Free Solutions and Colloids MCQs with Answers

11. Elevation of the boiling point is a _ property:

• A. Colligative
• B. None of these
• C. Constitutive
• D. Additive

Explanation: Boiling point elevation is a colligative property which means it depends on the presence and the number of dissolved particles and not on the solute's identity.

12. For a chemical reaction to occur, particles that collide should:

• A. All of these
• B. Have proper orientations
• C. Have proper energies
• D. Be in a homogenous mixture

Explanation: The collision theory states that for particles to take part in a chemical reaction, they must collide with one another, have sufficient energies, proper orientation, and should be in a homogenous mixture.

13. 10.0 grams of glucose are dissolved in water to make 100 cm3 of its solution, its molarity is:

• A. 0.55
• B. 0.1
• C. 10
• D. 1

Explanation: 0.55: This option suggests a molarity of 0.55 for the glucose solution. To determine the molarity, we need to calculate the number of moles of glucose present in the solution. Given that the mass of glucose is 10.0 grams and its molar mass is approximately 180.16 g/mol, we can calculate the number of moles using the formula:Number of moles = Mass of substance / Molar massNumber of moles of glucose = 10.0 g / 180.16 g/mol ≈ 0.0554 molNow, we can calculate the molarity using the formula:Molarity = Number of moles / Volume of solution (in liters)Since the volume of the solution is given as 100 cm3, we need to convert it to liters:Volume of solution = 100 cm3 / 1000 = 0.1 LMolarity = 0.0554 mol / 0.1 L ≈ 0.554 M

14. Which one of the following is the correct presentation for Ksp?

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: The solubility product constant, Ksp , is the equilibrium constant for a solid substance dissolving in an aqueous solution. It represents the level at which a solute dissolves in solution. The more soluble a substance is, the higher the Ksp value it has.

15. As the number of solute particles increases, the freezing point of the solution:

• A. Remains the same
• B. Increases
• C. First increases, then decreases
• D. Decreases

Explanation: When a solute is dissolved in a solvent, the freezing point of the solution decreases compared to the pure solvent. This happens because the solute particles disrupt the crystal lattice structure of the solvent, making it more difficult for the solvent to freeze. The extent to which the freezing point is lowered depends on the concentration of the solute particles in the solution.According to the Colligative property, the change in freezing point of a solution is directly proportional to the molality of the solution, which is the number of moles of solute per kilogram of solvent. Thus, as the number of solute particles increases, the molality of the solution increases, and so does the degree of depression of the freezing point. As a result, the freezing point of the solution lowers.

16. Boiling point constants help us to determine:

• A. Molar masses
• B. Volumes
• C. Pressures
• D. Masses

Explanation: Boiling point elevation is a colligative property that depends on the number of solute particles in a solution. The boiling point constant, Kb, is a proportionality constant that relates the molality of a solution to the elevation in boiling point.The equation for boiling point elevation is:ΔTb = Kb x molalitywhere ΔTb is the change in boiling point, Kb is the boiling point constant, and molality is the concentration of the solute in mol/kg of the solvent.By measuring the change in boiling point and knowing the boiling point constant of the solvent, we can calculate the molality of the solution. Then, using the molality and mass of the solute, we can calculate the molar mass of the solute. Therefore, boiling point constants help us to determine molar masses of solutes in solutions.

17. Mole fraction of any compound is the ratio of moles of all components in a:

• A. Compound
• B. Solution
• C. Molecule
• D. Solid

Explanation: Mole fraction is the ratio of moles of a particular component to the total number of moles of a solution.

18. Molarity is defined as the number of moles of any substance dissolved:

• A. Per dm3 of water
• B. In one gram of water
• C. Per m3 of water
• D. In 100 ml of water

Explanation: Molarity is the number of moles of any substance dissolved in 1 dm3 of water.

19. If 18.0 g of glucose is dissolved in 1 kg of water, boiling point of this solution should be:

• A. 100.52 °C
• B. 100.00 °C
• C. 100.052 °C
• D. Less than 100 °C

Explanation: Mass of glucose = 18 g Mass of solvent = 1 kg Boiling point of pure water = 100°C n (glucose) = 18 / [6(12) + 12(1) + 6(18)] = 18 /180 = 0.1 moles Molality (glucose) = n / mass of solvent = 0.1 / 1 = 0.1 molal ∆Tb = kb × molality = 0.52 × 0.1 = 0.052 Kelvin New boiling point = Boiling point of pure water + ∆Tb New boiling point = 100 + 0.052 = 100.052°C

20. Molal freezing point constant of water is:

• A. 1.86
• B. 2.86
• C. 11.86
• D. 0.52

Explanation: The molal freezing point depression constant for H2O, Kf , is given as 1.86 °C kg/mole. Thus a 1.00 m aqueous solution freezes at -1.86 °C instead of 0.00 °C which is the normal freezing point for water.