Chemistry

Solutions and Vapour Pressure

62 Questions

Solutions and vapour pressure questions explore boiling points, colligative properties, and osmotic pressure. These concepts are regularly tested in competitive chemistry exams. Solving these requires a solid grasp of solute and solvent interactions.

colligative propertiesvapour pressureboiling and melting pointsosmotic pressure

Solutions and Vapour Pressure Questions

Multiple choice

At 273 K, 10 g glucose (p1), 10 g urea (p2) and 10 g sucrose (p3) are dissolved in 250 mL of water. The order of osmotic pressures (p1, p2 and p3), of above solutions is

  1. P1 > p2 > p3

  2. P1 > p3 > p2

  3. P2 > p1 > p3

  4. P3 > p1 > p2

  5. P3 > p2 > p1
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since, equal weight of all electrolytes has been used. Higher the molecular weight, lower the number of moles and lower the magnitude of colligative properties like osmotic pressure. Molecular weight order is sucrose > glucose > urea. Hence, the order of osmotic pressures (p1, p2 and p3) of the above solutions is urea (p2) > glucose (p1) > sucrose (p3).

Multiple choice

Van Laar equation deals with the activity coefficients in _____________.

  1. heterogeneous azeotrope

  2. zeotropic mixture

  3. azeotropic mixture

  4. ternary solutions

  5. binary solutions
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The general characteristic of binary solution is that when, say, two liquids are mixed together at the same pressure and temperature, the extensive properties (volume, enthalpy, entropy, etc.) of the mixture are not the sum of those of the unmixed components.

Multiple choice

A solution of urea in water has a vapour pressure of 266.3 torr. The vapour pressure of pure water is 355.1 torr. Calculate the mole fraction of urea in the solution.

  1. 0.25

  2. 0.50

  3. 0.75

  4. 1.0

  5. 1.25
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Correct answer. Urea is non-volatile. Water obeys Raoult’s law. Pwater = Xwater x P°water 266.3 torr = Xwater x (355.1 torr) Xwater = 266.3 / 355.1 = 0.75 From equation, X1 + X2 + X3 ...... = 1 Xurea + Xwater = 1 Xurea = 1 – 0.75 = 0.25

Multiple choice

Calculate the vapour pressure of a 65 percent (W/W) solution of ordinary cane sugar (C22O11H22, MW = 342 g mol−1) in water. The vapour pressure of pure water at the same temperature is 26.0 torr.

  1. 16.9 torr

  2. 26.0 torr

  3. 23.7 torr

  4. 34.2 torr

  5. 52.0 torr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Correct answer. 100 g of solution contains 65/342 = 0.19 mol of sugar and 36/18 = 2 mol of water  The mole fraction of water in the solution = 2 / (0.19 + 2) = 0.91 So, its vapour pressure will be 0.91 × 26.0 torr = 23.7 torr

Multiple choice

The minimum boiling point of azeotrope is dependent upon which of the following points?

  1. Positive deviation from Raoult's law

  2. Negative deviation from Raoult's law

  3. Ideal solution

  4. Options (2) and (3)

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This option is correct because certain composition of this non-ideal solution shows positive deviation, the vapour pressure of the solution is the highest and its boiling point is lowest. Such non-ideal solutions show the minimum boiling point of azeotropes.

Multiple choice

Which of the following statements is/are incorrect?

1. Vapour pressure of liquid is the measure of the strength of intermolecular attractive force.

  1. Surface tension of liquid acts perpendicular to the surface of liquid.
  2. Vapour pressure of all the liquids is the same at their freezing point.

  1. All of the above

  2. Only 1 and 2

  3. Only 3

  4. Only 1 and 3

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This option is correct because the vapour pressure of all liquids is different at their freezing point.

Multiple choice

When a non volatile substance is dissolved in solvent, the vapour pressure of the solvent decreases. This results in ____________.

  1. an increase in boiling point of the solvent

  2. a decrease in the boiling point of solvent

  3. the solution will have a higher freezing point than the solvent

  4. the solution will have lower osmotic pressure than the solvent

  5. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This option is correct because the boiling point of liquid in the temperature at which its vapour pressure is equal to atmospheric pressure of liquid, is lowered. When a non volatile solute is added, the temperature of solution of vapour pressure will be equal to the atmospheric pressure and will be higher than the temperature of pure solvent. Boiling point of solution increases by addition of non-volatile substance.

Multiple choice

The molecular weight of a substance can be calculated by measuring

  1. density in liquid state

  2. freezing point

  3. vapour density

  4. vapour pressure
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Vapor density is the density of a vapor in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen.