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Colligative Properties: Freezing Point Depression & Boiling Point Elevation – Step-by-Step Guidance

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Q1. Calculate the molality, freezing point, and boiling point for a solution made by dissolving 144 g of C6H12O6 in 1000 g of H2O.

Background

Topic: Colligative Properties – Freezing Point Depression & Boiling Point Elevation

This question tests your understanding of how to calculate molality and use it to determine the freezing and boiling points of a solution, applying the concepts of colligative properties.

Key Terms and Formulas

  • Molality ():

  • Freezing Point Depression:

  • Boiling Point Elevation:

  • For water: ,

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the number of moles of glucose () using its molar mass. The molar mass is calculated by adding the atomic masses: (C) (H) (O).

  2. Find the molality () of the solution using the formula . Here, the mass of water is 1000 g (which is 1.000 kg).

  3. Calculate the freezing point depression using . Remember, for glucose.

  4. Determine the new freezing point by subtracting from the normal freezing point of water ().

  5. Calculate the boiling point elevation using and add this value to the normal boiling point of water () to find the new boiling point.

Try solving on your own before revealing the answer!

Q2. Calculate the molality, freezing point, and boiling point for a solution made by dissolving 48 g of CH3OH in 200 g of H2O.

Background

Topic: Colligative Properties – Freezing Point Depression & Boiling Point Elevation

This question asks you to apply the same concepts as above, but with different masses and a different solute (methanol).

Key Terms and Formulas

  • Molality ():

  • Freezing Point Depression:

  • Boiling Point Elevation:

  • For water: ,

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the molar mass of methanol (): (C) (H) (O).

  2. Find the number of moles of methanol using the given mass (48 g).

  3. Calculate the molality () using the mass of water (200 g = 0.200 kg).

  4. Use to find the freezing point depression, and for boiling point elevation.

  5. Adjust the normal freezing and boiling points of water accordingly to find the new values.

Try solving on your own before revealing the answer!

Q3. Calculate the molality, freezing point, and boiling point for a solution made by dissolving 184 g of C2H5OH in 400 g of H2O.

Background

Topic: Colligative Properties – Freezing Point Depression & Boiling Point Elevation

This question is similar to the previous ones, but with ethanol as the solute and a different solvent mass.

Key Terms and Formulas

  • Molality ():

  • Freezing Point Depression:

  • Boiling Point Elevation:

  • For water: ,

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the molar mass of ethanol (): (C) (H) (O).

  2. Determine the number of moles of ethanol using the given mass (184 g).

  3. Calculate the molality () using the mass of water (400 g = 0.400 kg).

  4. Apply and to find the changes in freezing and boiling points.

  5. Adjust the normal freezing and boiling points of water to find the new values.

Try solving on your own before revealing the answer!

Q4. Calculate the molality, freezing point, and boiling point for a solution made by dissolving 600 g of C3H7OH in 600 g of H2O.

Background

Topic: Colligative Properties – Freezing Point Depression & Boiling Point Elevation

This question involves calculating colligative properties for a solution with propanol as the solute.

Key Terms and Formulas

  • Molality ():

  • Freezing Point Depression:

  • Boiling Point Elevation:

  • For water: ,

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the molar mass of propanol (): (C) (H) (O).

  2. Find the number of moles of propanol using the given mass (600 g).

  3. Calculate the molality () using the mass of water (600 g = 0.600 kg).

  4. Use and to find the changes in freezing and boiling points.

  5. Adjust the normal freezing and boiling points of water to find the new values.

Try solving on your own before revealing the answer!

Q5. Calculate the molality, freezing point, and boiling point for a solution made by dissolving 100 g of C2H6O2 in 200 g of H2O.

Background

Topic: Colligative Properties – Freezing Point Depression & Boiling Point Elevation

This question involves ethylene glycol as the solute and requires the same approach as previous questions.

Key Terms and Formulas

  • Molality ():

  • Freezing Point Depression:

  • Boiling Point Elevation:

  • For water: ,

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the molar mass of ethylene glycol (): (C) (H) (O).

  2. Find the number of moles of ethylene glycol using the given mass (100 g).

  3. Calculate the molality () using the mass of water (200 g = 0.200 kg).

  4. Use and to find the changes in freezing and boiling points.

  5. Adjust the normal freezing and boiling points of water to find the new values.

Try solving on your own before revealing the answer!

Q6. Calculate the molality of a water solution if the freezing point is -9.3°C.

Background

Topic: Colligative Properties – Freezing Point Depression

This question tests your ability to work backwards from a measured freezing point to determine the molality of the solution.

Key Terms and Formulas

  • Freezing Point Depression:

  • For water:

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the change in freezing point: .

  2. Set up the equation and solve for (molality).

  3. Plug in the values: , , .

  4. Rearrange to solve for : .

Try solving on your own before revealing the answer!

Q7. Calculate the molality of a water solution if the freezing point is -27.9°C.

Background

Topic: Colligative Properties – Freezing Point Depression

This question is similar to Q6, but with a larger freezing point depression.

Key Terms and Formulas

  • Freezing Point Depression:

  • For water:

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the change in freezing point: .

  2. Set up the equation and solve for .

  3. Plug in the values: , , .

  4. Rearrange to solve for : .

Try solving on your own before revealing the answer!

Q8. Calculate the molality of a water solution if the freezing point is -7.44°C.

Background

Topic: Colligative Properties – Freezing Point Depression

This question is similar to Q6 and Q7, but with a different freezing point.

Key Terms and Formulas

  • Freezing Point Depression:

  • For water:

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the change in freezing point: .

  2. Set up the equation and solve for .

  3. Plug in the values: , , .

  4. Rearrange to solve for : .

Try solving on your own before revealing the answer!

