Colligative Properties

01

PYQ 2023

medium

chemistry ID: up-board

Find the osmotic pressure of urea solution at 27 C. (R = 0.0821 litre atm K mol)

02

PYQ 2023

medium

chemistry ID: up-board

Calculate the mass of a non-volatile solute (molar mass) which should be dissolved in octane to reduce its vapour pressure to 80%.}

Official Solution

Correct Option: (1)

$Step 1: Apply Raoult’s Law. Given: Thus, Step 2: Relation between mole fractions. Step 3: Calculate moles of solvent. Molar mass of octane = Mass of octane = Step 4: Substitute values. Step 5: Calculate mass of solute. Molar mass = Conclusion: The required mass of solute is:$

03

PYQ 2023

medium

chemistry ID: up-board

$Differentiate between molar and molal elevation constants. Give two different formulae involving these two constants for the determination of molecular mass of solute.$

Official Solution

Correct Option: (1)

$Step 1: Definitions. \begin{itemize} \item Molar elevation constant (K ): It is the elevation of boiling point produced when one mole of solute is dissolved in 1 litre of solvent. \item Molal elevation constant (K ): It is the elevation of boiling point produced when one mole of solute is dissolved in 1000 g (1 kg) of solvent. \end{itemize} Step 2: Formula with molal elevation constant. where, Thus, Here, = mass of solute, = mass of solvent in g, = molar mass of solute. Step 3: Formula with molar elevation constant. where, (molar concentration) Thus, Here, = volume of solvent in litres. Conclusion: Molar elevation constant is defined with respect to litre of solvent, while molal elevation constant is defined with respect to kg of solvent. Both can be used to calculate molar mass of solute.$

04

PYQ 2024

medium

chemistry ID: up-board

$Write general electronic configuration of d-block and f-block elements.$

Official Solution

Correct Option: (1)

$- d-block elements: . - f-block elements: .$

05

PYQ 2024

medium

chemistry ID: up-board

$Which is not a colligative property of solution?$

1

$Osmotic pressure$

2

$Depression in freezing point$

3

$Surface tension$

4

$Lowering in vapour pressure$

Official Solution

Correct Option: (3)

$Step 1: Understanding Colligative Properties Colligative properties depend only on the number of solute particles in a solution, not their identity. The four main colligative properties are Relative lowering of vapor pressure Boiling point elevation Freezing point depression Osmotic pressure Since surface tension is not influenced by the number of solute particles but by intermolecular forces, it is not a colligative property.$

06

PYQ 2024

easy

chemistry ID: up-board

$State Raoult's law related to lowering of vapour pressure. Calculate the vapour pressure of pure water at 293 K temperature when 25 g of glucose is dissolved in 450 g of water. Vapour pressure of pure water at 293 K temperature is 1535 mmHg.$

Official Solution

Correct Option: (1)

07

PYQ 2024

easy

chemistry ID: up-board

$What is the effect of catalyst on the rate of reaction? A first-order reaction is 40\% completed in 50 minutes. Calculate the time taken for 80\% completion of the reaction. (Given: and )$

Official Solution

Correct Option: (1)

08

PYQ 2024

easy

chemistry ID: up-board

$Define molal depression constant. Calculate the freezing point of the aqueous solution containing 25 g of ethylene glycol (C H O) in 300 g of water. The value of molal depression constant for water is 1.86 K kg mol and freezing point of water is 273.15 K.$

Official Solution

Correct Option: (1)

09

PYQ 2024

medium

chemistry ID: up-board

$2.82 g of glucose (molar mass = 180 g mol) is dissolved in 30 g of water. Calculate the molality of the solution.$

Official Solution

Correct Option: (1)

$Step 1: Formula for Molality: Step 2: Calculate Moles of Glucose: Step 3: Convert Solvent Mass to kg: Step 4: Calculate Molality: Thus, the molality of the solution is 0.522 mol/kg.$

10

PYQ 2024

medium

chemistry ID: up-board

$What is osmotic pressure? Explain the difference between osmosis and diffusion with an example.$

Official Solution

Correct Option: (1)

