An aqueous solution contains 3.00 % phenylalanine (C9H11NO2) (MM = 165.21g/mole)

Question

Explanation / Answer

The freezing point of the solution Tf = - 0.35 °C

The boiling point of the solution Tb = 100.10 °C

Explanation:

Given, 3.00 % phenylalanine (C9H11NO2)

Let us assume to have 100g of solution

Then, mass of solute = 100g solution x (3g solute / 100g solution) = 3g
hence, mass solvent = 100g solution - 3g solute = 97g solvent = 0.097kg
and volume of solution = 100g solution x (1mL / 1.00g) = 100 mL solution = 0.100L

Now, we known molality is moles of solute per Kg of solvent.
i.e., molality = (3g/165.21g)/0.097kg = 0.187 m

We also known Tf solution = Kf x m x i = 1.86°C/m x 0.187m x 1 = 0.35°C

Tf = 0 - Tf = - 0.35°C

Tb = Kb x m x i = 0.512°C/m x 0.187m x 1 = 0.10°C

Tb solution = 100 + Tb = 100.10°C

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