An aqueous solution contains 3.00% phenylalanine (C 9 H 11 NO 2 ) by mass. (Phenylalanine is non-ionic and nonvolatile.) Find the following: (a) the freezing point of the solution (b) the boiling point of the solution (c) the osmotic pressure of the solution at 25 °C In your view, which of these values is most easily measurable in the laboratory?

Interpretation: The freezing point of the given solution has to be determined.

Concept introduction:

Colligative properties: Properties of solutions which having influence on the concentration of the solute in it. Colligative properties are,

• Decrease in the vapor pressure
• Increase in the boiling point
• Decline in the freezing point
• Osmotic pressure

Change in freezing point is calculated by using the equation,

  ΔTfp = Kfp msolute

  where,

  Kfp  is the molal freezing point elevation constant.

Molality (m): Molality is the number of moles of solute present in one kilogram of solvent.

  Molality (m) =Number of moles of solute1kg of solvent

Given,

Mass of phenylalanine is 3% = 3100 × 100 g = 3 g

Mass of solvent is 100 g − 3 g = 97 g = 0.097 kg

Molar mass of phenylalanine is 165.19 g/mol

Molal freezing point elevation constant of water is  −1.860C m−1

  Number of mole =Given mass of the substanceMolar mass = 3 g phenylalanine165.19 g/mol = 0

Interpretation: The boiling point of the given solution has to be determined.

Concept introduction:

Colligative properties: Properties of solutions which having influence on the concentration of the solute in it. Colligative properties are,

• Decrease in the vapor pressure
• Increase in the boiling point
• Decline in the freezing point
• Osmotic pressure

Change in boiling point is calculated by using the equation,

  ΔTbp = Kbp msolute

  where,

  Kbp  is the molal boiling point elevation constant.

Molality (m): Molality is the number of moles of solute present in one kilogram of solvent.

  Molality (m) =Number of moles of solute1kg of solvent

Interpretation: The osmotic pressure of the given solution has to be determined. The values that are easily measureable in laboratory have to be identified among these values.

Concept introduction:

Colligative properties: Properties of solutions which having influence on the concentration of the solute in it. Colligative properties are,

• Decrease in the vapor pressure
• Increase in the boiling point
• Decline in the freezing point
• Osmotic pressure

Osmotic pressure is calculated by using the equation,

  π = cRT

  where,

  c is the molar concentration.

Molality (m): Molality is the number of moles of solute present in one kilogram of solvent.

  Molality (m) =Number of moles of solute1kg of solvent