Q9. Calculate the molality of a water solution if the boiling point is 103.12°C.

Background

Topic: Colligative Properties – Boiling Point Elevation

This question asks you to determine the molality of a solution from its elevated boiling point.

Key Terms and Formulas

  • Boiling Point Elevation:

  • For water:

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the change in boiling point: .

  2. Set up the equation and solve for .

  3. Plug in the values: , , .

  4. Rearrange to solve for : .

Try solving on your own before revealing the answer!

Q10. Calculate the molality of a water solution if the boiling point is 108.32°C.

Background

Topic: Colligative Properties – Boiling Point Elevation

This question is similar to Q9, but with a larger boiling point elevation.

Key Terms and Formulas

  • Boiling Point Elevation:

  • For water:

  • Van't Hoff factor (): For nonionizing solutes,

Step-by-Step Guidance

  1. Calculate the change in boiling point: .

  2. Set up the equation and solve for .

  3. Plug in the values: , , .

  4. Rearrange to solve for : .

Try solving on your own before revealing the answer!

Q11. What is the boiling point of a solution made by dissolving 31 g of NaCl in 559 g of water? (Assume 100% ionization of NaCl.)

Background

Topic: Colligative Properties – Boiling Point Elevation (Ionic Solute)

This question tests your ability to calculate boiling point elevation for an ionic solute, taking into account the van't Hoff factor () for complete dissociation.

Key Terms and Formulas

  • Boiling Point Elevation:

  • For water:

  • Van't Hoff factor (): For NaCl, (since it dissociates into Na+ and Cl-)

  • Molality ():

Step-by-Step Guidance

  1. Calculate the molar mass of NaCl: (Na) (Cl).

  2. Find the number of moles of NaCl using the given mass (31 g).

  3. Calculate the molality () using the mass of water (559 g = 0.559 kg).

  4. Use for NaCl and plug values into to find the boiling point elevation.

  5. Add to the normal boiling point of water () to find the new boiling point.

Try solving on your own before revealing the answer!

Q12. Calculate the freezing point of a nonionizing antifreeze solution containing 388 g ethylene glycol (C2H6O2) and 409 g of water.

Background

Topic: Colligative Properties – Freezing Point Depression

This question asks you to calculate the freezing point of a solution with a nonionizing solute (ethylene glycol).

Key Terms and Formulas

  • Freezing Point Depression:

  • For water:

  • Van't Hoff factor (): For ethylene glycol,

  • Molality ():

Step-by-Step Guidance

  1. Calculate the molar mass of ethylene glycol (): (C) (H) (O).

  2. Find the number of moles of ethylene glycol using the given mass (388 g).

  3. Calculate the molality () using the mass of water (409 g = 0.409 kg).

  4. Use and plug values into to find the freezing point depression.

  5. Subtract from the normal freezing point of water () to find the new freezing point.

Try solving on your own before revealing the answer!

Q13. Calculate the boiling point of an ionic solution containing 29.7 g Na2SO4 and 84.4 g water. (Assume 100% ionization.)

Background

Topic: Colligative Properties – Boiling Point Elevation (Ionic Solute)

This question involves an ionic solute (sodium sulfate) that dissociates into three ions, so you must use the correct van't Hoff factor.

Key Terms and Formulas

  • Boiling Point Elevation:

  • For water:

  • Van't Hoff factor (): For Na2SO4, (dissociates into 2 Na+ and 1 SO42-)

  • Molality ():

Step-by-Step Guidance

  1. Calculate the molar mass of Na2SO4: (Na) (S) (O).

  2. Find the number of moles of Na2SO4 using the given mass (29.7 g).

  3. Calculate the molality () using the mass of water (84.4 g = 0.0844 kg).

  4. Use and plug values into to find the boiling point elevation.

  5. Add to the normal boiling point of water () to find the new boiling point.

Try solving on your own before revealing the answer!

Q14. What is the molecular mass of a substance if 22.5 g dissolved in 250 g of water produces a solution whose freezing point is -0.930°C?

Background

Topic: Colligative Properties – Determining Molar Mass from Freezing Point Depression

This question tests your ability to use freezing point depression data to determine the molar mass of an unknown solute.

Key Terms and Formulas

  • Freezing Point Depression:

  • For water:

  • Van't Hoff factor (): For nonionizing solutes,

  • Molality ():

  • Moles of solute:

Step-by-Step Guidance

  1. Calculate the change in freezing point: .

  2. Set up the equation and solve for .

  3. Express molality in terms of moles and mass: .

  4. Express moles of solute in terms of molar mass: , where is the molar mass.

  5. Substitute this expression into the molality formula and solve for .

Try solving on your own before revealing the answer!

Q15. If 4.18 g of a nonionic solute is dissolved in 36.30 g of benzene (C6H6), the freezing point is 2.70°C. Find the molar mass of this solute. The freezing point of benzene is 5.53°C and the Kf is 5.12°C/m.

Background

Topic: Colligative Properties – Determining Molar Mass from Freezing Point Depression (Non-aqueous Solvent)

This question asks you to determine the molar mass of a solute using freezing point depression data for benzene, not water.

Key Terms and Formulas

  • Freezing Point Depression:

  • For benzene:

  • Van't Hoff factor (): For nonionizing solutes,

  • Molality ():

  • Moles of solute:

Step-by-Step Guidance

  1. Calculate the change in freezing point: .

  2. Set up the equation and solve for .

  3. Express molality in terms of moles and mass: .

  4. Express moles of solute in terms of molar mass: , where is the molar mass.

  5. Substitute this expression into the molality formula and solve for .

Try solving on your own before revealing the answer!

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