Try each question on your own first. Use the Show Answer button only after you have selected your option, then read the explanation and revise the related concept from your chapter notes.
1. Molarity is defined as the number of moles of solute per:
A. Litre of solution
B. Kg of solvent
C. Litre of solvent
D. Kg of solution
Answer: A. Litre of solution
Explanation: Molarity (M) is defined as moles of solute dissolved per litre of solution.
2. Which colligative property is most suitable for determining the molar mass of macromolecules such as proteins and polymers?
A. Osmotic pressure
B. Relative lowering of vapour pressure
C. Elevation in boiling point
D. Depression in freezing point
Answer: A. Osmotic pressure
Explanation: Osmotic pressure produces a measurable value even for very dilute solutions of macromolecules, making it the most accurate method.
3. Raoult's law states that the partial vapour pressure of each component in a solution is proportional to:
A. Its mole fraction
B. Its molarity
C. Its molality
D. Its mass fraction
Answer: A. Its mole fraction
Explanation: According to Raoult's law, p_i = x_i * p_i°, where x_i is the mole fraction of component i.
4. Which of the following pairs shows positive deviation from Raoult's law?
A. Ethanol and acetone
B. HCl and water
C. Chloroform and acetone
D. Acetic acid and pyridine
Answer: A. Ethanol and acetone
Explanation: Ethanol-acetone mixtures have weaker A-B interactions than A-A/B-B interactions, causing positive deviation.
5. The van't Hoff factor (i) is greater than 1 for solutes that:
A. Dissociate into ions in solution
B. Associate in solution
C. Are non-electrolytes
D. Do not ionize at all
Answer: A. Dissociate into ions in solution
Explanation: Dissociation increases the number of particles in solution, making i > 1.
6. Molality of a solution is independent of:
A. Temperature
B. Amount of solute
C. Mass of solvent
D. Nature of solute
Answer: A. Temperature
Explanation: Since molality is defined using mass (not volume) of solvent, it does not change with temperature.
7. The SI unit of the ebullioscopic constant (Kb) is:
A. K kg mol⁻¹
B. mol kg⁻¹
C. K mol⁻¹
D. kg mol⁻¹ K⁻¹
Answer: A. K kg mol⁻¹
Explanation: Kb relates the elevation in boiling point (K) to molality (mol kg⁻¹), giving units K kg mol⁻¹.
8. Azeotropes are mixtures of two liquids that:
A. Have the same composition in liquid and vapour phase and boil at a constant temperature
B. Are pure compounds
C. Always behave as ideal solutions
D. Always obey Raoult's law
Answer: A. Have the same composition in liquid and vapour phase and boil at a constant temperature
Explanation: Azeotropic mixtures cannot be separated by simple distillation because the vapour has the same composition as the liquid.
9. Henry's law is primarily used to determine the:
A. Solubility of a gas in a liquid
B. Solubility of a solid in a liquid
C. Vapour pressure of a pure liquid
D. Boiling point elevation of a solution
Answer: A. Solubility of a gas in a liquid
Explanation: Henry's law states that the partial pressure of a gas is proportional to its mole fraction dissolved in a liquid.
10. For an ideal solution, the enthalpy of mixing (ΔH_mix) is:
A. Zero
B. Positive
C. Negative
D. Undefined
Answer: A. Zero
Explanation: Ideal solutions form with no net heat change because solute-solvent interactions equal solute-solute and solvent-solvent interactions.
11. Which of the following 0.1 m aqueous solutions has the highest boiling point?
A. Al2(SO4)3
B. NaCl
C. Glucose
D. Urea
Answer: A. Al2(SO4)3
Explanation: Al2(SO4)3 dissociates into the largest number of ions, giving the highest van't Hoff factor and hence the greatest boiling point elevation.
12. Reverse osmosis is commonly used for:
A. Desalination of sea water
B. Determining the molar mass of solutes
C. Preparing azeotropic mixtures
D. Increasing the vapour pressure of a solution
Answer: A. Desalination of sea water
Explanation: In reverse osmosis, pressure greater than osmotic pressure is applied to force pure water through a semi-permeable membrane, leaving salts behind.