$Step 1: Definition: Osmotic pressure is the pressure required to stop the osmotic flow of solvent molecules across a semipermeable membrane. Step 2: Difference Between Osmosis and Diffusion: \begin{center} \begin{tabular}{|c|c|} \hline Osmosis & Diffusion \hline Movement of solvent & Movement of solute \hline Requires a membrane & No membrane needed \hline Example: Water absorption by roots & Example: Perfume spreading in air \hline \end{tabular} \end{center}$

11

PYQ 2024

medium

chemistry ID: up-board

$The colligative property is$

1

$Osmotic pressure$

2

$Surface tension$

3

$Density$

4

$All of these$

Official Solution

Correct Option: (1)

$Step 1: Definition of Colligative Properties:} Colligative properties depend on the number of solute particles in a solution and include: - Osmotic Pressure - Boiling Point Elevation - Freezing Point Depression - Vapor Pressure Lowering Step 2: Why not other options: - Surface tension and density depend on the nature of the substance, not the number of solute particles.$

12

PYQ 2024

medium

chemistry ID: up-board

$Explain the reason for depression in vapour pressure. At any temperature, the vapour pressure of pure solvent is 0.745 bar. non-volatile solute was dissolved in solvent (molar mass). The vapour pressure of the solution so obtained is 0.740 bar. Find out the molar mass of the solid.$

Official Solution

Correct Option: (1)

$Depression in Vapour Pressure: Relative lowering of vapour pressure: Given: Substitute values: Simplify:$

13

PYQ 2024

medium

chemistry ID: up-board

$Explain Raoult's law for solutions containing non-volatile solute in volatile solvent. Derive mathematical expression for this law.$

Official Solution

Correct Option: (1)

$Step 1: Statement of Raoultâ€™s Law: Raoultâ€™s law states that the partial vapor pressure of a solvent in a solution is directly proportional to its mole fraction. where is the partial vapor pressure of the solvent, is its mole fraction, and is the vapor pressure of the pure solvent. Step 2: Mathematical Derivation: For a solution containing a non-volatile solute: Substituting in Raoultâ€™s law: Step 3: Relative Lowering of Vapor Pressure:} Thus, the relative lowering of vapor pressure is equal to the mole fraction of the solute.$

14

PYQ 2024

medium

chemistry ID: up-board

$The colligative property of a solution depends upon$

1

$the number of particles of solute$

2

$the nature of particles of solute$

3

$the nature of particles of solvent$

4

$the nature of particles of both solute and solvent$

Official Solution

Correct Option: (1)

$Step 1: Colligative properties (such as boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering) depend only on the number of solute particles, not their identity. Step 2: These properties are a function of solute concentration, not the chemical nature of solute or solvent.$

15

PYQ 2024

medium

chemistry ID: up-board

$Define molal elevation constant. Calculate the boiling point of an aqueous solution containing 0.6 g of urea (molar mass = 60) in 100 g of water. The value of molal elevation constant for water is 0.52 K kg mol and boiling point of water is 373.15 K.$

Official Solution

Correct Option: (1)

$Step 1: Definition: The molal elevation constant () is the increase in boiling point when 1 mole of a non-volatile solute is dissolved in 1 kg of solvent. Step 2: Formula for Boiling Point Elevation:} where, Step 3: Calculate Molality: Step 4: Calculate Boiling Point Elevation: Step 5: Final Boiling Point: Thus, the boiling point of the solution is 373.20 K.$

16

PYQ 2025

easy

chemistry ID: up-board

$Explain Raoult's Law. The vapour pressure of chloroform () and dichloromethane () are 200 mm Hg and 4.5 mm Hg respectively at 298 K. Calculate the vapour pressure of the solution formed by mixing 51 g of and 20 g of at 298 K.$

Official Solution

Correct Option: (1)

