, the component ratio of un-vaporized solution is equal to that of the vaporized solution. So, an azeotrope can be defined as a solution whose vapour has the same composition as its liquid.
Now, coming back to our question, the mixture that forms maximum boiling azeotrope is water and nitric acid. This mixture of water and nitric acid shows negative deviation from Roult's law and it will form maximum boiling azeotrope.

So, the correct option is A.

Note: We should know that it is extremely difficult for us to do the distillation of these types of substances. A very interesting fact that we should know is that the most concentrated form of ethanol, an azeotrope, is around 95.6% ethanol by weight because pure ethanol is basically non-existent.