Solutions: Multiple Choice Questions (MCQs)

Multiple Choice Questions (MCQs) and Explanations

Here are 40 MCQs based on the “Solutions” notes, with detailed explanations.

Question 1: A solution is a homogeneous mixture of two or more: (A) Reacting components (B) Non-reacting components (C) Only solid components (D) Only liquid components

Explanation 1:

Correct Answer: (B)
Reasoning: By definition, a solution is a homogeneous mixture of two or more non-reacting components. If components react, they form new substances, not a simple solution.

Question 2: Which of the following concentration terms is independent of temperature? (A) Molarity (B) Normality (C) Volume percentage (D) Molality

Explanation 2:

Correct Answer: (D)
Reasoning: Molarity, Normality, and Volume percentage are all defined in terms of volume of solution, which changes with temperature. Molality is defined in terms of mass of solvent, which is independent of temperature.

Question 3: What is the Henry’s Law constant (KH) if the partial pressure of a gas is 0.8 bar and its mole fraction in a solution is 0.02? (A) 0.016 bar (B) 40 bar (C) 0.025 bar (D) 16 bar

Explanation 3:

Correct Answer: (B)
Reasoning: According to Henry’s Law, p=KH×χ. KH=p/χ=0.8 bar/0.02=40 bar.

Question 4: When a non-volatile solute is added to a solvent, the freezing point of the solution: (A) Increases (B) Decreases (C) Remains unchanged (D) First increases then decreases

Explanation 4:

Correct Answer: (B)
Reasoning: This is a colligative property known as depression in freezing point. The presence of non-volatile solute particles hinders the solvent molecules from forming the solid crystal lattice, requiring a lower temperature to freeze.

Question 5: Which of the following statements is true for an ideal solution? (A) ΔHmix>0 (B) ΔVmix<0 (C) It obeys Raoult’s Law over the entire range of concentrations. (D) A-B interactions are stronger than A-A and B-B interactions.

Explanation 5:

Correct Answer: (C)
Reasoning: An ideal solution is defined as one that obeys Raoult’s Law at all concentrations and temperatures. For ideal solutions, ΔHmix=0 and ΔVmix=0, and intermolecular forces are similar.

Question 6: What is the unit of Molal Elevation Constant (Kb)? (A) K mol−1 (B) K kg mol−1 (C) K kg−1 (D) K mol kg−1

Explanation 6:

Correct Answer: (B)
Reasoning: ΔTb=Kb×m. Since ΔTb is in K and molality (m) is in mol kg−1, Kb must have units of K / (mol kg−1)=K kg mol−1.

Question 7: A solution shows negative deviation from Raoult’s Law. This indicates that: (A) A-B interactions are weaker than A-A and B-B interactions. (B) The vapor pressure of the solution is higher than expected. (C) ΔHmix<0 (exothermic). (D) ΔVmix>0 (volume increases).

Explanation 7:

Correct Answer: (C)
Reasoning: Negative deviation occurs when A-B interactions are stronger than A-A and B-B interactions. This leads to a lower observed vapor pressure, a release of heat (ΔHmix<0), and a decrease in volume (ΔVmix<0).

Question 8: The phenomenon of osmosis involves the flow of: (A) Solute from higher concentration to lower concentration. (B) Solvent from higher concentration to lower concentration. (C) Solute from lower concentration to higher concentration through SPM. (D) Solvent from lower solute concentration to higher solute concentration through SPM.

Explanation 8:

Correct Answer: (D)
Reasoning: Osmosis is the net movement of solvent molecules from a region of higher solvent concentration (or lower solute concentration) to a region of lower solvent concentration (or higher solute concentration) through a semi-permeable membrane.

Question 9: What will be the van’t Hoff factor (i) for a NaCl solution, assuming 100% dissociation? (A) 1 (B) 2 (C) 0.5 (D) 3

Explanation 9:

Correct Answer: (B)
Reasoning: NaCl dissociates into two ions: NaCl→Na++Cl−. Since one molecule yields two particles, if dissociation is 100%, i = 2.

Question 10: Which of the following solutions will have the highest boiling point? (Assume non-volatile solutes and equal molality) (A) Glucose (B) Urea (C) Sodium chloride (D) Sucrose

Explanation 10:

Correct Answer: (C)
Reasoning: Boiling point elevation is a colligative property. Among the given options, NaCl dissociates into 2 ions (Na+ and Cl−), so its van’t Hoff factor (i) is 2. Glucose, urea, and sucrose are non-electrolytes (i=1). Higher ‘i’ value means more particles, leading to a greater elevation in boiling point.