$Raoult's Law states that the partial vapor pressure of each volatile component in a solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution. Mathematically, it is represented as: Where: - is the partial vapor pressure of component , - is the mole fraction of component in the solution, - is the vapor pressure of the pure component . Given: - Vapor pressure of chloroform , - Vapor pressure of dichloromethane , - Mass of chloroform , - Mass of dichloromethane , - Molar mass of chloroform , - Molar mass of dichloromethane . Step 1: Calculate moles of each component. For chloroform: For dichloromethane: Step 2: Calculate total moles in the solution. Total moles = . Step 3: Calculate mole fractions. Mole fraction of chloroform: Mole fraction of dichloromethane: Step 4: Apply Raoult's Law to calculate the total vapor pressure. Vapor pressure of the solution is the sum of the partial pressures: Thus, the vapor pressure of the solution is .$

17

PYQ 2025

medium

chemistry ID: up-board

$Find the osmotic pressure of urea solution at \ (Given: L\,atm\,K \,mol ).}$

Official Solution

Correct Option: (1)

$For a non-electrolyte (urea), osmotic pressure is given by with . Given, .$

18

PYQ 2025

medium

chemistry ID: up-board

$Define Raoult's Law and explain it.$

Official Solution

Correct Option: (1)

$Definition: Raoult's Law states that the relative lowering of vapour pressure of a solution is equal to the mole fraction of the solute. For a solution containing a non-volatile solute: where: - = vapour pressure of solvent in solution, - = vapour pressure of pure solvent, - = mole fraction of solvent. Explanation: Adding a non-volatile solute decreases the mole fraction of solvent. As vapour pressure is directly proportional to solvent mole fraction, the vapour pressure decreases. The relative lowering of vapour pressure is: where is the mole fraction of solute. Thus, Raoult's Law explains colligative properties like relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.$

19

PYQ 2025

easy

chemistry ID: up-board

$The aqueous solution having maximum boiling point is$

1

$1% Glucose$

2

$1% NaCl$

3

$1% CaCl$

4

$1% Sucrose$

Official Solution

Correct Option: (3)

$Step 1: Recall the concept. Boiling point elevation is a colligative property, which depends on the number of solute particles in solution (van’t Hoff factor). Step 2: Compare solutes. - Glucose and sucrose are non-electrolytes: . - NaCl dissociates into 2 ions: . - CaCl dissociates into 3 ions: . Step 3: Apply formula. . The greater the, the higher the elevation in boiling point. Step 4: Conclude. CaCl produces maximum number of particles, hence maximum boiling point elevation. Final Answer: % Quciktip$

20

PYQ 2025

medium

chemistry ID: up-board

$What is the relation between depression in freezing point and molar mass of the solute?$

Official Solution

Correct Option: (1)

$The depression in freezing point () is directly proportional to the molality of the solution. The relation is: where is the molal depression constant of the solvent and is molality. Since molality, where: - = mass of solute (g), - = molar mass of solute (g mol), - = mass of solvent (g). Thus, molar mass of solute can be calculated as:$

21

PYQ 2025

medium

chemistry ID: up-board

$The vapour pressure of pure benzene at any temperature is 0.850 bar. 0.5 g non-volatile non-electrolytic solid is dissolved in 39.0 g benzene (molar mass 78 g mol). The vapour pressure of the solution is 0.845 bar. Calculate the molar mass of the solid.$

Official Solution

Correct Option: (1)

$For a non–volatile solute, Raoult's law gives relative lowering of vapour pressure: Given: bar,\; bar bar. Mass of benzene g, g mol mol. Mass of solute g, molar mass mol. Step 1: Compute relative lowering. Step 2: Apply Raoult's relation. Multiply numerator and denominator by :$

22

PYQ 2025

medium

chemistry ID: up-board

$What is elevation of boiling point? A liquid has boiling point 353.23 K. The boiling point of solution becomes 354.11 K after dissolving 1.8 g non-volatile solute of molar mass 58 g mol to 90 g liquid. Calculate boiling point elevation constant for the liquid.}$

Official Solution

Correct Option: (1)

$The elevation in boiling point is given by the formula: Where: - = elevation in boiling point - = molal elevation constant - = molality of the solution Step 1: Calculate elevation in boiling point. Step 2: Calculate number of moles of solute. Mass of solute Molar mass of solute Step 3: Calculate mass of solvent in kilograms. Mass of solvent Step 4: Calculate molality of solution. Step 5: Calculate boiling point elevation constant. Thus, the boiling point elevation constant for the liquid is .$

