301. Which set of observations is most consistent with negative deviation from Raoult’s law?
ⓐ. Stronger unlike interactions, heat evolved on mixing, and volume contraction
ⓑ. Weaker unlike interactions, heat absorbed on mixing, and volume expansion
ⓒ. Equal unlike and like interactions, no heat change, and no volume change
ⓓ. Zero intermolecular interaction, zero vapour pressure, and no mixing
Correct Answer: Stronger unlike interactions, heat evolved on mixing, and volume contraction
Explanation: Negative deviation arises when unlike molecules attract each other more strongly than like molecules do. This lowers the escaping tendency of molecules, often releases heat on mixing, and may produce contraction in volume.
302. Compared with an ideal solution at the same composition, a solution showing positive deviation generally has
ⓐ. higher boiling point and lower vapour pressure
ⓑ. lower boiling point and higher vapour pressure
ⓒ. unchanged boiling point and unchanged vapour pressure
ⓓ. lower boiling point and zero vapour pressure
Correct Answer: lower boiling point and higher vapour pressure
Explanation: Positive deviation means the observed vapour pressure is greater than the ideal value. Since boiling occurs when vapour pressure becomes equal to external pressure, a liquid with higher vapour pressure reaches boiling at a lower temperature.
303. Which pair is a standard example of a solution showing negative deviation from Raoult’s law?
ⓐ. benzene and toluene
ⓑ. ethanol-acetone liquid mixture
ⓒ. nitric acid and water
ⓓ. hexane and heptane
Correct Answer: nitric acid and water
Explanation: Nitric acid and water show stronger attraction between unlike molecules than between like molecules. Because of this stronger interaction, the solution shows lower vapour pressure than the ideal prediction, giving negative deviation.
304. If unlike intermolecular attraction in a binary liquid solution is weaker than the attraction present in the pure liquids, then the total vapour pressure of the solution at a given composition will be
ⓐ. equal to the ideal value
ⓑ. lower than the ideal value
ⓒ. higher than ideal value
ⓓ. zero vapour pressure
Correct Answer: higher than ideal value
Explanation: Weaker unlike attraction allows molecules to escape more easily from the liquid mixture. Therefore, the observed vapour pressure becomes greater than the value predicted by Raoult’s law, giving positive deviation.
305. An azeotrope is best defined as a liquid mixture that
ⓐ. has only one volatile component
ⓑ. boils over a range of temperatures with changing composition
ⓒ. always behaves ideally at all compositions
ⓓ. boils without change in liquid-vapour composition
Correct Answer: boils without change in liquid-vapour composition
Explanation: At the azeotropic composition, the vapour formed has the same composition as the liquid. Therefore, the mixture boils like a pure substance without any change in composition during boiling.
306. A minimum boiling azeotrope is generally formed by a solution showing
ⓐ. negative deviation from Raoult’s law
ⓑ. positive deviation from Raoult’s law
ⓒ. ideal behaviour throughout the composition range
ⓓ. zero vapour pressure of both components
Correct Answer: positive deviation from Raoult’s law
Explanation: Positive deviation gives a vapour pressure higher than ideal, so the mixture boils at a lower temperature than expected. This can produce a minimum boiling azeotrope.
307. A maximum boiling azeotrope is generally associated with
ⓐ. weaker unlike interactions and positive deviation
ⓑ. equal unlike and like interactions and ideal behaviour
ⓒ. stronger unlike interactions and negative deviation
ⓓ. zero intermolecular attraction and complete volatility
Correct Answer: stronger unlike interactions and negative deviation
Explanation: Stronger unlike interactions lower the vapour pressure below the ideal value. As a result, the mixture may boil at a temperature higher than either pure component, giving a maximum boiling azeotrope.
308. At the azeotropic composition of a binary liquid mixture, which statement is correct?
ⓐ. The liquid is richer in the more volatile component than the vapour.
ⓑ. The vapour is richer in the less volatile component than the liquid.
ⓒ. The liquid and vapour have the same composition.
ⓓ. The total vapour pressure becomes zero.
Correct Answer: The liquid and vapour have the same composition.
Explanation: The defining feature of an azeotrope is equality of liquid and vapour compositions at the boiling point. Because of this, simple distillation cannot change the composition of the mixture at that point.
309. Which statement best explains why an azeotrope cannot be separated into its pure components by simple distillation?
ⓐ. The vapour and liquid have the same composition.
ⓑ. Both components become non-volatile at the azeotropic point.
ⓒ. The solution stops boiling at the azeotropic point.
ⓓ. The intermolecular forces become zero at the azeotropic point.
Correct Answer: The vapour and liquid have the same composition.
Explanation: Simple distillation works because vapour is usually richer in one component than the liquid. At the azeotropic composition, vapour and liquid compositions become identical, so distillation no longer changes the composition.
310. A minimum boiling azeotrope is generally associated with
ⓐ. negative deviation and stronger unlike interactions
ⓑ. positive deviation and higher total vapour pressure
ⓒ. ideal behaviour and zero enthalpy of mixing
ⓓ. non-volatile solute and zero vapour pressure
Correct Answer: positive deviation and higher total vapour pressure
Explanation: Positive deviation makes the observed vapour pressure greater than the ideal value. A higher vapour pressure means the mixture reaches the boiling condition at a lower temperature, so a minimum boiling azeotrope may form.
311. Which statement is correct for a maximum boiling azeotrope?
ⓐ. It is formed only by ideal solutions.
ⓑ. It boils at a temperature lower than either pure component.
ⓒ. It boils above either pure component.