Question 11: What is the mass percentage (% w/w) of a solution prepared by dissolving 20 g of NaOH in 80 g of water? (A) 20% (B) 25% (C) 80% (D) 100%

Explanation 11:

Correct Answer: (A)
Reasoning: Mass of solute (NaOH) = 20 g. Mass of solvent (water) = 80 g. Mass of solution = Mass of solute + Mass of solvent = 20+80=100 g. Mass % = (Mass of solute/Mass of solution) ×100=(20/100)×100=20%.

Question 12: Which colligative property is most suitable for determining the molar mass of polymers? (A) Relative lowering of vapor pressure (B) Elevation in boiling point (C) Depression in freezing point (D) Osmotic pressure

Explanation 12:

Correct Answer: (D)
Reasoning: Osmotic pressure is measured at room temperature and is very sensitive to small changes in solute concentration. Other colligative properties give very small changes in values for high molar mass polymers, making them difficult to measure accurately.

Question 13: If the dissolution of a solid in a liquid is an endothermic process, how does its solubility change with increasing temperature? (A) Decreases (B) Increases (C) Remains constant (D) Cannot be determined

Explanation 13:

Correct Answer: (B)
Reasoning: According to Le Chatelier’s principle, for an endothermic process (ΔHsol>0), increasing the temperature shifts the equilibrium towards the dissolution side, thus increasing solubility.

Question 14: Which of the following conditions represents a saturated solution? (A) More solute can be dissolved at that temperature. (B) No more solute can be dissolved at that temperature. (C) Contains less solute than the maximum possible. (D) Contains more solute than the maximum possible.

Explanation 14:

Correct Answer: (B)
Reasoning: A saturated solution is one in which the maximum amount of solute has been dissolved at a given temperature, and no more solute can dissolve.

Question 15: Benzene and toluene form an ideal solution. This implies: (A) ΔHmix<0 (B) ΔVmix>0 (C) They obey Raoult’s Law. (D) They form an azeotrope.

Explanation 15:

Correct Answer: (C)
Reasoning: Ideal solutions are characterized by obeying Raoult’s Law, having zero enthalpy of mixing (ΔHmix=0), and zero volume change on mixing (ΔVmix=0).

Question 16: The process of converting seawater into fresh water by applying pressure greater than osmotic pressure is called: (A) Osmosis (B) Reverse osmosis (C) Diffusion (D) Dialysis

Explanation 16:

Correct Answer: (B)
Reasoning: Reverse osmosis is the process where a pressure greater than the osmotic pressure is applied to the solution side, forcing the solvent to flow from the solution to the pure solvent side through a semi-permeable membrane. This is used in desalination.

Question 17: The mole fraction of solute in a 2.5 m aqueous solution is approximately: (Molar mass of water=18 g/mol) (A) 0.043 (B) 0.025 (C) 0.05 (D) 0.018

Explanation 17:

Correct Answer: (A)
Reasoning: Molality (m) = Moles of solute / Mass of solvent (kg). For 2.5 m aqueous solution, it means 2.5 moles of solute in 1 kg (1000 g) of water. Moles of water = 1000 g/18 g/mol≈55.55 moles. Mole fraction of solute (χsolute) = Moles of solute / (Moles of solute + Moles of water) χsolute=2.5/(2.5+55.55)=2.5/58.05≈0.043.

Question 18: Which of the following factors does not affect the solubility of a solid in a liquid? (A) Temperature (B) Nature of solute (C) Nature of solvent (D) Pressure

Explanation 18:

Correct Answer: (D)
Reasoning: Pressure has a negligible effect on the solubility of solids in liquids. It primarily affects the solubility of gases in liquids.

Question 19: If a NaCl solution has a higher osmotic pressure than a cell, the solution is: (A) Isotonic (B) Hypotonic (C) Hypertonic (D) Saturated

Explanation 19:

Correct Answer: (C)
Reasoning: A solution with a higher osmotic pressure than another solution is termed hypertonic. If cells are placed in a hypertonic solution, water will move out of the cells, causing them to shrink (crenation).

Question 20: The statement “The partial pressure of the gas in vapor phase is proportional to the mole fraction of the gas in the solution” is known as: (A) Raoult’s Law (B) Dalton’s Law (C) Henry’s Law (D) Avogadro’s Law

Explanation 20:

Correct Answer: (C)
Reasoning: This is the precise statement of Henry’s Law, which describes the solubility of gases in liquids under pressure.

