Question

The boiling point of 95% ethanol is higher than that of absolute ethanol
a.) True
b.) False

Answer 1

Hint: In the mixture of water and ethanol an intermolecular bond exists between some ethanol and water molecules. When liquid easily turns into vapour the attraction between molecules is not strong enough as it vaporized easily that is its vapour pressure is high and its boiling point is low. If the molecules in liquid have strong intermolecular force of attraction between them then the boiling point will be high as it requires more heat to break the bond between them and vaporize, so vapour pressure will be low.

Complete step by step answer:
Boiling point can be defined as the temperature at which the vapour pressure of liquid is equal to the atmospheric pressure surrounding it.
 Now to understand the concept behind this question we should know Raoult's law which states that ''The partial pressure of any volatile component of a solution at any temperature is equal to the vapour pressure of pure component multiplied by the mole fraction of the component''.

The binary solution that obeys Raoult's law under all concentration and all temperature is said to be the ideal solution. The binary solution that shows either positive or negative deviation from Raoult's law is said to be a non-ideal solution. The binary solution of ethanol in water shows large positive deviation from Raoult's law. When it positively deviates from Roault's law there will be a maximum point. At this particular point concentration at which the mole fraction of both the components will be fixed is in liquid state as well as in vapour state. When the concentration of components in the liquid state and in the vapour state will become equal and when they become equal the entire mixture starts boiling at a particular boiling point, this is called constant boiling mixture or azeotropic mixture.

Ethanol forms an azeotropic mixture with water, when it contains 95% ethanol and 5% water. The vapour pressure is inversely related to boiling point of a substance. In this case there is a large positive deviation so the vapour pressure will be high so the boiling point will be. The azeotropic mixture has minimum boiling point.

95% ethanol forms azeotropic mixture that is beyond this concentration yielding ethanol is very difficult as no matter how many times the 95% ethanol is boiled and condensed will arrive at the same concentration. Absolute ethanol contains 99% ethanol and 1% water. Stream distillation of 95% ethanol is impossible but absolute ethanol can be yielded by azeotropic distillation. From the above discussion we can come to a conclusion that to yield absolute ethanol more energy is needed that is heat than that of 95% ethanol, so absolute ethanol will have more boiling point than 95% ethanol.
   So, the correct answer is “Option B”.

Note: As the vapour pressure increases the boiling point decreases and vice-versa. In an azeotropic mixture that is 95% ethanol no matter how many times this binary solution is boiled and condensed will arrive at the same concentration.