ⓓ. It always contains one non-volatile solute.
Correct Answer: It boils above either pure component.
Explanation: A maximum boiling azeotrope arises from negative deviation from Raoult’s law. Because the vapour pressure is lower than expected, a higher temperature is needed for boiling, so the boiling point becomes greater than that of either pure component.
312. During simple distillation of a liquid mixture, the distillate composition gradually changes and finally becomes constant at a particular composition. This constant-composition mixture is
ⓐ. an ideal solution
ⓑ. a saturated solution
ⓒ. a supersaturated solution
ⓓ. an azeotrope
Correct Answer: an azeotrope
Explanation: An azeotrope is a constant-boiling mixture whose vapour has the same composition as the liquid. Once this composition is reached, simple distillation cannot alter it further.
313. A mixture of ethanol and water is a standard example of
ⓐ. a maximum boiling azeotrope with negative deviation
ⓑ. a minimum boiling azeotrope with positive deviation
ⓒ. an ideal solution over the full composition range
ⓓ. a non-volatile solute solution
Correct Answer: a minimum boiling azeotrope with positive deviation
Explanation: Ethanol-water is a common example of a mixture that shows positive deviation from Raoult’s law. Because of the higher vapour pressure than ideal, it forms a minimum boiling azeotrope.
314. A mixture of nitric acid and water is commonly cited as an example of
ⓐ. a minimum boiling azeotrope with positive deviation
ⓑ. an ideal solution with \( \Delta H_{\text{mix}}=0 \)
ⓒ. a maximum boiling azeotrope with negative deviation
ⓓ. a binary solution of two non-volatile liquids
Correct Answer: a maximum boiling azeotrope with negative deviation
Explanation: Nitric acid-water shows strong unlike interactions and negative deviation from Raoult’s law. Such behaviour is associated with formation of a maximum boiling azeotrope.
315. Which statement is correct for a minimum boiling azeotrope?
ⓐ. It has lower vapour pressure than either pure component.
ⓑ. It is formed only when \( \Delta V_{\text{mix}}=0 \).
ⓒ. It must always obey Raoult’s law exactly.
ⓓ. It has higher vapour pressure and lower boiling point.
Correct Answer: It has higher vapour pressure and lower boiling point.
Explanation: A minimum boiling azeotrope results from positive deviation. The solution then has relatively high vapour pressure, so it boils at a temperature lower than either pure liquid.
316. Which statement correctly links deviation and azeotrope type?
ⓐ. Negative deviation usually gives a maximum boiling azeotrope.
ⓑ. Negative deviation usually gives a minimum boiling azeotrope.
ⓒ. Positive deviation usually gives a maximum boiling azeotrope.
ⓓ. Ideal behaviour always gives a maximum boiling azeotrope.
Correct Answer: Negative deviation usually gives a maximum boiling azeotrope.
Explanation: Negative deviation means stronger unlike interactions and lower vapour pressure than ideal. Because a higher temperature is then required for boiling, the mixture may form a maximum boiling azeotrope.
317. Which statement correctly compares a minimum boiling azeotrope with a maximum boiling azeotrope?
ⓐ. Both boil at temperatures lower than either pure component.
ⓑ. Both boil at temperatures higher than either pure component.
ⓒ. A minimum boiling azeotrope boils lower, while a maximum boiling azeotrope boils higher than the pure components.
ⓓ. A minimum boiling azeotrope has lower vapour pressure, while a maximum boiling azeotrope has higher vapour pressure.
Correct Answer: A minimum boiling azeotrope boils lower, while a maximum boiling azeotrope boils higher than the pure components.
Explanation: A minimum boiling azeotrope is associated with positive deviation and relatively high vapour pressure, so it boils at a lower temperature. A maximum boiling azeotrope is associated with negative deviation and relatively low vapour pressure, so it boils at a higher temperature.
318. Which statement is correct for a binary azeotropic mixture at its boiling point?
ⓐ. The composition of vapour is the same as that of the liquid.
ⓑ. The vapour always contains only the more volatile component.
ⓒ. The liquid always contains only the less volatile component.
ⓓ. The total vapour pressure becomes independent of temperature.
Correct Answer: The composition of vapour is the same as that of the liquid.
Explanation: The defining property of an azeotrope is equality of liquid and vapour compositions at the boiling point. Because of this, distillation does not enrich one component over the other at that composition.
319. Which statement about separation of azeotropic mixtures by ordinary fractional distillation is correct?
ⓐ. They can always be separated completely into pure components.
ⓑ. They separate more easily than ideal solutions.
ⓒ. They can be separated only when both components have equal molar masses.
ⓓ. Complete separation is not possible by ordinary fractional distillation.
Correct Answer: Complete separation is not possible by ordinary fractional distillation.
Explanation: Fractional distillation depends on repeated enrichment of vapour in one component. At the azeotropic composition, vapour and liquid compositions are identical, so further separation by ordinary distillation is not possible.
320. Which statement correctly links intermolecular interaction and azeotrope type?
ⓐ. Stronger unlike interaction usually leads to a minimum boiling azeotrope.
ⓑ. Stronger unlike interaction usually leads to a maximum boiling azeotrope.
ⓒ. Weaker unlike interaction always gives ideal behaviour.
ⓓ. Equal unlike and like interactions always give a maximum boiling azeotrope.
Correct Answer: Stronger unlike interaction usually leads to a maximum boiling azeotrope.
Explanation: Stronger attraction between unlike molecules causes negative deviation from Raoult’s law. This lowers vapour pressure and raises the boiling point, which can produce a maximum boiling azeotrope.