Question 21: What is the van’t Hoff factor (i) for a solute that undergoes dimerization in solution (e.g., acetic acid in benzene)? (A) 1 (B) 2 (C) Between 0 and 1 (D) Greater than 1

Explanation 21:

Correct Answer: (C)
Reasoning: When dimerization occurs, two molecules associate to form one particle (n=2 in association formula). The number of particles in solution decreases. i=1+(1/n−1)α=1+(1/2−1)α=1−α/2. Since α (degree of association) is between 0 and 1, ‘i’ will be between 0.5 and 1 (i.e., less than 1).

Question 22: An azeotropic mixture of two liquids: (A) Boils at different temperatures. (B) Can be separated by fractional distillation. (C) Has the same composition in liquid and vapor phases. (D) Shows positive deviation from Raoult’s Law only.

Explanation 22:

Correct Answer: (C)
Reasoning: Azeotropes are constant boiling mixtures that have the same composition in both the liquid and vapor phases, meaning they cannot be separated by fractional distillation. They can show either positive or negative deviation from Raoult’s Law.

Question 23: If 5.85 g of NaCl (Molar mass 58.5 g/mol) is dissolved in 100 mL of water, what is the approximate molarity of the solution? (Assume volume of solution is 100 mL) (A) 0.1 M (B) 1.0 M (C) 0.5 M (D) 2.0 M

Explanation 23:

Correct Answer: (B)
Reasoning: Moles of NaCl=5.85 g/58.5 g/mol=0.1 mol. Volume of solution = 100 mL=0.1 L. Molarity = Moles of solute / Volume of solution (L) = 0.1 mol/0.1 L=1.0 M.

Question 24: Which of the following pairs will form an ideal solution? (A) Ethanol and acetone (B) Chloroform and acetone (C) n-hexane and n-heptane (D) Nitric acid and water

Explanation 24:

Correct Answer: (C)
Reasoning: Ideal solutions are formed by liquids with very similar structures and intermolecular forces. n-hexane and n-heptane are both non-polar alkanes with similar van der Waals forces. The other pairs show significant deviations from ideality due to differences in intermolecular interactions.

Question 25: How does the solubility of a gas in a liquid change with increasing temperature? (A) Increases (B) Decreases (C) Remains constant (D) First increases then decreases

Explanation 25:

Correct Answer: (B)
Reasoning: The dissolution of gases in liquids is an exothermic process. According to Le Chatelier’s principle, increasing temperature favors the reverse (endothermic) process, i.e., evolution of gas, leading to a decrease in solubility.

Question 26: The unit of molarity is: (A) mol kg−1 (B) mol L−1 (C) g L−1 (D) mol

Explanation 26:

Correct Answer: (B)
Reasoning: Molarity is defined as moles of solute per litre of solution, so its units are mol L−1.

Question 27: A solution of sucrose (a non-electrolyte) has a freezing point of −0.186∘C. What is its molality? (Kf for water=1.86 K kg mol−1) (A) 0.05 m (B) 0.1 m (C) 0.2 m (D) 0.01 m

Explanation 27:

Correct Answer: (B)
Reasoning: ΔTf=Tf0−Tf=0∘C−(−0.186∘C)=0.186 K. ΔTf=Kf×m m=ΔTf/Kf=0.186 K/1.86 K kg mol−1=0.1 mol kg−1=0.1 m.

Question 28: Which of the following concentration terms is defined as “moles of solute per kg of solvent”? (A) Molarity (B) Normality (C) Mole fraction (D) Molality

Explanation 28:

Correct Answer: (D)
Reasoning: This is the definition of molality.

Question 29: A gas has a higher KH value at a given temperature. This implies: (A) Higher solubility of the gas. (B) Lower solubility of the gas. (C) Solubility is independent of pressure. (D) The gas is highly reactive.

Explanation 29:

Correct Answer: (B)
Reasoning: From Henry’s Law (p=KH×χ), for a given partial pressure ‘p’, a higher KH means a smaller mole fraction (χ) of the gas in the solution, implying lower solubility.

Question 30: An isotonic solution with blood plasma (0.9% NaCl solution) would cause red blood cells to: (A) Swell (B) Shrink (C) Remain unchanged (D) Burst

Explanation 30:

Correct Answer: (C)
Reasoning: Isotonic solutions have the same osmotic pressure. When placed in an isotonic solution, red blood cells neither gain nor lose water by osmosis and thus remain unchanged.

