Worksheet: Cryoscopy and Ebullioscopy

In this worksheet, we will practice calculating the molar mass of a solute based on its effect on the melting or boiling point of the solvent.

Q1:

When 6.29 g of a nonvolatile solute is dissolved in 500 g of water, the freezing point of the resultant aqueous solution is 0.646C lower than that of pure water. The cryoscopic constant for water is 𝐾=1.856/Kkgmol and the solute does not dissociate. Estimate the molar mass of the solute.

Q2:

A sample of sulfur weighing 0.201 g was dissolved in 17.8 g of carbon disulfide, CS2(𝐾=2.43/)bCm. If the boiling point of the carbon disulfide was elevated by 0.107C, what is the formula of a sulfur molecule in this solution?

  • A S
  • B S 4
  • C S 2
  • D S 8
  • E S 5

Q3:

Lysozyme is an enzyme that cleaves cell walls. A 0.100 L sample of a solution of lysozyme containing 0.0750 g of the enzyme exhibits an osmotic pressure of 1.32×10 atm at 25C. What is the molar mass of lysozyme?

  • A 3 . 4 5 × 1 0 g/mol
  • B 6 . 0 8 × 1 0 g/mol
  • C 4 . 5 0 × 1 0 g/mol
  • D 1 . 3 9 × 1 0 g/mol
  • E 1 . 3 2 × 1 0 g/mol

Q4:

Why are soaps useful for cleaning?

  • AThis causes the materials to swell and become less sticky, allowing them to be removed by water.
  • BSoaps are amphiphilic molecules that help emulsify hydrophobic substances, allowing them to be removed by water.
  • CSoaps lower the viscosity of water. This allows it to penetrate hydrophobic substances more easily, breaking them into smaller particles that can be mechanically removed.
  • DSoaps are very reactive and decompose grease into smaller particles that can be dissolved by water.
  • ESoap molecules function as “molecular sandpaper”: the hydrophobic tails of the molecules are inserted between molecules of an insoluble substance, mechanically separating them into smaller particles that can be dissolved by water.

Q5:

A sample of an organic compound (a nonelectrolyte) weighing 1.30 g lowered the freezing point of 10.0 g of benzene (𝐾=5.12/)fCm by 3.66C. What is the molar mass of the compound?

Q6:

A 12.0 g sample of a nonelectrolyte is dissolved in 80.0 g of water. The solution freezes at 1.94C. What is the molar mass of this solute? The freezing point depression constant of water is 1.86/Cm.

Q7:

When 5.00 g of a nonionic compound is dissolved in 25.00 g of carbon tetrachloride (boiling point 76.8C, 𝐾=5.02/)bKkgmol, the boiling point of the solution at 1 atm is 81.5C. Calculate the molar mass of the nonionic compound.

Q8:

A 2.43 mol/kg aqueous solution of glycerin (CHO)383 was prepared by mixing glycerin with 0.500 kg of water.

What mass of glycerin was required?

What is the freezing point of this solution? The freezing point depression constant of water is 1.86 kg⋅K/mol.

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