Determine the boiling point of a solution that contains 78.8 g of naphthalene (C₁₀H₈, molar mass = 128.16 g/mol)dissolved in 722 mL of benzene (d = 0.877 g/mL).Pure benzene has a boiling point of 80.1°C and a boiling point elevation constant of 2.53°C/m. A) 2.2°C B) 2.5°C C) 82.3°C D) 80.4°C E) 82.6°C

Question

Quizplus · Accepted Answer

First, calculate the moles of naphthalene:

78.8 g / 128.16 g/mol = 0.614 mol

Next, calculate the molality of the solution:

molality = moles of solute / mass of solvent in kg

mass of solvent = density x volume = 0.877 g/mL x 722 mL = 640 g

molality = 0.614 mol / 0.64 kg = 0.959 mol/kg

Now, calculate the boiling point elevation:

ΔTb = Kb x molality

Kb for benzene is 2.53 °C/m

ΔTb = 2.53 °C/m x 0.959 mol/kg = 2.43 °C

Finally, the boiling point of the solution is:

Boiling point = pure boiling point + ΔTb

Boiling point = 80.1 °C + 2.43 °C = 82.53 °C

Rounding to the nearest tenth gives the final answer of 82.6 °C (choice E).

Determine the Boiling Point of a Solution That Contains 78