23

PYQ 2025

medium

chemistry ID: up-board

$Explain Raoult's Law.$

Official Solution

Correct Option: (1)

$Raoult's Law states that the partial vapor pressure of a component in a liquid solution is directly proportional to its mole fraction in the solution. Where: - = partial vapor pressure of component A in solution, - = mole fraction of component A in solution, - = vapor pressure of pure component A. For a binary solution (components A and B), the total vapor pressure is: Significance: - Raoult's Law helps in understanding colligative properties like relative lowering of vapor pressure, elevation of boiling point, depression of freezing point, and osmotic pressure. - It is valid for ideal solutions where intermolecular interactions between unlike molecules are similar to those between like molecules.$

24

PYQ 2025

medium

chemistry ID: up-board

$6 g urea is dissolved in 200 g water. Calculate the elevation in boiling point. Molal elevation constant for water is 0.52 K kg mol .}$

Official Solution

Correct Option: (1)

$Elevation of boiling point is given by . Here and is molality. Step 1: Moles of urea (solute). Molar mass of urea . . Step 2: Mass of solvent (water) in kg. . Step 3: Molality. . Step 4: Elevation in boiling point. .$

25

PYQ 2025

medium

chemistry ID: up-board

$Write the definition of osmotic pressure. Calculate the osmotic pressure of 2% aqueous solution of urea at 27 C. Solution constant .}$

Official Solution

Correct Option: (1)

$Definition: Osmotic pressure is the excess pressure that must be applied to a solution separated from its pure solvent by a semipermeable membrane to prevent the net flow of solvent into the solution. Formula (for a non-electrolyte): Given/Assumption: 2% (w/v) solution . Molar mass of urea . Temperature . Step 1: Molarity . Mass per litre . Step 2: Osmotic pressure.$

26

PYQ 2025

medium

chemistry ID: up-board

$What is the relation between elevation in boiling point and molality?$

Official Solution

Correct Option: (1)

$The elevation in boiling point () is directly proportional to the molality () of the solution. Where: -, elevation in boiling point, - = molal elevation constant (ebullioscopic constant) of the solvent, - = molality of the solution (mol solute per kg solvent). Thus, higher the molality of the solution, greater is the elevation in boiling point.$

27

PYQ 2025

medium

chemistry ID: up-board

$At what temperature does a 5% (w/v) solution of glucose produce 7 atmospheric osmotic pressure?$

Official Solution

Correct Option: (1)

$Step 1: Use the osmotic pressure formula. The formula for osmotic pressure is: Where: = Osmotic pressure = 7 atm = Moles of solute = Ideal gas constant = 0.0821 L atm / K mol = Temperature in Kelvin = Volume of the solution = 1 L (assumed for simplicity) Step 2: Moles of glucose (n). Given that the solution is 5% (w/v), this means 5 g of glucose is present in 100 ml of solution. So, for 1 liter (1000 ml), there will be: Molar mass of glucose is: Moles of glucose = Step 3: Calculate temperature (T). Substitute the known values into the osmotic pressure equation: Solving for : Final Answer:$

28

PYQ 2025

medium

chemistry ID: up-board

$Which one between 0.1 M Urea and 0.1 M NaCl solution will have greater osmotic pressure? Explain the reason.$

Official Solution

Correct Option: (1)

$Step 1: Osmotic Pressure Formula The osmotic pressure () is given by the formula: where, - = van’t Hoff factor (number of particles into which a solute dissociates), - = molarity of the solution, - = universal gas constant, - = temperature in Kelvin. Step 2: Analyze Urea and NaCl - Urea does not dissociate in water, so . - NaCl dissociates into two ions: Na and Cl, so . Step 3: Compare Osmotic Pressure Given that NaCl dissociates into more particles, the osmotic pressure for NaCl will be higher than that for Urea, even though both have the same molarity. Final Answer: The 0.1 M NaCl solution will have greater osmotic pressure. Correct Answer: (NaCl has higher osmotic pressure)$

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Colligative Properties

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Chapter Questions 28 MCQs

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Chapter Questions
28 MCQs