Question 31: What is the sum of mole fractions of all components in a solution? (A) Always 0 (B) Always 1 (C) Can be greater than 1 (D) Depends on the number of components

Explanation 31:

Correct Answer: (B)
Reasoning: By definition, the sum of mole fractions of all components in any mixture (including a solution) is always equal to 1.

Question 32: Why are gases less soluble in water at higher temperatures? (A) Dissolution of gases is an exothermic process. (B) Dissolution of gases is an endothermic process. (C) Water molecules become more tightly packed. (D) Gases become less reactive at higher temperatures.

Explanation 32:

Correct Answer: (A)
Reasoning: The dissolution of gases in liquids is an exothermic process (ΔH<0). According to Le Chatelier’s principle, increasing temperature favors the reverse (endothermic) process, which is the escape of gas from the solution, leading to decreased solubility.

Question 33: An aqueous solution of a substance has an observed molar mass which is less than its normal molar mass. This indicates that the substance is undergoing: (A) Association (B) Dissociation (C) No change (D) Polymerization

Explanation 33:

Correct Answer: (B)
Reasoning: If a substance dissociates into more particles, the observed colligative property will be higher, and the observed molar mass (calculated using colligative properties) will be lower than the normal molar mass. This is reflected by a van’t Hoff factor (i) > 1.

Question 34: Which of the following is a minimum boiling azeotrope? (A) Nitric acid-water mixture (B) Chloroform-acetone mixture (C) Ethanol-water mixture (D) Benzene-toluene mixture

Explanation 34:

Correct Answer: (C)
Reasoning: Ethanol-water mixture (containing about 95.6% ethanol) shows a large positive deviation from Raoult’s Law and forms a minimum boiling azeotrope. Nitric acid-water forms a maximum boiling azeotrope. Chloroform-acetone shows negative deviation. Benzene-toluene forms an ideal solution.

Question 35: The vapour pressure of a solution containing a non-volatile solute is directly proportional to the: (A) Mole fraction of solute (B) Mole fraction of solvent (C) Molality of solution (D) Molarity of solution

Explanation 35:

Correct Answer: (B)
Reasoning: According to Raoult’s Law for non-volatile solutes, the vapor pressure of the solution is directly proportional to the mole fraction of the solvent. (pA=pA0×χA).

Question 36: An increase in pressure over the solution of a gas in a liquid: (A) Decreases the solubility of the gas. (B) Increases the solubility of the gas. (C) Has no effect on the solubility of the gas. (D) Increases the temperature of the solution.

Explanation 36:

Correct Answer: (B)
Reasoning: According to Henry’s Law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Thus, increasing pressure increases solubility.

Question 37: What is the physical state of the solvent in an amalgam? (A) Gas (B) Liquid (C) Solid (D) Plasma

Explanation 37:

Correct Answer: (B)
Reasoning: An amalgam is a solution where mercury (a liquid) is the solvent, and a metal (solid) like sodium or silver is the solute.

Question 38: Why is molality preferred over molarity for expressing concentration in colligative property calculations? (A) Molality is easier to calculate. (B) Molality is independent of temperature. (C) Molarity is too small. (D) Molality is always a larger value.

Explanation 38:

Correct Answer: (B)
Reasoning: Colligative properties are often studied at varying temperatures. Since molality is based on mass of solvent, it remains constant with temperature, unlike molarity which changes with volume (and thus temperature). This makes molality a more reliable concentration unit for colligative properties.

Question 39: Which of the following is a direct application of Henry’s Law? (A) Salt dissolving in water. (B) Soda water bottles sealed under high pressure. (C) Boiling of water. (D) Freezing of water in winter.

Explanation 39:

Correct Answer: (B)
Reasoning: Soda water (carbonated beverages) bottles are sealed under high carbon dioxide pressure to increase the solubility of CO2 in the drink, which is a direct application of Henry’s Law.

Question 40: If 0.1 M solution of NaCl and 0.1 M solution of Urea are at the same temperature, which one will have higher osmotic pressure? (A) NaCl solution (B) Urea solution (C) Both will have the same osmotic pressure. (D) Cannot be determined.

Explanation 40:

Correct Answer: (A)
Reasoning: Osmotic pressure is a colligative property and depends on the number of particles. NaCl dissociates into 2 ions (Na+ and Cl−), so its van’t Hoff factor (i) is 2. Urea is a non-electrolyte, so its i-value is 1. Since the molar concentration is the same, the NaCl solution will have twice the effective number of particles, thus exhibiting higher osmotic pressure (π=iCRT).